STEAM POWERED ROBOTS

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                                   One of the most significant challenges in the development of an autonomous human-scale robot is the issue of power supply. Perhaps the most likely power supply/actuator candidate system for a position or force actuated human-scale robot is an electrochemical battery and dc motor combination. This type of system, however, would have to carry an inordinate amount of battery weight in order to perform a significant amount of work for a significant period of time.

A state-of-the-art example of a human scale robot that utilizes electrochemical batteries combined with dc motor/harmonic drive actuators is the Honda Motor Corporation humanoid robot model P3. The P3 robot has a total mass of 130 kg (285lb), 30 kg (66 lbs) of which are nickel-zinc batteries. These30 kg of batteries provides sufficient power for approximately 15–25 min of operation, depending on its workload. Operation times of this magnitude are common in self-powered position or force controlled human-scale robots, and represent a major technological roadblock for designing actuated mobile robots that can operate power-autonomously for extended periods of time.

1.1. Figure of Merit

Assuming that a given power supply and actuation system can deliver the requisite average and peak output power at a bandwidth required by a power-autonomous robot, three parameters are of primary interest in providing optimal energetic performance. These are the mass-specific energy density of the power source (Es), the efficiency of converting energy from the power source to controlled mechanical work(n) , and the maximum mass-specific power density of the energy conversion and/or actuation system(Ps) . A simple performance index is proposed by forming the product of these parameters

A.P = Es*n*Ps                    ------------- (1)

where A.P is called the actuation potential. Such a figure of merit is justified by the fact that a system with high power-source energy density, high conversion efficiency, and high actuator power density will be the lightest possible system capable of delivering a given amount of power and energy.    

 In the case of a battery-powered dc-motor-actuated robot, the energy density of the power source would be the electrical energy density of the battery, the conversion efficiency would be the combined efficiency of the (closed-loop controlled) dc motor and gear head, and the power density of the energy conversion and actuation system would be the rated output power of the motor/gear head divided by its mass. In the case of a gasoline-engine-powered hydraulically actuated system, the energy density of the power source would be the thermodynamic energy density of gasoline; the conversion efficiency would be the combined efficiency of the internal combustion engine(converting thermodynamic energy to shaft energy), hydraulic pump (converting shaft energy to hydraulic energy), and the hydraulic actuation system (converting hydraulic energy to controlled mechanical work); and finally, the power density of the energy conversion and actuation system would be the maximum output power of the hydraulic actuation system, divided by the combined mass of the engine, pump, accumulator, valves, cylinders, reservoir, and hydraulic fluid of the hydraulic system.

 With regard to this figure of merit, batteries and dc motors capable of providing the requisite power for a human scale robot offer reasonable conversion efficiency, but provide relatively low power-source energy density and a similarly low actuator/gear head power density. A gasoline-engine-powered hydraulically-actuated human-scale robot would provide a high power-source energy density, but a relatively low conversion efficiency and actuation system power density.

1.2. A Monopropellant Powered Approach

Liquid chemical fuels can provide energy densities significantly greater than power-comparable electrochemical batteries. The energy from these fuels, however, is released as heat, and the systems required to convert heat into controlled, actuated work are typically complex, heavy, and inefficient. One means of converting chemical energy into controlled, actuated work with a simple conversion process is to utilize a liquid monopropellant to generate a gas, which in turn can be utilized to power a pneumatic actuation system. Specifically, monopropellants are a class of fuels (technically propellants since oxidation does not occur) that rapidly decompose (or chemically react) in the presence of a catalytic material. Unlike combustion reactions, no ignition is required, and therefore the release of power can be controlled continuously and proportionally simply by controlling the flow rate of the liquid propellant. This results in a simple, low-weight energy converter system, which provides a good solution to the design tradeoffs between fuel energy density and system weight for the scale of interest.

Monopropellants, originally developed in Germany during World War II, have since been utilized in several applications involving power and propulsion, most notably to power gas turbine and rocket engines for underwater and aerospace vehicles. Modern day applications include torpedo propulsion, reaction control thrusters on a multitude of space vehicles, and auxiliary power turbo pumps for aerospace vehicles. This seminar describes the design of a monopropellant-powered actuation system appropriate for human-scale self-powered robots, and presents theoretical and experimental results that indicate the strong potential of this system for high energy density human-scale robot applications. Specifically, with regard to the figure of merit described before .The proposed approach is projected to provide a significantly greater power-source energy density and actuation power density relative to batteries and dc motors, and is projected to provide a higher conversion efficiency and significantly greater actuation system power density relative to a gasoline-powered hydraulic system.

2. DESCRIPTION OF MONOPROPELLANT ACTUATION SYSTEM

The monopropellant-powered actuation system is similar in several respects to a typical pneumatically actuated system, but rather than utilize a compressor to maintain a high-pressure reservoir, the proposed system utilizes the decomposition of hydrogen peroxide (H2O2) to pressurize a reservoir. Peroxide decomposes upon contact with a catalyst. This decomposition is a strongly exothermic reaction that produces water and oxygen in addition to heat. The heat, in turn, vaporizes the water and expands the resulting gaseous mixture of steam and oxygen. Since the liquid peroxide is stored at a high pressure, the resulting gaseous products are similarly at high pressure, and mechanical work can be extracted from the high-pressure gas in a standard pneumatic actuation fashion.

The conversion of stored chemical energy to controlled mechanical work takes place as follows. The liquid H2O2 is stored in a tank pressurized with inert gas (called a blow down tank) and metered through a catalyst pack by a solenoid-actuated control valve. Upon contact with the catalyst, the peroxide expands into oxygen gas and steam. The flow of peroxide is controlled to maintain a constant pressure in the reservoir, from which the gaseous products are then metered through a voice-coil-actuated four-way proportional spool valve to the actuator. Once the gas has exerted work on its environment, the lower energy hot gas mixture is exhausted to atmosphere.

3. MONOPROPELLANT ACTUATOR PROTOTYPE

3.1. Hardware

A prototype of the monopropellant-powered actuation system depicted in Fig. 1 was fabricated and integrated into a single degree-of-freedom manipulator, as shown in Fig. 2.
The primary objective of building the prototype was to demonstrate tracking control and to conduct experiments characterizing the actuation potential described by (1). The propellant is stored in a stainless steel blow down propellant tank, and is metered through a two-way solenoid-actuated fuel valve through a catalyst pack and into a stainless-steel reservoir. The catalyst pack consists of a 5-cm-long (2 in), 1.25-cm-diameter (0.5 in) stainless-steel tube packed with catalyst material. A pressure sensor measures the reservoir pressure for purposes of pressure regulation. The high-pressure hot gas is metered into and out of a 2.7 cm (1-1/16 in) inner diameter, 10 cm (3.9 in) stroke double-acting single-rod cylinder by a four-way spool valve, modified for proportional operation by replacing the solenoid actuator with a thermally isolated voice coil. The valve spool displacement is measured with a differential variable reluctance transducer (DVRT) in order to enable closed-loop control of the valve spool position. The pneumatic cylinder is kinematically arranged to produce a bicep-curling motion upon extension of the piston, as illustrated in Fig. 3.

3.2. Control

Control of the system is achieved using three separate control loops. The first and simplest is the pressure regulation of the reservoir. Pressure feedback from the pressure sensor switches the solenoid fuel valve with a thermostat-type on-off controller that regulates the reservoir pressure to 1515 kPa (220 psig). The second control loop provides a high-bandwidth (i.e., approximately10 Hz) position control of the valve spool. Finally, the valve spool position is commanded by an outer control loop, which controls the angular motion of the single-degree-of-freedom manipulator. The outer control loop utilizes a rotary potentiometer to provide arm angle measurement for a position, velocity, acceleration (PVA) feedback controller, which commands the valve spool position.

4. EXPERIMENTS

4.1. Load Profile

Since the actuator relies on gas as an energetic medium, and since the actuation system is not designed to utilize energy resulting from condensation of the steam (steam quality less than 100%), the energy required to vaporize the water will not be recovered and as a result the conversion efficiency is lower than if actuation system included partial condensation. The best possible efficiency would occur when partial condensation is allowed to occur within the actuator and also when the load profile of the piston is designed to allow isentropic expansion from high pressure down to the lowest pressure possible (atmospheric pressure). In particular the most efficient load profile is such that the expansion of the peroxide reaction products is isobaric until all propellant mass is in the actuator, at which point the expansion becomes isentropic and continues as such until the cylinder pressure reaches atmospheric. Partial condensation occurs as a result of this load profile, leaving 70% quality steam in the actuator. This load profile would yield a theoretical efficiency of 39 %( calculated theoretically) for the 70% peroxide solution at a supply pressure of 220 psig.

4.2. Uninsulated Experiments

Experiments were conducted to measure the previously calculated conversion efficiency. A 70% peroxide solution was used as the propellant to maintain acceptable temperatures for commercially available components. For these experiments, the single-degree-of-freedom manipulator was commanded to move the 11 kg mass through a 30-degree amplitude, 1-Hz sinusoidal motion. The work output was computed indirectly by measuring the angle and, in post-processing, computing the actuation torque using a model of the load. The instantaneous power and average power could then be calculated. The propellant mass consumption was measured indirectly by recording the pressure of the nitrogen gas in the blow down tank, assuming an isothermal process inside the constant-volume tank, and calculating the volume occupied by the nitrogen from the ideal gas equation, which in turn yields the volume of propellant in the tank. Since the propellant is a liquid, the mass of propellant used is easily computed from the known volume and density. The conversion efficiency is then computed over an integer number of cycles with the heat of decomposition of 70% hydrogen peroxide solution.

 Based on these measurements, the experimentally determined conversion efficiency was found to be 6.6%. Note that the electrical power required to operate the valves was neglected in this analysis. The measured average combined electrical power required by the fuel and gas valves was approximately 2 W. Since this is only about 3% of the average work delivered by the actuator, this electrical power can be legitimately omitted from the analysis. The significant discrepancy between the measured conversion efficiency of 6.6% and the calculated upper bound of 16% is due to two major factors. The first is inefficiency in control and the second is heat loss. Specifically, the thermodynamic model assumed that no gas was exhausted during a given monotonic segment of the trajectory, and that no energy was lost as heat. Regarding the former, any overshoot of the desired trajectory will violate the assumed monotonicity of the trajectory, and therefore will result in an intermittent exhaust of hot gas and a resulting decrease in the efficiency. The existence of such intermittent exhaust is evident in the oscillations exhibited in the power delivered to the load which is shown in Fig. 4 plotted against the theoretically required power .Regarding inefficiency due to heat loss, the external surfaces of the catalyst pack, reservoir, and actuator were hot during the experiments, thus indicating the presence of heat flow. In order to more quantitatively assess the degree of heat loss, the prototype was instrumented with thermocouples so that the rate of heat loss could be estimated from surface temperature measurements referenced to tables associated with heat loss from uninsulated steam piping . This measurement yielded an estimated heat loss rate of 140W. Note that the average measured mechanical power output was approximately 60 W. The prototype lost twice as much energy in the form of heat as it delivered in the form of work. Taking into account this heat loss, the conversion efficiency of the prototype was recalculated to be 10 %

4.3. Insulated Experiments

In order to improve the measured conversion efficiency, the catalyst pack, reservoir, and actuator were wrapped in insulating tape, as shown in Fig. 5, and measurement of the conversion efficiency was repeated. For the insulated case, the experimentally determined conversion efficiency was found to be 9 %.Thermocouple measurement of the surface temperatures, as previously described, yielded an estimated heat loss rate of 73 W, approximately half of the uninsulated case. Using this heat loss rate, the theoretically calculated efficiency was 12 %, the difference presumably due to control inefficiency (i.e., intermittent exhausts).

4.4. Experimentally Determined Actuation Potential

Having measured the conversion efficiency, the mass-specific power density of the actuator and the mass-specific energy density of the power source need to be determined in order to calculate the actuation potential (1). The former is found by determining the mass and the maximum output power of the energy conversion and actuation system. Though finding the mass is a trivial task, characterizing the maximum deliverable power is not as straightforward due to the dependence upon several factors, including the supply pressure, the valve flow coefficient of the proportional valve, and the nature of the load, among others. In order to base the actuator power density solely on measured data the maximum deliverable power was estimated by using the peak power consistently measured during the previously described efficiency experiments. As evidenced by the data in Fig. 4, the actuator can consistently generate peak power of 150W, as indicated by the dashed line overlaid on the plot. The mass of the actuation system was obtained by weighing the components of the actuator shown in Fig. 2. The mass of each component is summarized in Table 1

As indicated in the table, the total actuation system mass is 1.5 Kg, thus resulting in an actuation system power density of 100 W/Kg. This would increase for a multi-degree-of-freedom system, since such a system would only include a single fuel valve, catalyst pack, pressure reservoir, and pressure sensor. Having determined the actuator power density, only the power-source energy density need be found in order to calculate the actuator potential. As previously mentioned, the heat of decomposition of 70% hydrogen peroxide propellant is 2.0 MJ/Kg. The propellant must be stored, however, in a pressurized blow down propellant tank, and as such a legitimate characterization of the energy density should include the mass of a tank. Based on available data for a composite over wrapped propellant tank, the mass of a propellant tank for a volume on the order of 10 liters would conservatively decrease the mass-specific energy density of 70% peroxide from approximately 2.0 MJ/Kg to approximately 1.7 MJ/Kg. Based on this and the measured values of conversion efficiency and actuator power density previously described, the actuation potential for this single-degree-of-freedom system, as given by (1), would be 15.3 KJ KW/Kg2. As previously mentioned, the power density will increase for a multi-degree-of-freedom system, and thus so will the actuation potential. For a six-degree-of-freedom system, for example, the total actuation system mass would be 5.2 Kg, or 870 g per actuator. The reservoir used in the single-degree-of-freedom experiment was oversized, and is appropriately sized for a power-comparable six-degree-of-freedom system. The actuation system power density would therefore increase to 172 W/Kg, and the corresponding actuation potential to 26.4 KJ KW/Kg2 for the six-degree-of-freedom system.

 For purposes of comparison, the best commercially available rechargeable batteries have energy densities of approximately180 KJ/Kg (e.g., Evercel M40-12 nickel zinc, or SAFT 27 10 LAS silver zinc). A rare-earth permanent-magnet dc motor with a harmonic drive gear head with output characteristics capable of achieving the trajectory specified by Table I, has a power density of approximately 48 W/Kg. Note that this remains invariant, regardless of the number of degrees of freedom. Finally, one can assume that the overall conversion efficiency would be the combined efficiencies due to pulse width-modulation (PWM) control, the motor, and the gear head. The PWM efficiency was estimated to be 95%, the motor efficiency calculated for the desired trajectory to be 90% (i.e., the resistive power loss in the motor windings was calculated given the desired torque), and the harmonic drive gear head efficiency was estimated based on manufacturer data to be 65%. The resulting actuation potential for this type of system would therefore be 4.8 KJ KW/Kg. The poorly insulated single-degree-of-freedom experimental setup with 70% peroxide therefore exhibited an actuation potential more than three times a state-of-the-art battery/dc motor system. A similar six-degree-of-freedom system would exhibit an actuation potential over fives times the battery/dc motor system.

4.5. Projected Performance for High-Test Propellant

Though improvements can clearly be made with improved insulation and control performance, the most obvious means of improving the actuation system performance is to substitute a fully concentrated version of the propellant (i.e., 100%hydrogen peroxide) in place of the 70% solution used in the previously described experiments. Though procedurally quite simple, such experiments cannot be performed on commercially available pneumatic components, due to the high decomposition temperatures. Specifically, the adiabatic decomposition temperature of 100% peroxide is approximately 1000 0 C (1800 F), compared to approximately 230 0 C (450 F) for a 70% solution. Rather than conducting experiments using 100% peroxide, one can obtain a reasonable estimate of performance with projections based upon the experiments conducted with 70% solution. Upon replacing 70% propellant with 100% (technically 99.6%), at least two of the three parameters forming the actuation potential figure of merit would be expected to increase. Specifically, since the propellant contains more peroxide per unit mass, the heat of decomposition increases by a factor of 1.45 from 2.0 MJ/Kg to 2.9 MJ/Kg.

 Additionally, the relatively low conversion efficiencies observed earlier were primarily due to the heat required to vaporize the water in the reaction product. Since the 100% propellant contains less water, less energy is invested in vaporizing the reaction product. Recalculating the expected efficiencies accounting for the reduced water content, the conversion efficiency scales by a factor of 1.56. Assuming that the actuation system power density remains invariant (i.e., that it does not increase with the 100% propellant), the single-degree-of-freedom system shown in Fig. 2 with 100%propellant would be expected to have an actuation potential of 35 KJ KW/Kg2 , which is 7.3 times greater than the battery /dc motor system. A similar six-degree-of-freedom system would exhibit an actuation potential of 60.4 KJ KW/Kg2, more than an order of magnitude greater than the battery/dc motor system. The promise of such performance, which would presumably be further improved with better insulation and light weight components, justifies the fabrication of custom high-temperature pneumatic components.

5. CHALLENGES OF DESIGN

The biggest challenge in using monopropellant as a power source is providing adequate insulation to prevent the heat loss from the system. We have seen from the experimental results that the heat loss exceeds the power output obtained from the actuator. Finding a suitable method to contain this heat loss is the first and the biggest challenge in designing a monopropellant based power supply.

Another problem is the non availability of parts that can withstand the heat produced on the decomposition of 100% hydrogen peroxide. Due to this reason, a hydrogen peroxide solution of lower strength has to be used. Materials more resistant to heat are to be used to make the parts of the system so that it can withstand higher temperatures. This will aid the use of higher concentrations of peroxide thereby increasing the actuation potential of the system.

Monopropellants are highly reactive materials and are even toxic to humans. It has a tendency to catch fire if spilt on clothing. So the persons handling the fuel should be extremely cautious in order to avert possible danger of explosion and intoxication. The conventional power systems do not have such problems. Hence extra care must be taken while selecting the materials to be used in the system.

The selection or rejection of a proposed design depends heavily on its economic aspect. Hydrogen peroxide powered system when compared with battery operated power system is very costly in running condition. Also due to the presence of valves, maintenance costs of the system are high as well. The choice of valves can also influence the reliability of the system. The next challenge in designing monopropellant powered systems is attaining proper co ordination between the different control loops which controls the operation of the system. The emission of hot steam might be an inconvenience to other human workers if such robots are used along with humans. So it is better to limit the use of such robots to places inaccessible to humans. Controlling the emissions from the robot can make it usable along with humans. This can also improve the efficiency of the system.

6. CONCLUSION

A power supply and actuation system appropriate for a position or force controlled human-scale robot was proposed. The proposed approach utilizes a monopropellant as a gas generant to power pneumatic-type hot gas actuators. Experiments were performed that characterize the energetic behavior of the proposed system and offer the promise of an order-of-magnitude improvement in actuation potential relative to a battery powered dc-motor-actuated approach. Experiments also demonstrated good tracking and adequate bandwidth of the proposed actuation concept.

Steam powered robots are a possibility in the future provided the limitations of the existing prototype is done away with. A better actuation potential can be obtained by providing better insulation to the prototype thereby reducing the heat loss. Another challenge before researchers is to manufacture parts that can withstand the high temperatures generated on decomposition of 100% H2O2 .With the introduction of better controls, fuel and insulation, the se robots could function effectively and economically.

The proposed power supply was found to be a feasible solution to the problem of providing a long lasting power supply to robots that can actually work. Moreover the power output could be easily adjusted by controlling the rate of flow of the monopropellant. Although a full size human scale robot powered by a monopropellant is yet to be made, the experimental results obtained from a single degree of freedom manipulator proves the feasibility of such a system.

3G Technology

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                         3G refers to the next generation of wireless communications technology; it is a ‘catch all’ name which encompasses everything from the technology to the branding of mobile communication devices.  The aim of 3G (third generation) is to deliver the capability of much higher data rates to mobile communications devices over a large geographical area. Data rates of up to 2megabits per second will be capable in some areas.It is also the aim of 3G to unify the wireless devices the world over, so a user from the UK, can travel Europe, and the US, and use the same, highspeed data links, seamlessly as they travel the globe.  3G is a packet switched suite of protocols, a technology which was originally developed for the internet, it also uses techniques such as Code Division Multiple Access (originally developed by the military) to allow efficient, fast, and secure communications over the wireless medium. To the end user, 3G means fast World Wide Web browsing, file transfers, emailing, even video phoning and video conferencing from their mobile phone, PDA, or laptop. With coverage over all of Europe, the USA, China, Japan, and the rest of the world, with seamless integration between all of these countries and more. Although 3G is relatively an infant, the technology is growing fast, with more and more wireless technology companies developing devices with 3G capabilities, such as Nokia, Siemens and Sony Ericsson.On the horizon is 4G, a technology which will truly integrate the internet, and mobile telecommunications.


Evolution towards 3G

                                  Being called 3G, or third generation, there is, inevitably, a first and second generation.

                                  1G refers to the original analogue mobile phones, which resembled a brick. They were large, and very heavy, due to the weight of the battery, they were also very expensive. However, they paved the way for something that was soon to become a revolution in the technological world, phones would soon start to be smaller, lighter, cheaper, and better. Operating time increased while battery weight dropped, this was due to advancements in battery technology, as well as circuit design which allowed for much lower power consumption.
                                          2G saw the birth of the digital mobile phone, and a standard which is the greatest success story in the history of the mobile phone to date. The Global System for Mobile Communications (GSM) is a standard that unified Europe’s mobile phone technologies, it allows one phone to be used throughout Western Europe. Using TDMA (Time division multiple access), the GSM standard allowed millions of users throughout Europe to travel freely and still be able to use there phone. Although Europe enjoyed a unified standard, in America, three standards still exist, from three different companies. Because of this mobile communications haven’t become nearly as popular in the States, as they have done in Europe.2G worked well for voice communications, it provided data rates of up to 9.6Kbps, good enough for voice, but no where near enough for bandwidth demanding modern day media, such as Video and file transfers. Something which the world was screaming out for, and to provide this, 3G was developed.
                                          Due to the nature of 3G, and its incredible complexity and expensive, the move from 2G to 3G wasn’t going to happen over night, so the 2.5G standard was developed.
                                       The 2.5G standard had a major technically different feature compared to its predecessor, it used Packet Switching technology to transmit data. The General Packet Radio Service (GPRS) replaced GSM as the 2.5G standard. GPRS actually overlays a packet switched technology onto the original GSM circuit switched network. Data rates of 2.5G can reach 50kbps, some may think this is a waste of time, and service provides should have gone straight to the goal and implemented 3G, however, the 2.5G standard is a much needed step, as it gives service providers experience of running packet switched networks, and charging on a data bases, rather than a time basis.
                           Other than GPRS, another standard called EDGE is another upgrade option from GSM, and is three times faster with a maximum transfer rate of 150Kbps as opposed to GPRS’s 50Kbps. EDGE also can be an upgrade from TDMA networks, so some American operators may go this route.

How does 3G work?

                      3G is a packet switched technology, much like the internet. There are some basic principles of Radio Transmission Technologies (RTT’s) we need to understand before we can understand how 3G works, these are:

Simplex & Duplex, TDD & FDD, Symmetric & Asymmetric transmission, TDMA & FDMA, Circuit switching & packet switching and 3G geographical cells.

Simplex and Duplex

                        In a simplex transmission, information can only flow one way at one time, this is because there is only one frequency being used to communicate on. The easiest way of explaining this is to use walkie-talkies as an example. With a set of walkie-talkies, only one person can talk to the other at any given time, for the other person to transmit, they must wait until the other person has stopped.

                        In a duplex transmission, two data transmissions can be sent at any one time, this is how mobile phones work, it allows both people to speak at the same time, without any delay. If more than two data transmissions can happen at any one time, this is called multiplex.

TDD and FDD

                        Up until the recent developments of mobile phones, FDD (frequency division duplex) was used, this is where several frequencies are used, one for the upstream (signals going from the phone to the base station), and one for the downstream (the opposite, from the base station to the phone). A “guard band” is also needed, which sits in between the frequencies to separate them and provide isolation.
                        Although FDD works, it is very wasteful, as it uses several frequencies in total, and not to there full potential. This is why TDD was developed.

                        TDD means Time Division Duplex, and as the name suggests, this uses time, rather than frequency to do the duplexing, hence saving valuable frequencies. It works by switching the signals very rapidly. First the upstream transmits, then the downstream transmits and this continues to cycle, this happens so quick, it seems like the upstream and downstream are permanently connected. This gives the same end product as FDD, but uses much less frequencies. As with FDD, this also requires some sort of guard, but as we are duplexing in the time domain, it uses a guard time, rather than a guard frequency.

Symmetric and Asymmetric Transmission

                         A symmetric transmission is where the upstream, and downstream are the same speed, or data rate. Things such as voice on mobile phones use symmetric transmission, as the data rate needed to transmits your voice is the same as receiving another persons.
                         For things like video broadcasts, internet surfing etc, a lot more downstream bandwidth is required, as you will mostly be receiving data. Typically the only things being sent upstream in that case is requests (for instance, you clicking on a link in your wap/internet browser), or packet acknowledgments. A typical example of an Asymmetric connection is ADSL broadband, the A, which coincidently enough stands for Asymmetric, usually has 256Kbps of upstream, and 512+kbps on the downstream bandwidth.

 TDMA vs. CDMA

                        We have considered how a mobile phone can send and receive calls at the same time (via an uplink and a downlink). Now we will examine how many users can be multiplexed into the same channel (i.e., share the channel) without getting interference from other users, a capability called multiple access. For 3G technology, there are basically two competing technologies to achieve multiple access: TDMA and CDMA.

TDMA is Time Division Multiple Access. It works by dividing a single radio frequency into many small time slots. Each caller is assigned a specific time slot for transmission. Again, because of the rapid switching, each caller has the impression of having exclusive use of the channel.

CDMA is Code Division Multiple Access. CDMA works by giving each user a unique code. The signals from all the users can then be spread over a wide frequency band. The transmitting frequency for any one user is not fixed but is allowed to vary within the limits of the band. The receiver has knowledge of the sender's unique code, and is therefore able to extract the correct signal no matter what the frequency.

                        This technique of spreading a signal over a wide frequency band is known as spread spectrum. The advantage of spread spectrum is that it is resistant to interference - if a source of interference blocks one frequency, the signal can still get through on another frequency. Spread spectrum signals are therefore difficult to jam, and it is not surprising that this technology was developed for military uses.

                        Finally, let's consider another robust technology originally developed by the military which is finding application with 3G: packet switching.

Circuit Switching vs. Packet Switching

                        Traditional connections for voice communications require a physical path connecting the users at the two ends of the line, and that path stays open until the conversation ends. This method of connecting a transmitter and receiver by giving them exclusive access to a direct connection is called circuit switching.
                        Most modern networking technology is radically different from this traditional model because it uses packet data. Packet data is information which is:

o chopped into pieces (packets),
o given a destination address,
o mixed with other data from other sources,
o transmitted over a line with all the other data,
o reconstituted at the other end.

Packet-switched networks chop the telephone conversation into discrete "packets" of data like pieces in a jigsaw puzzle, and those pieces are reassembled to recreate the original conversation. Packet data was originally developed as the technology behind the Internet.
A data packet.

The major part of a packet's contents is reserved for the data to be transmitted. This part is called the payload. In general, the data to be transmitted is arbitrarily chopped-up into payloads of the same size. At the start of the packet is a smaller area called a header. The header is vital because the header contains the address of the packet's intended recipient. This means that packets from many different phone users can be mixed into the same transmission channel, and correctly sorted at the other end. There is no longer a need for a constant, exclusive, direct channel between the sender and the receiver.
                   Packet data is added to the channel only when there is something to send, and the user is only charged for the amount of data sent. For example, when reading a small article, the user will only pay for what's been sent or received. However, both the sender and the receiver get the impression of a communications channel which is "always on".
On the downside, packets can only be added to the channel where there is an empty slot in the channel, leading to the fact that a guaranteed speed cannot be given. The resultant delays pose a problem for voice transmission over packet networks, and is the reason why internet pages can be slow to load.

3G geographical cells

              The 3G network has a hierarchal network of different sized cells. These are:

                       
Ø  A Macro cell this is the biggest of the three areas, coverage is normally around the size of a city.
Ø  A Micro cell this cell has the coverage, of about the size of city centre.
Ø  A Pico cell The smallest coverage, perhaps a office complex, hotel, or airport. A Pico cell is often known as a “hot spot”.
                        The reason for the above division of regions is simple, shorter range communications are faster, and allow for a higher amount of users. This is why a Pico cell, or hot spot., is located to a small geographical area which is a very busy area, such as an airport.

                        TDD isn’t good in transmitting long distances, this is because of the delay. If you think, TDD uses time to duplex signals onto the same frequency. The further the mobile phone is away from the base station, the longer it takes a signal to travel, because it takes longer, there is more of a delay, so because of this the switching between time slots cannot happen so quick, so the useable bandwidth decreases.

2G Standards

                        The existing mobile phone market is referred to as the "second generation" of digital mobile communications, or "2G" (analogue mobile phones were "1G"). The European market is controlled by the Global System for Mobile communications (GSM) digital wireless standard. This uses TDMA as its radio transmission technology (RTT). GSM has proven to be the great success story of mobile standards as it has become the unifying standard in Europe - it is possible to use one phone throughout Western Europe. Because of the number of wireless users are in Europe this has greatly strengthened GSM's position as the basis for a potential global standard. The hegemony of GSM has resulted in Finland's Nokia and the UK's Vodafone becoming the powerhouses of the wireless economy.
                              In North America the situation is not nearly so unified. The situation is divided three-ways between GSM, a TDMA-based system from AT&T Wireless (IS-136), and a CDMA system called CDMAone (IS-95A) from Sprint and Verizon. This confusion of standards has resulted in the reduced popularity of cellphones in the US. CDMAone has perhaps the strongest grip on the American market, as well as being popular in Asia.

2G data transmission rates do not exceed 9.6Kbps (kilobits per second). This is not nearly fast enough to achieve complex 3G functionality.

2.5G Standards

                        The transition from 2G to 3G is technically extremely challenging (requiring the development of radically new transmission technologies), and highly expensive (requiring vast capital outlay on new infrastructure). For both of these reasons it makes sense to move to 3G via intermediate 2.5G standards.
                        2.5G radio transmission technology is radically different from 2G technology because it uses packet switching. GPRS (General Packet Radio Service) is the European 2.5G standard, the upgrade from GSM. GPRS overlays a packet-switched architecture onto the GSM circuit-switched architecture. It is a useful evolutionary step on the road to 3G because it gives telecoms operators experience of operating packet networks, and charging for packet data. Data transfer rates will reach 50Kbps.
                        EDGE (Enhanced Data for Global Evolution) is another 2.5G upgrade path from GSM. EDGE is attractive for American operators as it is possible to upgrade to EDGE from both TDMA (IS-136) networks as well as from GSM. You might see the full EGDE standard referred to as UWC-136.
                        EDGE data rates are three times faster than GPRS. Realistically, the maximum rate that EDGE will be able to achieve will be 150Kbps. Even so, EDGE might be used for some pseudo-3G networks (the minimum cut-off data rate for 3G systems is 144Kbps) though this is not generally regarded as a bona fide 3G solution.
                        As EDGE would be cheaper than a full-blown 3G solution, this makes it attractive, especially for operators which cannot afford a licence for the full 3G radio spectrum. Most notably, AT&T has announced it is to use EDGE. AT&T has claimed a maximum data rate of 384Kbps for EDGE, although experts point out that "this is based on the ideal scenario of one person using the network standing next to a base station". AT&T's wireless division, after receiving a $9.8 billion stake from Japan's NTT DoCoMo i-mode service, plans to overlay the 3G standard, W-CDMA, onto their EDGE networks in the American market.
                        Deploying EDGE might prove surprisingly complex - it's more than just a software upgrade. It may require additions to the hardware subsystems of base stations, changes to base station antennas, and possibly require the construction of new base stations. For these reasons, some GSM operators might not adopt EDGE but might migrate from GSM or GPRS directly to the 3G standard (W-CDMA).
                        The 2.5G upgrade from CDMAone (IS-95A) is to CDMAone (IS-95B) which adds packet-switched capability. It offers data rates up to 115Kbps.

3G Standards

                        The 3G standard was created by the International Telecommunication Union (ITU) and is called IMT-2000. The aim of IMT-2000 is to harmonize worldwide 3G systems to provide global roaming. However, as was explained in the introduction to this section, harmonizing so many different standards proved extremely difficult. As a result, what we have been left with is five different standards grouped together under the IMT-2000 label:

W-CDMA
CDMA2000
TD-CDMA/TD-SCDMA
DECT
UWC-136

At this point, the definition of what is and what isn't "3G" becomes somewhat murky. Of these five standards, only three allow full network coverage over macro cells, micro cells and pico cells and can thus be considered as full 3G solutions: W-CDMA, CDMA2000, and TD-SCDMA. Of the remainder, DECT is used for those cordless phones you have in the house, and could be used for 3G short-range "hot-spots" (hence, it could be considered as being "part of a 3G network"), but it does not allow full network coverage so is not considered further here. And UWC-136 is another name for EDGE which is generally considered to be a 2.5G solution and was considered in the previous section.
So that leaves W-CDMA, CDMA2000, and TD-SCDMA - the bona fide 3G solutions.

W-CDMA

                        The 3G standard that has been agreed for Europe and Japan (very important markets) is known as UMTS. UMTS is an upgrade from GSM via GPRS or EDGE. UMTS is the European vision of 3G, and has been sold as the successor to the ultra-successful GSM.
                        The terrestrial part of UMTS (i.e., non-satellite) is known as UTRA (UMTS Terrestrial Radio Access). The FDD component of UTRA is based on the W-CDMA standard  (UTRA FDD). This offers very high (theoretical!) data rates up to 2Mbit/sec.The TDD component of UTRA is called TD-CDMA (or UTRA TDD) and will be considered later.
                         The standardisation work for UMTS is being carried-out under the supervision of the Third Generation Partnership Project (3GPP).W-CDMA has recently been renamed 3GSM.

CDMA 2000

                       The chief competitor to Europe's UMTS standard is San Diego-based Qualcomm's CDMA2000.The standardisation work for CDMA2000 is being carried-out under the supervision of the Third Generation Partnership Project 2, (3GPP2). The CDMA Development Group offers advice to 3GPP2.
                        Even though "W-CDMA" and "CDMA2000" both have "CDMA" in their names, they are completely different systems using different technologies. However, it is hoped that mobile devices using the two systems will be able to talk to each other.
                        CDMA2000 has two phases: phase one is 1XRTT (144 Kbps) (also known as 1X). The next evolutionary step is to the two CDMA2000 1X EV ("EV" = "Evolution") standards. CDMA2000 1X EV-DO ("Data Only") will use separate frequencies for data and voice. The following step is to CDMA2000 1X EV-DV ("Data and Voice") which will integrate voice and data on the same frequency band.
                        South Korea's SK Telecom launched the world's first 3G system in October 2000. Their system is based on CDMA2000 1X. They were followed by LG Telecom and KT Freetel (both Korean). Operational 3G systems based on CDMA2000 1X are now appearing around the world.
                        In the USA, Sprint has launched its nationwide CDMA2000 1X service called “Sprint Power Vision”. With Sprint PCS Vision Multimedia Services, customers get streaming audio and video content from familiar sources, including ABC News Now, NFL Network, Fox Sports, ESPN, NBC Discovery Channel, and many more. Sprint offer a range of multimedia phones including the Fusic.

TD-CDMA/TD-SCDMA

                        The UMTS standard also contains another radio transmission standard which is rarely mentioned: TD-CDMA (TDD UTRA because it is the TDD component of UTRA). TD-CDMA was developed by Siemens. While W-CDMA is an FDD technology (requiring paired spectrum), TD-CDMA is a TDD technology and thus can use unpaired spectrum. TDD is well-suited to the transmission of internet data.
                        China has more mobile phone users than any other country in the world, so anything China does in 3G cannot be ignored. The Chinese national 3G standard is a TDD standard similar to TD-CDMA: TD-SCDMA. TD-SCDMA was developed by the China Academy of Telecommunications Technology (CATT) in collaboration with Siemens. TD-SCDMA eliminates the uplink/downlink interference which affects other TDD methods by applying "terminal synchonisation" techniques (the "S" in TD-SCDMA stands for "synchronisation"). Because of this, TD-SCDMA allows full network coverage over macro cells, micro cells, and pico cells. Hence, TD-SCDMA stands alongside W-CDMA and CDMA2000 as a fully-fledged 3G standard. The 3GPP have extended the TD-CDMA standard to include TD-SCDMA as an official IMT-2000 standard.
                        Unfortunately, TD-SCDMA has performed poorly in trials, and Chinese network operators may prefer W-CDMA over TD-SCDMA.

3G Applications:

Ø Wireless Internet
Ø Audio on demand
Ø Electronic postcards
Ø Video conferencing
Ø Secure mobile commerce transactions
Ø Traffic and traveling information - location specific
Ø Information services:
o Games
o E-mail
o Sports
o News Public transport
o Entertainment/gambling
o Job adverts
Ø Video telephony: Point-to-point video services
Ø On-line game:
o Download
o Rentals
o Review and tips/cheats
Ø Live & archive video:
o Short clips
o Information
o Entertainment

The 3G Performance Advantage :
      Time to download a 1 MB file:

Fixed line modem: 3 minutes
GSM cell phone: 15 minutes
Enhanced GSM phone: 1-5 minutes
3G phone (outdoor): 21 seconds
3G phone (indoor): 4 seconds
Bandwidth and speed:
                        3G promises increased bandwidth, up to 384 Kbps when a device is stationary or moving at pedestrian speed, 128 Kbps in a car, and 2 Mbps in fixed applications. It is expected that IMT-2000 will provide higher transmission rates: a minimum speed of 2Mbit/s and maximum of 14.4Mbit/s for stationary users, and 348 kbit/s in a moving vehicle

The Future of 3G:
                        There’s no doubt what is wanted for the future of 3G, and that’s convergence. Leading 3G figureheads around the world want a convergence of the phone networks, to unite the world as a whole with a wireless technology that is compatible across the globe.

                        There’s a good chance this will happen, as it has already begun to. And it possible won’t be far off that we see perhaps a sub-standard introduced that converges the different 3G standards into one global roaming capable standard.

                        On the horizon is 4G, which promises to bring true convergence of internet’s IP protocol technology to mobiles. By the time 4G is distributed, IPv6 will be well on its way, and the possibilities will be endless. Ever thought about texting your boiler to tell it to get the heating on just as you leave work?

3G Summary :
                        3G mobile is a major opportunity for business, commerce and consumers.Brings together the two fastest growing market sectors - Mobile and Internet Market.Services and standards evolving from 2G to 3G Significant opportunities for value added content and service providers.

Ad hoc networks

Recent advances in portable computing and wireless technologies are opening up exciting possibilities for the future of wireless mobile networking. A mobile ad hoc network (MANET) is an autonomous system of mobile hosts connected by wireless links. Mobile networks can be classified into infrastructure networks and mobile ad hoc networks according to their dependence on fixed infrastructures. In an infrastructure mobile network, mobile nodes have wired access points (or base stations) within their transmission range.
The access points compose the backbone for an infrastructure network. In contrast, mobile ad hoc networks are autonomously self-organized networks without infrastructure support. In a mobile ad hoc network, nodes move arbitrarily, therefore the network may experiences rapid and unpredictable topology changes. Additionally, because nodes in a mobile ad hoc network normally have limited transmission ranges, some nodes cannot communicate directly with each other. Hence, routing paths in mobile ad hoc networks potentially contain multiple hops, and every node in mobile ad hoc networks has the responsibility to act as a router.
Mobile ad hoc networks originated from the DARPA Packet Radio Network (PRNet) and SURAN project. Being independent on pre-established infrastructure, mobile ad hoc networks have advantages such as rapid and ease of deployment, improved flexibility and reduced costs.

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Multicasting is the transmission of datagrams to a group of hosts identified by a single destination address and hence is intended for group-oriented computing. In MANETs, multicasting can support a variety of applications such as conferences, meetings, lecturers, traffic control, search and rescue, disaster recovery, and automated battlefield. In ad hoc networks, each host must act as a router since routes are mostly multihop.
Figure 1-1 shows an example of using MANET to hold conference meeting in a company. A group of mobile device users set up a meeting outside their normal office environment where the business network infrastructure is missing. The mobile devices automatically construct a mobile ad hoc network through wireless links and   communicate with one another. The figure shows topology of the network and the available wireless links at a certain time. Suppose Susan wants to send data to Jerry. According to the network topology, Jerry’s PDA is not in the immediate radio transmission range of Susan’s laptop. The routing software on Susan’s laptop finds a route Susan �� Tommy �� Jerry and sends the data packets to Tommy’s laptop. Then Tommy’s laptop forwards the packets to the destination, Jerry’s PDA. If the network topology changes and the wireless link between Susan and Tommy become broken, the routing software on Susan’s laptop will try to find another route.

Well established routing protocols do exist to offer efficient multicasting service in conventional wired networks. These protocols, having been designed for fixed networks, may fail to keep up with node movements and frequent topology changes in a MANET. As nodes become increasingly mobile, these protocols need to evolve to provide efficient service in the new environment. Therefore, adopting existing wired multicast protocols as such to a MANET, which completely lacks infrastructure, appears less promising. So new protocols need to be proposed and investigated so that they take issues like topological change. Ad hoc network may consist of unidirectional links as well as bidirectional links. Moreover, wireless channel bandwidth is limited. The scarce bandwidth decreases even further due to the effects of multiple access, signal interference, and channel fading. Securing Adhoc routing presents challenges because the constrains in Adhoc networks usually arise due to low computational and bandwidth capacity of the nodes, mobility of intermediate nodes in an established path and absence of routing infrastructure. All these limitations and constraints make multihop mobile ad hoc network research more challenging.

   1.2 Challenges in Routing and Multicasting
         Routes in ad hoc networks are multihop because of the limited propagation range of wireless nodes. Since nodes in the network move freely and randomly, routes often get disconnected. Routing protocols are thus responsible for maintaining and reconstructing the routes in a timely manner as well as establishing the robust routes. Furthermore, routing protocols are required to perform all the above tasks without generating excessive control message overhead. Control packets must be utilized efficiently to deliver data packets, and be generated only when necessary. Reducing the control overhead can make the routing protocol efficient in bandwidth and energy consumption.
Multipoint communications have emerged as one of the most researched areas in the field of networking. As the technology and popularity of Internet grow, applications, such as online gaming, video conferencing, that require multicast support are become more widespread. In a typical ad hoc environment, network hosts work in groups to carry out a given task. Therefore, multicast plays an important role in ad hoc networks. As we can see, providing efficient multicasting over MANET faces many challenges, including dynamic group establishment and constant update of delivery path due to node movement. Multicast protocols used in static networks like Distance Vector Multicast Routing Protocol (DVMRP), Multicast Open Shortest Path First (MOSPF), and Core Based Tree (CBT) do not perform well in wireless ad hoc networks because multicast tree structures are fragile and must be readjusted as connectivity changes. Hence, the tree structures used in static networks must be modified, or a different topology between members (i.e., mesh) need to be deployed for efficient multicasting in wireless mobile ad hoc networks [1]. Undoubtedly, multicast communication is an efficient means of supporting group oriented applications. This is especially true in MANETs where nodes are energy-and bandwidth limited. In these resources constrained environments, reliable point –to-point protocols can get prohibitively expensive. The Convergence of multiple requests to a single node typically causes intolerable congestion, violating the time constraints of a critical mission, and may drain the node’s battery, cutting short the network’s lifetime. Despite the fact that reliable multicasting is vital to the success of mission critical applications in MANETs.

1.2.1          Dynamic Topologies
Wireless nodes in an ad-hoc network are free to move about at will. As such, the topology of the network, which is typically multi-hop, is highly dynamic, changing randomly at unpredictable intervals in unpredictable ways. Because of wireless radio propagation effects, such as interference, links may be either bidirectional or unidirectional.

1.2.2 Bandwidth-constrained, variable capacity links
The bandwidth capacity of wireless networks will remain significantly below that of their wired counterparts. The realizable throughput of wireless links above the data link layer, due to effects such as noise, fading, interference, and the inability to use collision detection for media access control is often significantly less than the radio’s maximum throughput at the physical layer. The effects of this, and given that users of ad-hoc networks will demand similar high-bandwidth services to those on wired networks, means that congestion on wireless networks will be much more common than in wired networks.

1.2.3 Energy-constrained operation
Wireless networks will typically operate on laptop computers, hand-held computers and other battery-powered devices. As such, ad-hoc routing protocols must be designed with the conservation of the device’s energy in mind. There is a conflict between the requirements that nodes in an ad-hoc network must be willing to offer their services for forwarding packets for other nodes, versus the desirability from an energy conservation perspective that nodes sleep when they are not actively being used.

1.2.4   Limited physical security
There is an increased possibility of eaves-dropping, spoofing, and denial-of-service attacks on wireless networks, due in part to their relative lack of physical security in relation to their wired counterparts. Security enhanced versions of ad-hoc routing protocols could be used to ensure the operation of the routing protocol remains unaffected by attempts to forge or alter routing protocol control messages. Care must be taken when transferring sensitive data across an ad-hoc network. This could be achieved by conventional encryption. However, Public Key Infrastructure (PKI), or more basic key exchange techniques are difficult in an ad hoc network due to the lack of authorities of trust and appropriate network infrastructure.

1.2.5 Zero Configurations
Another desirable property of ad-hoc networks is that they should require little or no administrative overhead for their operation. It is desirable that when a group of Wireless nodes come together, they can negotiate all the relevant networking parameters automatically without manual intervention. In IP-enabled ad-hoc networks, the most important parameter is a node’s Internet Protocol (IP) address. This issue of assigning unique IP addresses to nodes in an ad-hoc network is another area of substantial research. Traditional wired networks typically use a centralized solution to the problem in the form of the Dynamic Host Configuration Protocol (DHCP). Given the lack of a central administrative body in an ad-hoc network, a distributed approach is required. It is likely the solution will involve nodes selecting their IP address at random, and using some means, such as examining Address Resolution Protocol (ARP) traffic from other nodes, to prevent or resolve issues where collisions have occurred.


1.3   Contributions

The accomplishments, which are elaborated throughout this dissertation, can be broadly listed as follows:

A performed simulation of up to 50 seeds where each seed contains 100 nodes and evaluated ad hoc routing protocol scalability. Several schemes were introduced to improve the protocol performance in large networks. This work is the first to conduct a simulation study of such size using Qualnet 4.0 and NS 2.27.
Proposed the On-Demand Multicast Routing Protocol (ODMRP). ODMRP builds the mesh structure on demand to provide multiple paths among multicast members. The mesh makes the protocol robust to mobility. ODMRP can function as multicast and unicast.  The protocol was implemented in simulation platform using GloMoSim and Qualnet 4.0.
Applied various techniques to enhance the performance of ODMRP. Theses enhancements include mobility predictions, reliable packet delivery, and elimination of the route acquisition latency.
Studied the various QoS requirements with multicast routing in ad hoc networks and proposed a new cross-layer framework which provides QoS guarantee to multicast routing in MANETs. These QoS parameters include call-admission, bandwidth reservation and delay constraint.
Developed and implemented an Adhoc QoS multicasting (AQM) algorithm and proposed a cross layer framework to support QoS multicasting. This work is the first to provide multicast quality of service in mobile ad hoc networks.
Proposed ReAct transport layer protocol on top of the multicast zone routing protocol to provide reliable services. Achieved good scalability and high throughput by employing local recovery mechanism. The protocol was implemented in simulation platform using Qualnet 4.0.
The problem of constructing energy-efficient key distribution schemes for securing multicast communication in wireless ad hoc networks was studied. The network topology, the power proximity and the path loss characteristics of the medium were incorporated in the key distribution tree design to conserve energy. The algorithm has been developed for homogeneous environment.
1.5   Related Work
 1.5.1   Classification of Ad-hoc Routing Protocols
Ad-hoc routing protocols can broadly be classified into proactive, reactive and hybrid protocols. The approaches involve a trade-off between the amount of overhead required to maintain routes between node pairs (possibly pairs that will never communicate), and the latency involved in discovering new routes as needed.

1.5.1.1   Proactive Protocols
Proactive protocols, also known as table-driven protocols, involve attempting to maintain routes between nodes in the network at all times, including when the routes are not currently being used. Updates to the individual links within the networks are propagated to all nodes or a relevant subset of nodes, in the network such that all nodes in the network eventually share a consistent view of the state of the network. The advantage of this approach is that there is little or no latency involved when a node wishes to begin communicating with an arbitrary node that it has not yet been in communication with. The disadvantage is that the control message overhead of maintaining all routes within the network can rapidly overwhelm the capacity of the network in very large networks, or situations of high mobility. Examples of pro-active protocols include the Destination Sequenced Distance Vector (DSDV), and Optimized Link State Routing (OLSR).

1.5.1.2   Reactive Protocols
Reactive protocols, also known as on-demand protocols, involve searching for routes to other nodes only as they are needed. A route discovery process is invoked when a node wishes to communicate with another node for which it has no route table entry. When a route is discovered, it is maintained only for as long as it is needed by a route maintenance process. Inactive routes are purged at regular intervals. Reactive protocols have the advantage of being more scalable than table-driven protocols. They require less control traffic to maintain routes that are not in use than in table-driven methods. The disadvantage of these methods is that an additional latency is incurred in order to discover a route to a node for which there is no entry in the route table. Dynamic Source Routing (DSR) and the Ad-hoc On-demand Distance Vector Routing (AODV)  protocol are examples of on-demand protocols.

1.5.1.3   Hybrid Protocols
There exists another class of ad-hoc routing protocols, such as the Zone Routing Protocol (ZRP), which employs a combination of proactive and reactive methods. The Zone Routing Protocols maintains groups of nodes in which routing between members within a zone is via proactive methods, and routing between different groups of nodes is via reactive methods.

1.5.1.4   Multicast Routing Protocols
One Straightforward way to provide multicast in a MANET is through flooding. With this approach, data packets are sent throughout the MANET, and every node that receives this packet broadcasts it to all its immediate neighbor nodes exactly once. It is suggested that in a highly mobile ad hoc network, flooding of the whole network may be a feasible alternative for reliable multicast. However, this approach has considerable overhead since a number of duplicated packets are sent and packet collisions do occur in a multiple access based MANET . Furthermore, multicast routing protocols are classified into four categories based on how routes are created to the members of the group:
      Tree-based approaches
      Mesh-based approaches
      Stateless multicast
      Hybrid approaches
Tree-based multicast is a very well established concept in wired networks. Protocols such as Ad hoc Multicast Routing Protocol Utilizing Increasing ID Numbers (AMRIS), Multicast Ad hoc On-Demand Distance Vector (MAODV), Lightweight Adaptive Multicast (LAM), and Location Guided Tree Construction Algorithm for Small Group Multicast are belonging to this category.
In contrast to a tree-based approach, mesh-based multicast protocols may have multiple paths between any source and receiver pair. Protocols such as On-Demand Multicast Routing Protocol (ODMRP), Dynamic Source Routing (DSR), and Temporarily Ordered Routing Algorithm (TORA) are belonging to this category.
Tree and Mesh based approaches have an overhead of creating and maintaining the delivery tree/mesh with time. In a MANET environment, frequent movement of mobile nodes considerably increases the overhead in maintaining the delivery tree/mesh. To minimize the effect of such a problem, stateless multicast is proposed wherein a source explicitly mentions the list of destinations in the packet header. Stateless multicast focuses on small group multicast. Protocol Differential Destination Multicast (DDM) is belongs to this approach .
The tree-based approaches provide high data forwarding efficiency at the expense of low robustness, whereas mesh based approaches provide better robustness at the expense of higher forwarding overhead and increased network load. The hybrid approach combines the advantage of both approaches. Protocols such as Ad hoc Multicast Routing Protocol (AMRoute), Multicast Core Extraction Distributed Ad hoc Routing (MCEDAR) are belonging to this category.

Delay Analysis and Optimality of Scheduling Policies for Multi-Hop Wireless Networks

We analyze the delay performance of a multi-hop wireless network in which the routes between source-destination pairs are fixed. We develop a new queue grouping technique to handle the complex correlations of the service process resulting from the multi-hop nature of the flows and their mutual sharing of the wireless medium. A general set based interference model is assumed that imposes constraints on links that can be served simultaneously at any given time. These interference constraints are used to obtain a fundamental lower bound on the delay performance of any scheduling policy for the system.
We present a systematic methodology to derive such lower bounds. For a special wireless system, namely the clique, we design a policy that is sample path delay optimal. For the tandem queue network, where the delay optimal policy is known, the expected delay of the optimal policy numerically coincides with the lower bound. The lower bound analysis provides useful insights into the design and analysis of optimal or nearly optimal scheduling policies.

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EXISTING SYSTEM:
       
                    A large number of studies on multi-hop wireless networks have been devoted to system stability while maximizing metrics like throughput or utility. These metrics measure the performance of a system over a long time-scale. The delay performance of wireless networks, however, has largely been an open problem. This problem is notoriously difficult even in the context of wire line networks, primarily because of the complex interactions in the network (e.g., superposition, routing, departure, etc.) The problem is further exacerbated by the mutual interference inherent in wireless networks which, complicates both the scheduling mechanisms and their analysis.

 Disadvantages:
1.     Simultaneity
2.     Throughput
3.     Resource allocation


PROPOSED SYSTEM:
             
               We analyze a multi-hop wireless network with multiple source-destination pairs, given routing and traffic information. Each source injects packets in the network, which traverses through the network until it reaches the destination. A packet is queued at each node in its path where it waits for an opportunity to be transmitted. The delay performance of any scheduling policy is primarily limited by the interference, which causes many bottlenecks to be formed in the network. We develop new analytical techniques that focus on the queuing due to the (K, X)-bottlenecks. One of the techniques, which we call the “reduction technique”, simplifies the analysis of the queuing upstream of a (K, X)-bottleneck to the study of a single queue system with K servers.

Advantages:
1.     Single Queue System
2.     Back Pressure Policy
3.     Saving s of time


MODULES:
   
1.     Characteristics of Bottlenecks
2.     Reduction Technique
3.     Reduced System
4.     Bound on expected delay
5.     Design of delay efficient policies

1. Characteristics of bottlenecks in the system
             
                    Link interference causes certain bottlenecks to be formed in
the system. We define a (K, X)-bottleneck to be a set of links
X ⊂ L such that no more than K of its links can be scheduled
Simultaneously.


2. Reduction Technique

                    We describe our methodology to derive lower bounds on the average size of the queues corresponding to the flows that pass through a (K, X)-bottleneck.


3. Reduced System
               
                   Consider a system with a single server and AX(t) as the input. The server serves at most K packets from the queue. Let QX(t) be the queue length of this system at time t. Flows II, IV and VI pass through an exclusive set using two, three and two hops of the exclusive set respectively. The corresponding G/D/1 system is fed by the exogenous arrival streams 2AII (t), 3AIV (t) and 2AV I (t).
4. Bound on Expected Delay
 
               
                 We now present a lower bound on the expected delay of the flows passing through the bottleneck as a simple function of the expected delay of the reduced system. In the analysis, we use above Theorem to bound the queuing upstream of the bottleneck and a simple bound on the queueing downstream of the bottleneck. Applying Little’s law on the complete system, we derive a lower bound on the expected delay of the flows passing through the bottleneck.

5. Design of delay efficient policies

               
                 A scheduler must satisfy the following properties.      
                 
• Ensure high throughput:  This is important because if the scheduling policy does not guarantee high throughput then the delay may become infinite under heavy loading.

• Allocate resources equitably: The network resources must be shared among the flows so as not to starve some of the flows. Also, non-interfering links in the network have to be scheduled such that certain links are not starved for service. Starvation leads to an increase in the average delay in the system.  
                           
CONCLUSION:
             
             Thus, new approaches are required to address the delay problem in multi-hop wireless systems. To this end, we develop a new approach to reduce the bottlenecks in a multi-hop wireless to single queue systems to
Carry out lower bound analysis.
                    The analysis is very general and admits a large class of arrival processes. Also, the analysis can be readily extended to handle channel variations. The main difficulty however is in identifying the bottlenecks in the system. The lower bound not only helps us identify near-optimal policies, but may also help in the design of a delay-efficient policy

STORAGE AREA NETWORKS

Many organisations, including those in the HE/FE sector are finding that storage growth is increasing at an alarming rate and, when combined with a trend to require more servers to support storage, is leading to an unmanageable situation as far as storage management is concerned. The growth of distributed systems is also giving concern in many organisations as standards of support in a devolved environment are not always adequate.  Consequently, consolidation of both servers and storage is looking very attractive.


Networked storage solutions (of which SANs and NAS are examples – see below) can offer increased flexibility for connecting storage, ensuring much greater utilisation of disk storage space and support for server consolidation (as storage and server capacity growth trends are no longer linked).

Installing a SAN is large and complicated undertaking, needing institutional management commitment and is more suited to environments where a large proportion of the institution’s data will reside on the SAN.  NAS can provide “plug and go” solutions for file serving, but SANs are better able to support large corporate databases and provide enhanced resilience.

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1.0                  The Technology
1.1                    Defining the Storage Technology: DAS, SAN, NAS
Traditionally, data storage resides on hard disks that are locally attached to individual servers. This is known as Direct Attached Storage (DAS). Although this storage may now be large (in the order of 100s of Gigabytes of data storage per server) the storage is generally only accessible from the server to which it is attached. As such, much of this disk space remains unused and plenty of ‘contingency’ has to be built into storage needs when determining server specification. In addition, if the server were to fail, access to the data held on those local disks is generally lost.

A Storage Area Network (SAN) is a separate “network” dedicated to storage devices and at minimum consists of one (or more) large banks of disks mounted in racks that provide for ‘shared’ storage space which is accessible by many servers/systems. Other devices, such as robotic tape libraries may be attached to the SAN.  See Figure 1 for a representation of both DAS and SAN storage.

Network Attached Storage (NAS) is storage that sits on the ordinary network (or LAN) and is accessible by devices (servers and workstations) attached to that LAN.  NAS devices provide access to file systems and as such are effectively file server appliances.  Delivery of file systems is most commonly via NFS (Network File System) or CIFS (Common Internet File System) protocols, but others may be used e.g. NCP (NetWare Core Protocol).  These file systems require some sort of associated authentication system to check permissions for file access.

A SAN functions as a high-speed network similar to a conventional local area network (LAN) and establishes a direct connection between storage resources and the file server infrastructure. The SAN effectively acts as an “extended storage bus” using the same networking elements of a LAN including routers, bridges, hubs and switches. Thus, servers and storage can be ‘de-coupled’ allowing the storage disks to be located away from their host servers.  The SAN is effectively transparent to the server operating system, which “sees” the SAN attached disks as if they were local SCSI disks.  Figure 1 also shows the attachment of storage arrays and tape libraries via switches.
                                                                     
A dedicated SAN carries only “storage data”. This data can be shared with multiple servers without being subject to the bandwidth constraints of the “normal network” (LAN). Practically, a SAN allows for data to be managed centrally and to assign storage “chunks” to host systems as required.

The main benefit of NAS devices is ease of deployment - most devices offering a “plug and play” capability, being designed as single purpose “appliances”. Modern NAS appliances can also serve large amounts of data with internal storage capacity measured in Terabytes.  Some NAS appliances are limited by the authentication schemes supported and NetWare users in particular should seek clarification from vendors over compatibility issues.

Many regard SAN and NAS as competitors, but in reality they are complementary technologies – SAN delivering effective block-based input/output, whilst NAS excels at file based input/output (usually via NFS or CIFS).  A hybrid device called a NAS Head or a NAS Gateway has storage that resides in the storage arrays attached to a SAN whilst still delivering file systems over the LAN.  A combination of a SAN with NAS Gateways may be an effective way for sites to deliver file-based functionality e.g. for user home directories.

In fact, DAS still has an ongoing use for many purposes – the cost of connecting servers to the SAN can be high and for systems like DNS servers, for example, where redundancy is provided by other means (multiple equivalent servers), then highly critical data can be resident on the direct attached disks of the servers.

The world of storage is rapidly changing and interested parties are advised to keep monitoring useful storage-related web sites [1].
1.2                    The Fabric – Switches, Fibre Channel, iSCSI technologies
The fabric for a SAN provides the connectivity between the host servers and the storage devices.  The dominant architecture for SANs is based on Fibre Channel (FC) [2], that whilst expensive, does have advantages in terms of its connectivity options.  Compared to SCSI devices, for example, many more storage devices may be connected over much larger distances with higher data transfer rates.

Cables to connect SAN components are of three types: copper, short-wave fibre or long-wave fibre. Copper cables are only suitable for short connections (less than 12m), whilst short-wave fibre (multi-mode 50 micron) is used for distances up to 500m with long-wave fibre (single-mode 9 micron) needed for longer distances up to 10 Km [3].  A Fibre Channel transceiver unit called a GBIC (Gigabit Interface Connector) is then needed to connect the FC cables to the FC devices.  Two types of GBIC are available: short-wave (for distances up to 500m) or long-wave (for distances up to 10Km) [4].

In Fibre Channel topologies the host server may be connected via a Host Bus Adapter (HBA) to the storage directly, via a hub or a switch.  Direct connections to storage do not constitute a “network” and so are not used in SANs.  Hubs use a topology known as Fibre Channel Arbitrated Loop (FC-AL) that shares the loop’s total bandwidth amongst all attached FC devices with a total device restriction of 126 attached FC devices.   Switches provide a set of multiple dedicated, fully-interconnected, non-blocking data paths known as a “fabric”.

Switches provide simultaneous routing of device traffic and are capable of supporting a theoretical maximum of 16 million FC devices.  SANs of any degree of complexity should be therefore be based on a switched fabric using Fibre Channel switches with varying numbers of ports – typically 8, 16, 24 or 32 ports.   Switches with a large numbers of ports (typically 64 or above) are also available with additional fault-tolerant features and are known as “directors”.  Director-class switches are very expensive, but are the best solution for large scale SANs that will have a large number of host servers attached.  Switches can be cascaded and linked together, but the available port count can soon be diminished by the requirement for Inter-Switch Links (ISLs).  For a large SAN an ideal solution would be large directors at the centre of the fabric with smaller switches connected off the director via ISLs – the so-called “core-to-edge” solution [5].

Interoperability between elements of a SAN fabric needs careful investigation and it may be prudent to stick with just one vendor for the provision of switches.

Figure 2 A schematic illustrating how no single point of failure can be achieved through dual-pathing to each SAN component using separate fabrics ‘A’ and ‘B’.  Even more resilience may be achieved through the use of two nodes located in separate sites.  In reality, storage arrays and tape libraries would be connected with more than just one fibre connection to each switch.
To maximise the benefits of a SAN, ideally dual redundant fabrics should be used, meaning that each server has two HBAs, each attached to different Fibre Channel switches that then have separate connectivity to the storage arrays.  With suitable additional software installed, such a dual-hosted environment can also be used to provide dual-pathing with automated path failover or even path load balancing (see Figure 2).  Figure 2 also shows how an even greater level of resilience can be achieved by replicating the SAN infrastructure over two separate sites.

Some SANs require additional specific software on the hosts connected to the SAN beyond the HBA driver itself.  This may be needed to provide the resilience and management of the SAN and may be required even when only one HBA is installed in a host server.  On some SAN systems this software can be expensive and an unexpected additional cost of purchasing an HBA.

In the switches a technique called zoning is used to partition access between devices that are allowed to communicate with each other.  Zoning might also be used to create barriers between different operating systems environments e.g. between UNIX and PC systems or between corporate business systems and student teaching systems.  Further control of access between SAN components is possible by LUN masking, usually implemented in the storage arrays (see below).


Fibre channel fabrics now generally run at 2Gbps, with 1Gbps ports also still available.  Most 2Gbps products can switch to 1Gbps, thereby still preserving investments in the slower technology.  A 2Gbps link translates to 200MBps transfer rates and Fibre channel also can offer full-duplex mode.  However, some connection slots for the HBAs cannot sustain these throughput rates in full-duplex mode.  PCI 64-bit cards at 66Mhz or PCI-X slots (133Mhz) are the best choice to ensure high end-to-end transfer rates to fully utilise the potential of Fibre Channel.  Very recently, 4Gbps Fibre Channel has been announced, but many Fibre Channel proponents believe that 10Gbps should be the next leap in performance to match 10Gbit Ethernet.  However, 10Gbps Fibre Channel is not intended to be backwards compatible with previous slower standards.

In fact, whilst SANs have been mainly based on Fibre Channel technology, new IP based options using more commodity-like components (e.g. Ethernet switches) are a possibility in the future.  In particular, the standard for iSCSI (Internet SCSI) was agreed during 2003 and many products supporting iSCSI [6] are now appearing on the market.  Servers for iSCSI either require an iSCSI HBA (known also as a TCP Offload Engine) or a standard Ethernet Network Interface Card (NIC) with a special software iSCSI driver on the host server, with the former very much preferred.  Storage for iSCSI needs either a native iSCSI interface or (perversely) can be Fibre Channel storage with an iSCSI to Fibre Channel gateway device.

iSCSI as a replacement for Fibre Channel based SANs is not going to be realistic until 2005 and, whilst opinions vary on this topic, iSCSI may complement Fibre Channel, which might remain in the data centre to support enterprise systems.  However, 10Gbit Ethernet is already available and there is a more aggressive roadmap for future Ethernet standards than Fibre Channel.  These factors may reduce the theoretical advantages of a Fibre Channel fabric for the transport of storage data.
1.3                    Disk Technologies
Enterprise class storage arrays used in SANs generally use Fibre Channel interfaces to internal FC-AL connections in the storage array with FC disks attached.  More modestly priced storage arrays are available with an internal connection to either SCSI or ATA disks.  Fibre Channel disks are designed for enterprise-class use and usually have top-end performance and reliability characteristics and thus attract premium prices.

However, in recognition of the fact that not all data needs to be treated equally (see the section Data Categorisation Strategy below), many SAN vendors now offer the option of storage arrays based on Serial ATA (SATA) disk technology [7].  Serial ATA disks are an evolution of the commodity parallel ATA (or IDE) disks used in PCs with a design intention of being at ATA-like price-points with SCSI-like performance.  Such disks may not be suitable for mission critical enterprise database applications, but may have a role for less critical or low usage data.  Indeed, some storage vendors now offer storage arrays that can accommodate various varieties of disk in the same cabinet e.g. FC and SATA.  In such examples, the interface to the disk tray from the hosts/fabric is still Fibre Channel.

Low priced RAID arrays based on traditional ATA/IDE disks that can be incorporated into SANs have also been available for some while, but are now likely to be displaced by these Serial ATA arrays for the lower end of the storage array market.  Another new technology for disk drives is Serial Attached SCSI (SAS) [8] that, like SATA, continues the trend away from parallel methods of data transmission to serial methods (with simplified cabling and more flexible connectivity).

The threat of widespread adoption of Serial ATA and Serial SCSI disks should also have a beneficial knock-on effect on the prices of top-end Fibre Channel disks.
1.4                    Storage Arrays
Storage Arrays present a view to the host servers called a Logical Unit (LUN) that appears to the host as a disk volume.  A LUN is in itself a level of virtualisation as it is usually associated with some degree of RAID level and thus formed from parts of several disks.  Storage arrays typically implement several levels of RAID, with levels 0, 1, 3 and 5 very prevalent, with other combined levels (such as 0+1) also possible.  

The degree of control over the placement and use of actual disks varies when defining a LUN – some storage arrays offer a full level of virtualisation where storage administrators merely request a LUN of a given size, which is then created internally within the array and spread over many disks as determined by the array’s in-built virtualisation.  In many other arrays, however, there is full control over the placement of LUNs across the actual disks in the array and the array may need its storage to be partitioned into separate “RAID Groups”, with a particular RAID level associated with the group.  In such cases, administrators must carefully bear in mind the potential needs for expansion when designing their LUN structure (and associated RAID types) to ensure extra disk space may be added and allocated to the LUN.  Otherwise, expansion may sometimes need to be achieved by defining a new, larger LUN and copying all the data across.

Storage arrays typically also include caches to improve read and write performance by acting as a buffer between the storage array and the server requesting the I/O operation.  It is particularly beneficial for RAID types that require writing to multiple physical disks.  However, events such as power failures or failure of the array’s storage processor do require very careful attention and techniques such as battery backup and writing of the cache to disk when these events occur should be used.

Storage controllers in the array control the data flows between the array’s Fibre Channel connecting ports and the actual disk modules constituting a LUN.  The storage controller will also monitor the basic “health” of the array and its disks.  An enterprise-quality storage array will also typically have more than one storage controller, providing extra resilience and sometimes extra performance as well.  If multiple controllers are sharing the I/O load, then there is an additional level of complexity of cache management to ensure coherency between the caches.

Storage arrays have varying numbers of external Fibre Channel interfaces to connect the disks to host servers via the fabric.  Although 2Gbps fabric equates to 200MBps transfer rates, the total aggregate sustainable throughput into and out of the storage array needs careful consideration for the workload patterns to be supported.  The number of internal loops inside the storage array and numbers of disks attached to these loops should also be considered when assessing the suitability of SANs for really I/O intensive work.

The distribution of paths from LUNs through the storage controller(s), external Fibre Channel interfaces and the fabric may need careful consideration if load balancing software is not being used in order to ensure even distribution of I/Os through the SAN.

Disks in a storage array are usually hot-pluggable so that service to users is not disrupted when disks are added or removed.  The ability to allocate some disk as hot spares is also usually supported.  Use of a hot spare means that in the event of a disk failure, the storage array will automatically begin to rebuild the failed drive’s data onto the hot spare disk, continuing service if suitable RAID levels are in use.  When the failed drive is then replaced, the storage array will usually rebuild onto the newly replaced disk, leaving the original hot spare available to handle any subsequent failure.

The Storage Arrays possess varying levels of “intelligence” that depends on the storage controller(s) within the array and on the software products installed in the controllers.  An example of such capability is LUN masking that is used to determine which host servers can have access to each LUN.  This prevents unauthorised access to data from other servers or from server operating systems (e.g. Windows Server versions prior to 2003) that search round for available storage on booting.  Although LUN masking is often implemented in the controller within the storage arrays, it is also often a feature of storage virtualisation software (see the Storage Virtualisation section below).

The storage array controllers will also typically be able to provide other enhanced facilities such as:
Snapshots – rapid point-in-time copy of a LUN with only changes recorded; may be attached to another server for analysis or to be backed up;  unchanged blocks refer back to the original source LUN
Clones – full point-in-time copy of a LUN that can be used as a true copy of production data; uses same amount of disk space as source LUN and may take time to produce the clone, depending on its size
Replication/Mirroring – the ability to replicate data to another storage array, either synchronously or asynchronously; may be used for DR purposes and particularly useful when the two storage arrays are at physically separate locations

Please note that vendor terminologies for the above may vary, and that these capabilities are usually provided by additional software options for the storage array’s controller and may well be additional cost items, sometimes attracting premium pricing.  Storage Virtualisation software if used (see the Storage Virtualisation section below) can also provide this enhanced functionality.

The enhanced facilities above are those that distinguish SAN solutions from Direct Attached Storage solutions and are the basis of the additional flexibility, improved resilience and enhanced disaster recovery capability that will underpin the business case for a SAN.  NAS devices can also incorporate some of these enhanced facilities such as snapshots, but are not generally designed for replication to other devices.

When using these enhanced features of storage arrays to fully exploit the potential of SANs, ensure that any limits, both inbuilt/technical and through licensing, are known in advance when configurations are being planned.  There may be limits on the number of snapshots allowed or number of LUNs that may be mirrored etc.
2.0                  Centralised Backup Systems
Ideally a SAN should be linked to a Centralised Backup System (CBS) to provide operational efficiencies in backup/restore operations and eliminate the plethora of disparate backup systems typically found in an HE or FE institution.

These different backup systems typically arise when PC and UNIX support staff pursue their own backup utilities or use those supplied by the operating system vendor.  Similarly, different schemes may be used to address differing business/academic requirements.

Current backup systems are diverse, complicated and not easy to manage. Most SANs will be purchased with an associated tape library capable of reading/writing to tape media in several tape drives with robotic control of a large number of tapes held in slots in the library.  Enterprise tape libraries will typically have features such as bar code readers to identify the tapes and be capable of exporting/importing tapes that need to be taken off site/brought back onsite to and from fireproof safes. Not all tape libraries have native Fibre Channel interfaces, so it may be necessary to attach them to the SAN via a Fibre Channel to SCSI bridge device.

Various types of tape media are available for use in tape libraries.  The DLT format has been the most popular for several years with the LTO/Ultrium format rapidly gaining ground.  In the future these two formats are expected to dominate with a roughly equal market share [9] and convincing roadmaps for development [10, 11].

Both these tape formats have already gone through stages of evolution with different generations of tapes and drives available with continually improving capacity and performance characteristics as new versions are introduced.  The latest generation of LTO (LTO 2), for example, has excellent throughput characteristics and a single server may not be capable of sustaining such a drive in its optimum streaming mode.  Backup products that allow the inter-leaving of backups from multiple sources can assist with more efficient utilisation of modern tape devices.  Sites should, however, consider the impact on restore times of highly inter-leaved backups.

A SAN based backup solution allows back up of data to be consolidated into one system architecture. With appropriate options purchased with the backup software product, backups may optionally be driven across the SAN thus reducing the bandwidth overhead on the campus network - the so called “LAN free” backup mode [12].  LAN free backups are attractive when network traffic levels on the LAN are an issue, but sites should note that LAN free options in backup products are usually additional cost items, often with a premium price attached.

A further refinement is the concept of server-free backups [12], where data transfer occurs directly between the storage array and the tape library, although server-free backup products are not yet mature and proven.

Enhanced facilities offered by the SAN (such as snapshots) can also be used to reduce the impact of backup activities on production systems.  A near-instantaneous snapshot may be taken and the newly created snapshot LUN then attached to the backup server to carry out the actual data backup, reducing the amount of time databases, for example, need to be offline or in hot backup mode.

Increasingly, with the availability of cheaper disks (e.g. SATA) in SAN storage configurations, backup vendors are also providing options for disk-to-disk backup.  In this scenario, data can be copied to disk in real-time over the SAN and then backed up to tape off-line, e.g. during the day. This greatly extends the ‘backup window’.

Deployment of a SAN would allow for consolidation (with matching cost saving) on backup infrastructure over its life-cycle along with increased productivity of systems and support personnel.
3.0                  Strategic Fit and Industry Positioning
The take up of NAS and SAN solutions is rising and a NAS or SAN solution is cheaper to run than DAS. Total cost of ownership in the generic business sector has been found to be 55-60% cheaper than an equivalent amount of DAS storage. The industry as a whole reports an average support cost reduction of 80% (based on FTEs per MB storage) compared with supporting the equivalent DAS infrastructure. Further cost savings are seen following backup consolidation (typically 50-75% in tape drive consolidation) [13].

The benefits of using SAN and NAS technologies to consolidate storage are compelling [14].  The Butler Group believes that storage consolidation should be a primary objective for an organisation looking to optimise its IT infrastructure [14].

Fibre Channel SANs and IP-attached NAS are now established technologies. The usability of management tools is rapidly improving as they provide greater automation and become available for more platforms. In most cases, the savings and improvements in staff productivity, utilization rates and data availability more than justify the additional cost of installing SANs.

The future will lead to more interoperability and the adoption of open standards throughout the industry. New developments will see ‘intelligence’ being combined with storage. For example, an application should be able to tell the storage system that it needs more storage and then be assigned that additional resource automatically.

Major operating systems vendors are also acknowledging the greater uptake of SAN technologies.  For example, Microsoft’s Windows Server 2003 operating system has new features to enable SAN support [15]:
Virtual Disk Service (VDS)
Volume Shadow Copy Service (VSS)
Multipath Input/Output (MPIO)
Internet SCSI (iSCSI) support
Ability to boot from a SAN
Controlled volume mounting at boot time

Storage vendors are producing “plug-ins” for the Windows Server 2003 features above e.g. for VDS, VSS and MPIO – this trend for more SAN awareness in operating systems will further aid the manageability of SANs.
4.0                  Data Growth Rates and Their Management
The explosive growth of the Internet, email (with attachments), integrated enterprise business suites and greater use of digital media in personal devices (e.g. cameras) is creating unprecedented demand to store, retrieve and communicate information.  In fact the world’s population is expected to create more information in the next three years than in all the years of prior existence! [9].

Generic demand for storage across all business areas is growing. Storage growth estimates show a 76% increase in demand for storage per year across all data types. Big growth areas include e-mail (100-300% growth per year), data warehousing (72-115% per year) and internet content (75%). Customer Relationship Management (CRM) systems are also requiring more storage (growth 47% per year) [13].

Demand for storage in the HE/FE sector is growing in line with other business sectors. Growth is predicted within the e-mail and internet content data types and also newer functionality such as data warehousing and digital media storage.

Storage may be becoming cheaper in terms of cost per megabyte, but high data growth rates and the cost of management and backup of all this data are becoming prohibitive.

Fundamentally over recent years, the cost of storage has decreased in terms of the capital cost per megabyte of storage.  However, the total lifetime cost of storage including its management, backup and maintenance should be considered.  Many different industry analysts quote prices per megabyte of storage and varying factors of that cost per megabyte to manage it.  A conservative estimate is a factor of three for costs of management of storage over its lifetime versus initial purchase costs.

Industry analysts also publish varying figures for the different costs of managing DAS, NAS and SAN storage.  However, the essential point is not the absolute value of any analyst’s figures for these architectures, but the experience borne out in reality is that many more gigabytes, even terabytes of storage can be maintained by a given amount of staff resource for a SAN compared to a DAS scenario.  These economies of scale are even more apparent when a Centralised Backup System (CBS) is an integral part of the SAN landscape.

Management of escalating amounts of storage is indeed one of the chief challenges facing IT support organisations in all sectors.
5.0                  Storage Management
Storage management can encompasses several layers: management of the individual devices constituting the SAN (SAN Management), management of them as a virtual resource pool (Storage Virtualisation) and management/reporting of the data characteristics and growth patterns (Storage Resource Management).
5.1                    SAN Management
SAN Management software is needed to actually configure and monitor the components of the SAN to enable them all to function together.  It is directly concerned with enabling and controlling the movement of data within the SAN infrastructure.

SAN Management products are typically able to:

Discover devices attached to the SAN – hosts, storage devices, switches and other fabric components
Manage and monitor ports on the Fibre Channel switches
Administer zoning on the switches to selectively enable access
Administer LUN masking in the storage arrays to partition access to particular servers
Monitor traffic levels and performance between components and through the switches
Manage configuration changes within the SAN
5.2                    Storage Virtualisation
Virtualisation is an overused term in computing and in the specific area of storage, there is also much scope for confusion over the use of the term “storage virtualisation”.  Some storage arrays, for example, have in-built virtualisation features whereby the location of data and the disposition of storage LUNs are hidden.

Storage Virtualisation for the purposes of this report is an additional (optional) layer of storage management that can provide a centrally managed pool of storage with virtual volumes being made available to servers, as illustrated schematically in Figure 3 below.  Such virtualisation solutions have the additional merit of operating in heterogeneous SAN environments, consolidating the storage devices from several vendors.

Such virtualisation solutions [16, 17] fall into two camps: (a) in-band or symmetric and (b) out-of-band or asymmetric solutions.  For in-band solutions all control functions, metadata and data pass through the storage virtualisation server or appliance.  For out-of-band solutions, only control data and metadata (data about the data) passes through the storage virtualisation server or appliance with raw data flows being direct between host servers and the storage arrays.  Unlike in-band products, out-of-band solutions require the installation of an agent on each host server to enable communication with the storage virtualisation server for volume information and control, but allowing direct communication with the storage virtual volume for actual read/write data transfer operations.  (Some in-band solutions may also require software on the host anyway.)

Storage Virtualisation products are typically able to:

Allocate virtual volumes of a given size with no knowledge needed of the underlying hardware architecture
Enable non-disruptive dynamic expansion of virtual volumes (subject to the host operating system being able to cope with this)
Operate in a heterogeneous environment with servers and storage devices from various vendors
Manage the multi-pathing between servers and storage devices
Manage the data mirroring capability (potentially across heterogeneous environments)
Support LAN-free (and sometimes Server-free) backup schemes
Support snapshots for more efficient backups or point-in-time restore capability
Implement LUN masking to partition access to particular servers
5.3                    Storage Resource Management
Storage Resource Management (SRM) is a higher (optional) layer of management that doesn’t control the flow of data within the SAN, but rather analyses and monitors the patterns of data access and usage, possibly including charge back features.  Some basic SAN management software is essential for the functioning and continued well-being of a SAN; SRM software is a desirable, but not essential component of a consolidated storage environment.

One of the key drivers for a SAN is the need to consolidate storage (and servers) and this task is considerably aided by knowledge of how existing storage is being utilised, the patterns of data access and how much data is changing etc.  For example, data may be replicated several times or old data stored without being deleted, both adding to the cost of storage without providing any added value to the organisation. SRM software can provide reporting features to better maintain existing storage and to more effectively plan future storage architectures.

SRM products are typically able to:

Provide an enterprise-wide inventory of storage (including storage outside of the SAN)
Identify unused files (not accessed for a long time or “orphans” with no current valid data owner)
Check that modified files are backed up
Monitor overall growth trends to enable future storage needs to be planned
Identify the specific types of data being stored and their storage growth trends
Provide utilisation reports by person, department, filesystem, server etc
Provide charge back mechanisms or reports that can be input into separate charge back systems
Provide web-browser interfaces and be portable to UNIX, Linux and Windows environments
Enable implementation of storage polices for different categories of data
Support heterogeneous platform and storage environments
5.4                    SMIS/Bluefin Storage Management Initiatives
SAN management tools have historically been very specific to each vendor’s storage components with poor interoperability across heterogeneous environments.  Storage vendors are now beginning to produce products that do operate with a wider variety of storage hardware.  Also, Storage Virtualisation products (see above) that can hide an underlying miscellany of diverse equipment types may in their own right also provide overall SAN management functions.

In recognition of poor interoperability potentially impeding the uptake of SANs, the Storage Networking Industry Association (SNIA) [18] has sponsored standards for multi-vendor interoperability.  One such standard is the Storage Management Initiative Specification (SMIS) [19] that was also formerly known as “Bluefin”.  SMIS-compliant products are evolving but by 2005 are only expected to offer rudimentary SAN management functions such as device discovery, configuration and error management.  More sophisticated functionality such as snapshot management is not expected before 2006-7 in SMIS-compliant products.  Consequently, inclusion of standards-based support cannot yet be a decisive factor in choosing a SAN supplier.
6.0                  Data Categorisation Strategy
Not all information needs to be treated the same as the value and importance of information varies.  Information needs to be categorised into different levels of criticality that determine the appropriate means of handling the data throughout its lifetime.  As the usefulness of data varies over time, there is a need to consider Information Lifecycle Management (ILM) so that data may be stored on different types of media as it ages and becomes less business critical.  For example data may initially reside on enterprise-class Fibre Channel disks in a storage array and then be later migrated to cheaper Serial ATA disks or to nearline tape storage.  Eventually, after a further period of time, the data might finally only reside on offline tape storage.

In normal circumstances each category would have appropriate availability expectations, supported by differing infrastructure architectures e.g. use of clustering or mirrored data on the SAN etc.

In the case of an incident, the time to recover and the point to which recovery must be made need to be considered for each category of data [20].  These are the Recovery Time Objectives (RTO) and Recovery Point Objectives (RPO), respectively.  The RTO is the target time taken to recover a system and the RPO is the target period in time to which data must be recovered (dependent on how much data/transaction loss can be tolerated).

Varying levels of criticality are used, with typical definitions being similar to the following:

High criticality information is that which is essential for the organisation to operate effectively and where the absence of it, or inaccuracy in it, at a time it is required, would have catastrophic results on the functioning of the organisation or its reputation

Medium criticality information is that which would take considerable effort to recreate if it became unavailable for a prolonged period of time, or corrupted, and which would cause significant disruption to the functioning of the organisation through its absence or inaccuracy.

Low criticality information is that which can be recreated easily and the unavailability or inaccuracy of it would be nothing more than inconvenient to the organisation.

Some sites may also have another category:

Mission critical/continuously available information is that which must be available continuously where no downtime can be tolerated and examples would be online e-commerce sites, air traffic control or critical health care systems.

Typical normal availability expectations and recovery objectives in the case of incidents might be:


Normal Availability
RTO
RPO
Mission critical
100%
0
0
High criticality
99.99%
0-12 hours
Minutes
Medium criticality
99%
12-72 hours
Hours (up to 24 hours)
Low criticality
95%
> 72 hours
Days (1-7)
7.0                  Fit of a SAN into a Data Categorisation and DR Strategy
A SAN can support an institutional data storage strategy whereby data of a high criticality is mirrored and duplicated on the SAN (providing high availability and resilience). Medium criticality data may also be stored on the SAN but might not be mirrored in real-time, or an asynchronous mirror might be used or no mirroring at all. Low criticality data could be stored on the SAN or elsewhere, with no mirroring or duplication. All data types would be backed up, however, using the associated centralised backup system tape library (or libraries) attached to the SAN.

The SAN permits rapid server recovery in the event of a server hardware failure – replacement servers can be simply “pointed” to the appropriate disks on the SAN. There is no need to move data to the new hardware. This downtime could potentially be reduced to minutes. Multiple copies of data can be held on the SAN through technology known as “snapshot” capability. Snapshots of mission critical data can be taken at various times during the day without impacting the user. In the event of a corruption, this snapshot can then be presented to the host system in minutes. In addition, the increased fault-tolerance of a SAN would mean fewer out-of-hours data manipulations, therefore generating a saving in staff overtime.

Many organisations are moving towards greater use of server clustering to achieve higher availability and better recovery ability.  In a clustered environment, the failure of any one server would not cause a service to be unavailable as other servers in the cluster would take over the work load.  Clusters operating over a distance (often known as “stretched clusters”) also provide disaster recovery capability if the workloads can be switched to the other, still-functioning site in the event of total failure of a data centre, for example.

SANs with their shared storage naturally lend themselves to supporting server clustering.  A combination of clustered servers accessing data on the SAN with its inherent reliability features provides a means of ensuring high availability.  If sites have multiple machine rooms then separate storage nodes could be located sufficiently apart and data mirrored such that loss of one data centre would not impact the availability of high criticality data. Deploying a SAN across two nodes in two separate locations would provide for much improved disaster recovery capability, as illustrated by Figure 2.
8.0                  E-Science/Grid Support
The national e-Science Grid Programme [21] and other Grid initiatives are aiming to develop distributed high-performance computational facilities for researchers to be further complemented by additional data intensive facilities.  This combination of compute intensive and large capacity data storage is the basis for a “research infrastructure”.

SANs with their inherent reliability features and ease of scalability can naturally support this required data intensive infrastructure. Specialist servers/high-end workstations might be directly attached to the SAN to support these e-Science and other research initiatives.

This research infrastructure could be enhanced by possible extras such as Hierarchical Storage Management (HSM) system or other archiving facilities that may not necessarily be included with any initial SAN configuration.  Research data is typically characterised by large volume and often relative inactivity once analysed.  It needs to be archived in the longer term as, typically, further analysis is run later as better systems and means of analysis develop.

9.0                  Benefits of a SAN
9.1                    Reduced hardware capital costs
Centralised storage means that new hardware procurement for centrally managed systems will require little or no local disk provision. For major corporate systems and large server environments, this affords a significant cost saving.

Furthermore, in those HE/FE establishments with large numbers of servers run by local departmental IT support personnel (outside of the central IT service) , substantial further cost savings would be made through server consolidation (reducing the total number of servers needed) across the entire HE/FE establishment. This could be achieved by removing the need for departments to host, operate and manage their own servers for file or email provision, for example.

 An additional cost saving would be afforded by being able to redeploy some staff effort currently assigned to managing these departmental servers.

A SAN would permit central IT providers to offer “managed storage” to users across the campus. Disk space could be made available on the SAN through central high-availability clustered servers. This would maximise the “economies of scale” benefit of deploying a SAN.

Surveys indicate that 50% of storage is typically unused in organisations (commercial and public sector) so that savings can be made by not purchasing this unnecessary storage across the institution as a whole.

9.2                    Reduced effort to manage storage
The centralised, consolidated storage environment provided by a SAN (and particularly with an associated CBS) provides for easier management of data compared to a DAS environment.  From figures given in the Merrill Lynch [13] or Butler [14] reports, nearly half the total lifetime cost of a DAS environment is the people cost, whilst for NAS and SAN environments people costs are only about an eighth of the lifetime costs of ownership.

This enhanced efficiency of management for networked storage environments (SAN and NAS) results in a greater volume of data being capable of management by a given individual.  Industry surveys suggest that the “Terabytes per FTE” are between 3 and 4 times greater for networked storage compared to DAS.

9.3                    Increased productivity through improved fault tolerance and DR capability
The enhanced disaster recovery capability of a SAN would lead to increased availability giving the potential for significant staff (and student) productivity savings.  It is very difficult to cost accurately the effect of server or system downtime; therefore some sites may not be able to include downtime reduction as a tangible benefit in their cost/benefit analysis.  However, it should then be highlighted as a major intangible benefit in the business case if actual costs savings cannot be accurately determined.
9.4                    24x7 Availability
A SAN can provide 24x7 availability as there should be no single point of failure within a suitable designed SAN infrastructure.

Most HE/FE institutions need to accept a trend to widen their provision beyond the needs of the classic 18 to 21 year olds who enter higher education after A-levels (or after a gap year).  National pressures for widened participation (from non-traditional student backgrounds), increased student numbers and distance learning all dictate a need for facilities to be available during non-standard parts of the day.

Traditional students also now have higher expectations for an “enhanced student experience” (partially through fees being payable), reflecting trends in society as a whole for greater expectations from “infrastructure” reliability.

This all leads to the need for increased availability of teaching services so that from the student point of view teaching and learning facilities are always available (i.e. 24x7).

9.5                    More efficient backup
As the tape library in a typical Centralised Backup System may be used to backup data from several different servers, the speed of backups may be improved.  This is a result of data potentially being inter-leaved on the tape from several sources, sustaining the tape drive at its maximum streaming operating efficiency.  The utilisation of tapes may also be improved by this sharing of tapes from many sources, leading to reduced numbers of tapes being needed and also fewer tape drives to backup a given amount of data.

A large tape library will essentially operate in unattended mode with the minimum of human intervention.  A sufficiently large tape library will enable cycles of backup tapes to be kept in the library for longer periods e.g. a full week or even a month or longer, avoiding the need to physically fetch tapes from the fireproof safes for restores.  Clone copies of tapes for safe keeping in fireproof safes should still be made, so some operational effort to remove tapes from the library for storage in a fireproof safe will still be needed.  However, considerable operational efficiencies will be achieved and the CBS element alone of any SAN Business Case should produce substantial savings by rationalisation of backup/restore activities.

9.6                    Scalable Storage
A SAN allows for “pay as you grow” storage scalability, pro-active storage planning and non-disruptive growth/reconfiguration. Extra disks can be purchased at any time and added to the total storage provision. Configuration utilities allow for that storage to be ‘presented’ to any host that requires space. Free space can also be re-assigned as necessary. Typical sites find that up to half their disk space is unused (not allocated) and in hardware terms alone (i.e. not including maintenance and administration) substantial savings in purchase costs could be made.

9.7                    Interoperability between diverse systems
Disparate computer platforms can share the SAN as their common mass storage system. The SAN would then provide a totally heterogeneous environment, enabling cross platform functionality (e.g. between UNIX, PC and other operating systems) for activities such as file and print serving, database hosting, high-performance computing needs etc. In fact, new developments allow systems to boot direct from a SAN; servers would then require no local storage whatsoever.  This could then possibly allow “spare” servers to be kept that are able to be allocated to any of several operating systems in the event of a server failure.

9.8                    Centralised Management
Centralised management will afford staff productivity gains as well as reduced total cost of ownership through intelligent storage management (only one storage dedicated team performing the work of many systems administrators), economies of scale (purchasing terabytes of disk space in one go rather than lots of small disk sub-systems), cheaper hardware (servers no longer need specifying with individual disks and expensive RAID controllers), centralised (and shared) backup and restore architecture. Centralised management will also facilitate common standards in storage management according to an institutional storage policy (e.g. standards in disk allocation, levels of fault-tolerance, scalability, utilisation and back up/recovery mechanisms across the institution). This should also assist sites with disaster recovery and security audits.

10.0               Justification for SANs – Writing the Business Case
Investing in a SAN infrastructure is a major undertaking and whilst it is beyond the remit of this report to quote prices, it is certainly easy to incur expenditure in the region of between say £200k and £1M for an “institutional SAN”.  Consequently, purchase of a large scale SAN (and associated Centralised Backup System) should be regarded as an institutional strategic decision with any Business Case containing many references to aims and objectives set out in the organisation’s institutional strategy documents.

Typical institutional strategic aims that might be referenced are in areas such as the following:

Electronic storage of data and processes and procedures to ensure data backup and recovery (may be part of an institutional data storage strategy)
Adherence to institution-wide standards
Use of common integrated systems
Central generic provision versus devolved local provision
Support of lifetime learning, distance learning and widened participation
Support of any time, any place, 24x7 access

The benefits of a SAN outlined in the above section should be linked to these institutional objectives to underpin a more robust information infrastructure for the institution.

The SAN Business Case therefore requires the support of senior business managers in the HE/FE institution and should not be seen as the latest technological development that interests just the central IT provider in the institution.

Initial purchase costs and ongoing maintenance costs are typically large and any benefits and return on the investment may be treated with scepticism initially in some quarters.  However, the production of a properly costed business case showing the total costs and benefits [22, 23 and 24] over the extended lifetime (e.g. 5 years) of this equipment should show net benefits well within that period.

Factors to include in any cost/benefit analysis are:

Reduction in numbers of servers
Reduction in backup infrastructure complexity
Staff productivity gains for backup administration
Savings by not having large amounts of unallocated disk over the campus
Reduction in systems and support staff out of hours working
Reduced costs of server upgrades – little or no local disk required
Possibility of offering centrally managed “commodity” storage leading to staff efficiency gains elsewhere on campus in a devolved environment
Improved productivity by reduced downtime
11.0               Risks/Issues
The above two sections of this report have presented the positive aspects of the potential of a SAN (as needed to make the business case).  However, procurement, installation and configuration of SANs in 2003 is still a highly complex and lengthy exercise with many unexpected interoperability problems.

The following risks/issues include some of the negative aspects of using SAN technology that sites must be fully aware of and these are based on the negative or unexpected experiences of HE/FE sites that have already procured and installed SANs!  Some of these risks should also be included in the Business Case so that senior managers in the HE/FE institution have adequate information on which to base their decision on the merits of SANs (or not).

a)       For a SAN to encompass a substantial proportion of the data storage needs of an HE/FE institution there needs to be a cultural change in the way storage is considered – data to be considered by type and criticality according to an institutional storage strategy, with fewer individuals having control over their own disk storage.  A SAN is easier to “sell” if departments with their own server/storage solutions are prepared to accept more centrally delivered storage.  Political considerations may require as much time as technical and financial issues.

b)       An inadequately resourced or poorly designed SAN can itself be a single point of failure for a large volume of data.  On the other hand, a properly resourced and well designed SAN can eliminate single points of failure and provide enhanced resilience, but this does require a high level of investment to achieve (e.g. with dual fabrics, dual HBAs, mirroring etc).

c)       A properly resourced and well designed SAN also needs to take into account aggregate throughput needs of all the many servers attached, so as not to become a performance bottleneck.

d)       SANs are relatively complicated to implement and require significant training needs for both server/storage support teams and operations support staff that carry out backups and monitoring etc.

e)       Sites not having appropriate staff to run a SAN may wish to consider NAS as a solution to server/storage consolidation needs, particularly if the serving of file systems caters for a large proportion of storage needs.  Buying many different smaller NAS devices should be avoided, however, as the advantages of storage consolidation and staffing efficiency gains will be lost with equipment from many different vendors.  Alternatively, a managed SAN service provided by a storage provider or leasing of storage and/or services could be considered.

f)        DAS still has a role as the cost of HBAs, dual pathing and requisite software for SAN environments can add a premium to the costs of connecting a server, making it unrealistic for small or completely self-contained functions.

g)       Despite vendor marketing ploys, even now there are many interoperability issues between the various components of a SAN.  It is recommended that institutions wishing to procure a SAN probe vendors carefully about such issues during tender negotiations.  An example is HBA, switch, storage array, host operating system and patch level compatibility.

h)       Pre-sales staff appear to be genuinely unaware of some of the unexpected limits or compatibility issues that arise when SAN implementations begin in earnest.

i)         Similarly, pre-sales staff are not always aware of all software requirements for clients of a SAN, leading potentially to unexpected additional expense.  This confusion can still remain after installation has begun!  Software requirements for HBAs seem a particular area for confusion with many vendors.

j)        Incompatibility issues mean that vendors often want very exact details of operating system levels and patch levels of host servers together with firmware levels of HBAs, switches and storage controllers, and need to be informed of any configuration changes in order to ensure that they will offer support contracts.  This requires more disciplined management of the SAN compared to what HE/FE sites have traditionally been used to.  This leads to an additional level of formality of the interface with the supplier’s maintenance division.

k)       As a result of the above, some sites set up dedicated “Storage Teams” within their IT support organisations, whilst others handle the new workloads amongst existing server support teams.  This issue needs to be considered at each site with possible structural and process changes introduced [25].

l)         Many features that truly exploit the potential of a SAN (such as LAN-free backups, the ability to take snapshots or be able to do remote mirroring etc) will be extra cost items and vendors should be probed carefully to ascertain what is included in the base cost of a SAN.  Licences based on total size of storage or with bandings related to storage size should be studied carefully, particularly when future growth is considered.  Similarly, check that licences don’t have restrictions on numbers of hosts to be attached; again bearing in mind future growth in numbers of SAN attached servers.

m)     The whole question of whether to use some storage virtualisation product as another layer between the host servers and the storage will require much thought and debate.  Storage virtualisation products support heterogeneous environments and so prevent lock-in with any given storage vendor and even allow existing storage to be used.  On the other hand, it does mean effectively a lock-in with the storage virtualisation vendor to achieve this freedom to choose hardware at will!  If virtualisation is chosen, there is also the in-band versus out-of-band debate to be had as well.

12.0               Glossary

Abbreviation	Term	Explanation
DAS	Direct Attached Storage	Storage locally attached to a particular server.
SAN	Storage Area Network	A dedicated network of shared storage devices.
NAS	Network Attached Storage	Storage available from a device resident on the LAN and shared via file protocols such as NFS or CIFS.
LUN	Logical Unit (or Logical Unit Number)	A logical presentation of disk space created from individual disks, groups of disks or parts of multiple disks as defined by a RAID controller.
FC	Fibre Channel	A high speed, serial data interface allowing communication between servers, data storage devices and other communications devices such as switches.
	Switch	A device to connect hosts and storage devices, capable of supporting multiple dedicated non-shared data paths between devices.
	Zoning	A technique to partition FC fabrics to prevent unrestricted access between hosts and devices.
	LUN Masking	A technique to associate particular LUNs with particular host servers.
	Fabric	The switches and connection infrastructure providing the “network” paths between hosts and storage devices.
ISL	Inter-Switch Link	A link between FC ports on a switch where one switch is cascaded off the other.
iSCSI	Internet SCSI	A standard to enable block data transfers over IP networks by wrapping SCSI sequences into TCP/IP packets.
HBA	Host Bus Adapter	Used with Fibre Channel to take blocks of data and segment them into FC frames for transmission over the FC fabric.
GBIC	Gigabit Interface Converter	Converts optical signals into electrical signals and used to attach the SAN’s fibre connections.
SCSI	Small Computer Systems Interface	An evolving standard with many variations – first developed in 1986 – for transmission of data between hosts and devices (usually disks).
ATA	Advanced Technology Adapter	A type of commodity disk commonly used in PC systems.
IDE	Integrated Drive Electronics	Another term for commodity disks used mainly in PC systems.
SATA	Serial ATA	Serial (rather than parallel) version of ATA technology.
SAS	Serial Attached SCSI	Serial (rather than parallel) version of SCSI technology.
PCI	Peripheral Component Interconnect	An internal computer bus to attach devices; exists in several variations with different throughput characteristics.
TOE	TCP/IP Offload Engine	Used with iSCSI to take blocks of data and segment them suitable for transmission as IP packets over the IP network.
	Snapshot	A rapid point-in-time copy of a LUN where only changed blocks are tracked with unchanged blocks still being referred to in the original source LUN.
	Clone	A complete point-in-time copy of a LUN.
LAN	Local Area Network	That part of the network over which data normally travels between client machines and servers or between servers and other devices.
CBS	Centralised Backup System	Using large centralised tape libraries to combine the backups from several hosts.
CIFS	Common Internet File System	File system available to client machines over the network from a server machine; based on Microsoft’s earlier Server Message Block (SMB) system and popular in Windows environments.
RAID	Redundant Array of Independent Disks	Technique to improve the reliability and performance of disks by aggregating several disks and providing the appearance of one large disk to host servers.
NFS	Network File System	File system available to client machines over the network from a server machine; developed by Sun Microsystems and popular in UNIX environments.
HSM	Hierarchical Storage Management	A storage system whereby data may reside on different devices, ranging from fast-access media (e.g. disk) to slower media (e.g. tape) with a hierarchy of such storage devices available.
ILM	Information Lifecycle Management	Recognising that not all data needs to be treated the same throughout its life.
RPO	Recovery Point Objective	The point in time to which data must be recovered after an incident, reflecting the amount of tolerable data or transaction loss.
RTO	Recovery Time Objective	The amount of time taken to recover a system after an incident, reflecting how long it is tolerable for a system to be out of service.
SRM	Storage Resource Management	Software to analyse and monitor patterns of data access and usage.
SNIA	Storage Network Industry association	A not-for-profit trade association with a remit to ensure “that storage networks become complete and trusted solutions across the IT community".
SMIS	Storage Management Initiative Specification	An initiative by SNIA to “to develop and standardize interoperable storage management technologies and aggressively promote them to the storage, networking and end user communities”.
	Bluefin	An older name for what how now become SMIS.
	Virtualisation	An over-used term to indicate any apparent provision of an entity that does not physically exist, but is made to appear so by software or other simulation.
DLT	Digital Linear Tape	A very widely available tape technology that has been around for several years with continually evolving improved versions.
LTO	Linear Tape-Open	A tape format originally developed jointly by IBM, HP and Seagate and also referred to as Ultrium.
	LAN-free	A backup technique where data does not travel over any part of the LAN, but is self-contained totally within the SAN infrastructure.
	Server-free	A backup technique where data does not get handled by any servers, but travels directly from disk to tape storage under the control of some kind of data mover.