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  1. 1. COMP3013 CONFERENCE COMPUTING WHAT’S THE GENERAL PACKET RADIO SERVICE? Author name: Shilain Keshani 59 Brook Drive Harrow ABSTRACT The General Packet Radio Service1 has schemes and higher channel bandwidth that provided a massive increase to mobile data supports content impossible for regular usage and usefulness. A key issue here is mobile phone service. GPRS’s data how the technical and commercial features switching technique has offered a twist in have, or have not affected the widespread the way in which similar technologies have use of the service. The paper will aim to provided a means of communication. It identify the key issues in the GPRS provides a packet switch solution differing it technology, such as the user features; from preceded means that offer a similar network features, applications such as still service such as GSM which uses a circuit images, web browsing and document and switch transmission. GPRS is also called audio sharing. It will distinguish the benefits 2.5G, standing for 2.5 generation mobile and limitations of the service as well as it’s communication. It is often referred to as this effect on the market as a whole i.e. on the because it is an in between technology in customers, vendors, mobile channels, the sense that it is a more advanced 2 application developers and network generation technology, but not referred to as operators. Comparisons to other mobile 3G because it still has roots in the second telecommunication services will also be generation digital cellular telephony (2G). reported including the differences between Technologies such as GPRS are indeed a GPRS and the technologies that preceded step in the right direction to boost it. Discussions of this technology will be development of mobile data usage and throughout and the method of derivation usefulness. Under normal conditions, a from Global System for Mobile GPRS phone is able to deliver similar data communication will also be presented. throughput as a regular modem connected at 56Kbps enabling users to access the Keywords internet, mobile commerce, e-mail, General Packet Radio Service (GPRS), download audio and video, personalised GSM, Mobile Telecommunications, GPRS information delivery etc. The following applications. analogy has often been conveyed to explain the GPRS technology and what it is all 1. INTRODUCTION about: “GPRS is to mobile networks what One thing that GPRS has not got is any ADSL (Asymmetric Digital Subscriber Line) relation to the similar acronym GPS (Global is to fixed telephone networks- the favoured Positioning System). It is often described as solution for providing fast and inexpensive a giant step in the direction of the evolution internet links” [1]. GPRS is a provider of a of wireless technologies and this description direct link into the Internet from a GPRS has been forwarded due to the compatible mobile telecommunications differentiation of GPRS to current device. Pre-GPRS, things were much more technologies. It is derived from the GSM complicated and long winded. The market held an open niche for a new technology Permission to make digital or hard copies of all or part that increased speed and efficiency and of this work for personal or classroom use is granted GPRS was the proposed solution. Before, without fee provided that copies are not made or distributed for profit or commercial advantage and that in order to browse web pages, or transfer copies bear this notice and the full citation on the first files, the necessary steps were as follows: a page. To copy otherwise, to republish, to post on data call must be made, then this call is servers or to redistribute to lists, requires prior specific answered by a modem or and ISDN adapter permission. 4th Annual Multimedia Systems, Electronics and owned by either the network operator itself, Computer Science, University of Southampton such as T-Mobile or © 2003 Electronics and Computer Science, University of Southampton platform but with more efficient data 1 GPRS 2 GSM
  2. 2. Figure 3. GPRS System [2] exchanged. The user generally, is billed for the entire duration of the connection event an Internet Service Provider3. In the next in idle periods thus for e-mail and Internet stage, the caller will have to be surfing the method would be inefficient as authenticated by giving a user id and inevitably there will be gaps in the password and then assigned and Internet interaction between caller and destination. address by the ISP or operator. The process lasts a minute, too long for the 2.2 GPRS packet switched data eager Internet surfer, or the busy business GPRS involves overlaying a packet based professional urgently needing to view their air interface on the existing circuit switched e-mail when mobile. Adding to this, the packets and then transmitted and functionality of GPRS Software decreases reassembled at the receiving end. The the incremental cost to provide data method can be explained clearer as follows: services and allowing improved quality of A large picture gets ripped up and then put data services as measured in terms of into a small box. It is transported and while reliability, response time and features in transit may jumble up and mix. The supported. The aim of this Technical receiving end then opens the box, pieces up Briefing is to give technical information on the photo fragments to fit the relevant part the relevant topic and will not purely be and receives the message. Note: packets based on opinions, social issues, (torn up bits of picture), may take different comparisons or experiences. It will simply routes to their destination. The Internet is be a paper that provides factual information the most well known example of a packet on the topic that is GPRS. Its desired data network. To gain a better audience are not specifically trained understanding of GPRS, Figure 3 will be technicians or those who have no technical explained in detail. The figure begins with a knowledge whatsoever. The paper will be laptop computer and traverses through the constructive in providing useful and valid network. The laptop is connected to a technical information to those wanting to GPRS compatible mobile phone either by gain a deeper insight into mobile serial cable, Universal Serial Bus or wireless telecommunications, in particular GPRS. link. The mobile phone communicates with GSM base stations and the GPRS packets 2. GPRS NETWORK FEATURES are sent from the base station to what is called a Serving GPRS Support Node 2.1 The preceded circuit switched (SGSN). This node sends data to and from data the mobile stations. This node also keeps The circuit switched data method is said to track of the mobiles within its service area. be a less useful form of communication of The SGSN communicates with the Gateway data. The circuit switch method dedicates a GPRS Support Node (GGSN) which is a communication channel and sets it up system that maintains connections with between the calling and destination party. other networks such as the Internet. When This method is most practical for voice the mobile station sends a packet of data, it communication as an open wave of does so through the SGSN to the GGSN. interaction is established and a continuous This route converts them from transmission connection is devised. A key issue as to over the desired network which in figure 3 is why the circuit switch technique is shown as being the Internet. IP packets impractical for data communication is simply from the internet addressed for the mobile cost efficiency. Circuit switch data requires station are received by the GGSN, then a dedicated radio channel, even during quiet forwarded to the SGSN and then finally periods when no sort of interaction is being forwarded to the mobile station. 3
  3. 3. connection, once a GPRS mobile station 3. USER FEATURES OF GPRS registers with the network, it is ready to send and receive information. E-mail could be 3.1 Speed and immediacy sent directly to one’s laptop computer when Theoretically, the maximum data rate for not even connected. The user can does not GPRS is 171.2kbps. It competes for the even have to read the e-mail immediately, same network resources as voice and alternatively they can view and reply at a therefore has bandwidth limitations leading later time. The user in fact had a connection to a lower initial data rate of approximately for the duration and did not once have to 30kbps. The speed of GPRS is said to be dial in. GPRS will additionally allow for three times as fast as the data transmission simultaneous voice and data speeds possible over fixed communication, this means that the user is telecommunications networks and is an able to receive or make calls during a data increase on current circuit switched data session. The applications along with services on GSM by tenfold. The additional features of the technology will be technology works by amalgamating a discussed section 2.4. number of separate data channels. The data is broken down into small data packets, 3.2 Spectrum Efficiency and then these packets are re-assembled by Radio resources are only used when the the receiving handset back into their original users are actually sending or receiving data format. GPRS uses the same radio channel transmissions, this is mainly due to the as voice calls, a channel that is divided into method of packet switching. Available radio 8 separate data streams, each carrying resources can concurrently be shared about 34kbps. After the overhead between multiple users. This effective of Protocol and error correction, 14kbps is handling of scarce radio resources leads to left for data throughput. As GPRS can large numbers of users sharing the same combine up to eight of these channels if the bandwidth while being served from a single mobile device has no immediate limitations cell. This demonstrates that the spectrum data rates, the connection speed as efficiency of GPRS is high thus there mentioned reaches above 100kpbs. It is creates less need to build an idle capacity important to note that the number of that will only be used and functioned in peak receiving channels do not mach the number hours. It is for these reasons that GPRS of sending channels. Depending on the lets network operators maximise the use of environmental radio conditions, one of the their network resources in a truly flexible following four coding schemes can be way. This section summarised would be as selected and they are also shown in figure follows: GPRS improves the peak time 1: CS1, CS2, CS3, CS4. The first two capacity of a network since it simultaneously coding techniques offer good error detection assigns scarce radio resources more but with a low connection speed, and the efficiently by supporting virtual connectivity last two offer the opposite: faster connection and also immigrates traffic that was sent speed but little or no error correction using Circuit Switched Data into GPRS capabilities. Although the theoretical instead. It also reduces signalling channel maximum data transmission rate is based at loading by migrating traffic that previously a speed of 172.2kbps, this fact is assumed if was sent using Short Message Service to a single user is taking up all eight available GPRS. timeslots with no error protection. It is in Figure 1. Data rates for GPRS software [2] USER DATA CS1 CS2 CS3 CS4 RATE 1 TIMESLOT 9.05 KBPS 13.4 KBPS 15.6 KBPS 21.4 KBPS 8 TIMESLOT 72.4 KBPS 107.2 KBPS 124.8 KBPS 171.2 KBPS this scenario where users may not benefit from the speed of GPRS’s service as initially 3.3 The GPRS technical facts anticipated. As with a Local Area Network Figure 2, technical facts
  4. 4. Channel coding Outer blocking code, inner convolutional coding, interleaving scheme for error bursts Modulation Gaussian Minimum Shift Keying GMSK Multiple access Combination of TDMA & FDMA Transmit frequency bands Uplink reverse ch. 890-915 MHz Downlink forward ch. 935-960 MHz Duplex seperation 45 MHz RF carrier spacing 200 kHz Total no. of RF Duplex channels 124 No. of TDMA slots on each carrier 8 Channel allocation 1 to 8 time slots per TDMA One time slot (physical channel) 0.577 ms Frame Interval: 4.165 ms Asymmetric data traffic Different time slots for Uplink and Downlink Frequency hopping 217 hops/s (slow) Equalizer 16 us time dispersion Connectivity Packet switched data networks such as IP an X.25 Extra nodes Gateway GPRS support node (GGSN) Serving GPRS support node (SGSN) 3.4 Applications of GPRS As there is almost no time delay before sending data, users would gain great utility out of the application to extended communication sessions, e-mail, database queries, dispatch, card purchases, stock updates, news and sport information, roadside assistance etc. It has removed many obstacles that stood when users wished to use multimedia or view graphical web based applications. The technology would allow the users to participate in existing Internet chat rooms rather than setting up one’s own for mobile users. However the technology cannot support point to multipoint services and this will eradicate the ability of distribution of a single message to group of people. Even though the use of this technology is still useful in the above sense, it is clear that even today the Short Message Service has proved to remain the most used provider of chat applications. The GPRS mobile applications contain several characteristics that really enhance the usefulness and value to the users. The first of these is mobility, this means that there can be a
  5. 5. constant voice and communication standard networking protocols. The connection while running for the bus, driving following hardware platforms all take to an important meeting across the country advantage of the GPRS technology: etc. There is no obstacle in regards to location and there is no lengthy login • Laptops or handheld computers session and this makes the second connected to GPRS-capable mobile characteristic immediacy. The following are phones or external modems; general applications that can be applied by the consumer: • Laptops or handheld computers- capable PC Card modems; • Communications- email, fax, unified messaging, internet/intranet access; • Smart phones that have full screen capability, all phones these days are • Value Added Services- information colour and have this capability; services such as news, games; • Mobile phones able to use the Wireless • E-commerce- retail, ticket purchasing, Application Protocol, most modern banking, financial trading; mobile phone devices have this functionality; • Location based applications- navigation, traffic conditions, bus/airline/rail • Dedicated equipment with integrated timetables, location finder; GPRS capability, e.g. mobile credit-card swipers. • Advertising- products and services promotion; 4.1 Affiliation with Bluetooth technology • Vertical applications- freight delivery; Bluetooth is a short-range communications fleet management; sales force standard enabling wireless data automation. communications at ranges of about 10 meters. Typical applications of Bluetooth GPRS’s synergy with the Internet has technology include mobile phone hands free proved it to be not only a stepping-stone in kits. The handset can be placed in the technology but also a way of increasing user’s briefcase and calls can be answered one’s enjoyment and efficiency of carrying through an earpiece; documents can be out specific tasks. Any service that is used printed from a Bluetooth handset if it is over the fixed Internet at present such as within ten metres of a Bluetooth printer etc. the File Transfer Protocol, web browsing, Because each GPRS handset uses a chat and email is available over the mobile different menu structure it is not simple to network because of GPRS. As mentioned set up. There are many stages the user has before, it is the Short Message Service that to endure in order to set up the handset e.g. has remained the main bearer of locate and input technically unfriendly quantitative information, but the use of information with strange names like APN, GPRS has resulted in users being exposed CID and QoS. Also, the enablement of to other features (above) and given more roaming with GPRS is limited as parameters qualitative features such as those may need to be changed for each country mentioned. Images such as photographs, and network. A key problem with setting a pictures and maps can also be sent via the handset up is the limited screen display and GPRS technology. It is possible with GPRS keypad. With a Bluetooth link to a PC or to post images from a digital camera PDA one can use the more complex user connected to a GPRS radio device directly interface and screen display to guide them to a web site, this in turn allows near real through the process. Nick Hunn [6] “If time desktop publishing. GPRS is to suceed we need to turn it into a solution and Bluetooth and a PC are the ideal combination to achieve this ideal. Add Bluetooth to GPRS and you quickly start to experience a new era of convenience and connectivity.” 4. GPRS PLATFORMS 5. SERVICE ACCESS To take advantage of the GPRS service the Configuring hardware and software to work user would need the following: with GPRS will be a relatively simple transition as the technology supports
  6. 6. 1. A terminal that supports GPRS, typically are sent in all different directions, many are a mobile phone; to reach the same destination. It is inevitable that on or more of these packets 2. A subscription to a mobile phone are lost or corrupted over the radio link. network that supports GPRS and use of GPRS must be enabled for that user; 3. Knowledge of how to send and receive GPRS information using their specific 6.4 Absence of store and forward model of mobile device including method When a Short Message Service message hardware and software configuration; has been sent, it is stored. If the destination With Short Message Service the destination is unavailable at the time i.e. the phone is to send data was often another mobile switched off or out of reception range, the phone but with GPRS it is likely that it will be message is forwarded to a storing an Internet address. As soon as GPRS is mechanism at the other end. When the activated and enabled, the user immediately destination becomes available, it retrieves has access to all Internet applications the message. There is no storage providing a critical mass of functions. mechanism stored in the GPRS standard apart from the incorporation of 6. GPRS LIMITATIONS interconnection links between Short Message Service and GPRS. 6.1 Limited cell capacity The radio resources are limited and they can be deployed for different uses. Use for one purpose precludes simultaneous use for another. E.g. There are shared network resources used for both GPRS and voice calls. There is an adverse affect but the true impact depends upon the number of 7. GPRS TIMESCALES timeslots, if there are any that are reserved Like the GSM standard, the introduction of for exclusive use o GPRS. the GPRS standard will take place in phases. In Phase 1 there is no support for 6.2 Slow speeds sending simultaneously. Phase 2 supports, It was discussed in the User Features incorporation of technologies such as section, subsection 2.1 that it is unlikely that Enhanced Data rates information to several the initial and remaining speed will GPRS users for GSM Evolution as well as approximate around 160 kbps or above. It Point-to- sending information to a single is unheard of that the network operator will user is supported, but higher data rates allow a single user to take over all eight through the Multipoint support. The stages timeslots with no error correction of development like any other technology whatsoever. The network constraints and included the following: standardization; terminals also affect the transmission infrastructure development; network trials; speeds. contracts placed; network roll out; availability of terminals; application development; marketing of the service etc. 6.3 Delays in transit The stages are set out in figure. 4. Potential transit delays occur, due to the way that packets are sent. As the packets Figure 4. Timescales of GPRS [4] DATE MILESTONE Throughout Network operators place trial and commercial contracts for GPRS 1999 infrastructure. 2000 Incorporation of GPRS infrastructure into GSM networks. Summer of First trial of GPRS services become available. 2000 Typical single user throughput is likely to be 28 kbps. BT Cellnet and T-Mobile both launch trial services. Start of 2001 Basic GPRS capable terminals begin to be available in commercial quantities.
  7. 7. Throughout Network operators launch GPRS services commercially and roll out 2001 GPRS. Vertical market and executive GPRS early adopters begin using it regularly for non voice communication. 2001/2002 Typical single user throughput is likely to be 56 kbps. New GPRS specific, higher bitrates, greater network capacity solutions, more capable terminals become available fuelling GPRS usage. 2002 Typical single user throughput is likely to be 112 kbps. GPRS phase 2/EDGE begins to emerge in practice. 2002 GPRS is routinely incorporated into GSM mobile phones and has reached critical mass in terms of usage (this is equivalent to the status of Short Message Service in 1999) 2002/2003 UMTS arrives commercially. 8. REFERENCES [6] Mouly, M. The GSM system for mobile [1] Mobile Edge, StealthNet Europe. communications Palaiseau (1992) hnology.htm [7] Halonen T, GSM, GPRS and EDGE last accessed on 23rd November 2003 Performance- Evolution towards 3g. John Wiley & Sons (2003) [2] Rysavy P, General Packet Radio Service. GSM Data Today. [8] Anderson ChristofferGPRS and 3G Rysavy Research (1998) Wireless Applications: Professional developer’s guide [3] What is GPRS? Tony Dennis, Dollergate John Wiley & Sons (2001) Publishing [9] Stuckman P. The GSM Evolution- last accessed on 23rd November 2003 Mobile Packet Data Services. John Wiley & Sons (2002) [4] Buckingham, S. Yes 2 GPRS, Mobile GPRS white papers. [10] Sanders G, GPRS Networks. John (august 2000) Wiley & Sons(2003) [5] Wireless Logic, Embracing the mobile [11] Tisal J. The GSM network. John Wiley edge and Sons Ltd. (2001) ucts/products_airtime.htm Accessed on 23rd November 2003-11-26