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GPRS: General packet radio service

About this computer paper-presentations : (GPRS)
          This paper discusses about GPRS (general packet radio service) a relatively new technology that offers a packet based radio service with mobile networks. The task in this paper proves the evolving of GPRS from GSM to fulfill the technologies evolution from voice to data. This also serves the needs of fast generation with high speed data access using mobile networks. The later stage of paper shows the special features of GPRS such as band width requirements with low cost. The approach of this paper proves the development of GPRS over the years towards the applications like audio, web browsing, internet email and moving images.

GPRS: General packet radio service


GPRS (General Packet Radio Service) is built upon the worldwide accepted and successful GSM (Global System for Mobile Communications) Technology. GPRS involves overlaying a packet based air interface on the existing circuit switched GSM network. This gives the user an option to use a packet-based data service. To supplement a circuit-switched network architecture with packet switching is quite a major upgrade.
Evolving from GSM to GPRS means to fulfill the technological evolution from voice to data.
With maximum transmission rates of 170 k bits/s GPRS transports data more than fifteen times faster than GSM. GPRS only uses network resources and bandwidth during data transmission, so the operator saves network extension costs. It is therefore well suited for a range of personalized applications and value-added services that require bulky and bursty data transfer such as mobile Internet, electronic banking, and location-based services.

2. GPRS Technology
General Packet Radio Service or GPRS is relatively a new technology that offers packet based radio service to mobile networks. Designed to supplement the existing mobile technologies, like GSM, CDMA, TDMA etc, GPRS aims to provide anytime-anywhere “always-on” network connections to mobile devices. GPRS also enables mobile networks to provide speeds much higher than those offered by GSM alone.
 Though GSM uses circuit switching like a telephone line, data transfer over GSM is not quite the same as that over the PSTN line. For each of our data requests (Over GSM), first, a connection is established without network, our request sent, the data received and then, and this is important, that call is disconnected. Thus, we have a dedicated connection as long as a transaction lasts, but not in between transactions. This is designed to overcome its bandwidth wastage limitation and ensure that our connectivity costs don’t spiral up as there can be, and generally are, long periods of inactivity between consecutive transactions.
The savings in costs, however, are more than compensated by long delays associated with each transaction and subsequent data transfer- a major part of which is the time spent in trying to establish a connection with the network. Add to it the fact that GSM offers a maximum speed of 14 kbps only, or 1/4th speed of your dial-up connect, and the reason why mobile Internet hasn’t taken off, becomes clear.
GPRS, though, has the potential to change that. Using GPRS and its packet switching technique, both the mobile device and the network send packets as and when they have to, without having to wait for the connection to be established.

Also GPRS can theoretically offer speeds up to three times your dial-up speeds or 171.2 kbps (wherein all timeslots are allocated to a single user). Such high speeds though are unlikely to be seen, as networks would share the available bandwidth between multiple users.

3. Implementing GPRS
Integrating GPRS into a GSM network does not involve any major changes to the GSM architecture.  A new class of nodes, GSN (GPRS support nodes) has been introduced two types of GSNs defined. A SGSN (serving GPRS support node) interacts with the mobile devices and is responsible for delivery packets from and to these devices.
The SGSN communicates with registers (same as in GSN) to access the required information.  A network would have as many as SGSNs as necessary to GPRS enable the required network
 A GGSN (Gateway GSN) is an interface between GPRS enabled network and the external packet switching network. The GGSN is responsible for all the conversions necessary for transport of data from the external network to the internal one and vice versa. This involves all the data packets as well the source/ destination addresses from one standard to another. The SGSNs communicate with the GGSN to provide access to the external network to their subscribers. A network would have as many as GGSNs as the number of external packet switching data networks linked to it.

4. Circuit switching and packet switching network
4.1. Circuit Switching

While using circuit switching the sender seeks a connection right unto the receiver before it begins transmitting. Data transmission begins only after the sender has verified that a dedicated connection to the receiver exists. This means the circuit-switching networks suffer from “hunting delays”, the time spent to establish a connection with the receiver. But once the connection has been established, communication is, for all practical purposes, instantaneous. The connection is maintained- even if no data transmission is taken place-until either side explicitly terminates it. Thus, all information travels the same path from the sender to the receiver and arrives in the same order as it was sent.

4.2. Packet Switching

 Using packet switching, however, eliminates the need to establish a connection before transmission can begin. The information to be sent is broken down into packets (of fixed size) and sent on to the network one after the other. Each packet completes the journey to the receiver independently of the others- routing equipment along the way decide which path the packet must take, depending on the current network conditions and the other factors.
This means that packets may take different paths in reaching the receivers and may even arrive out of order –the job of reassembling them in the proper order is that of the receiver. Thus, though hunting delays are absent from packet switching networks, they do suffer from performance related problems.

Advantages of Packet Switching over Circuit Switching network

1.    Packet Switching Networks has dynamic allocation of bandwidth - packets are sent to the physical medium as and when there is data to be sent
2.     It allows the bandwidth to be used for other purposes during “pauses” between “conversations”. Contrast this with the circuit switching technique where in the path between the sender and receiver is reserved for their exclusive use, which means that the bandwidth is wasted during “moments of silence”.

5.    Features:
5.1.    User features :
The real advantage of GPRS is that it provides an ‘ALWAYS – ON’ connection between mobile terminal and the network. ‘Always – on’ does not mean that there is always a steady stream data connection; It just means that, because data packets can be transmitted almost immediately i.e., instant IP connectivity, there is no costly connection time. Many current 2G information services require a data connection over voice line. As a result, users are charged by the minute for data services. This would not be necessary with GPRS.
    SPEED is main advantage over existing networks. Using all 8 TDMA time slots in radio interface, a maximum speeds of up to 171.2 K bit/s are possible, that’s about 3 times faster than 56K modem and about 10 times faster CSD(Circuit Switched Data) transfers currently used.
HIGHER BANDWIDTH enables applications such as low quality video monitoring or music download.
5.2. Network features:
Packet switching replaces the circuit switched transfer mechanism of GSM. Just like data transfers over internet, GPRS splits information into separate related data packets that are transmitted and reassembled at the termination. This allows the operators to implement IP (Internet Protocol) based infrastructure for tomorrows 3G voice and data applications.
SPECTRUM is used efficiently because GPRS resources are only allocated when there is actual data transfer, thus sharing the same limited radio resource among all mobile devices in a cell which frees up idle bandwidth that would have otherwise been wasted.

6. Working of GPRS:
Since the main goal of GPRS is to provide an intermediate step towards 3G, it needs to be both straightforward so that it can deploy on existing systems and also provide a logical upgrade path to 3G. However it is very important to note that GPRS signaling and data transfer does not in fact travel through GSM networks. The GSM network is only contacted for table look up in Location Registers so that GPRS can find user profiles on the existing network.

The radio spectrum in the bands 890-915 MHz for the uplink (mobile station to base station) and 935-960 MHz for the downlink has been reserved in Europe some regions in Asia Pacific for mobile networks. At least 10 MHz in each band was reserved explicitly for GSM. This 2x25 MHz spectrum is divided into 200 kHz carrier frequencies using FDMA. One or more carrier frequencies are assigned to individual base stations, and each carrier is divided into eight time slots using TDMA. Groups of eight consecutive time slots form TDMA frames; with a duration of 4.615 ms. A transmission channel occupies one time slot position within a TDMA frame. TDMA frames of a particular carrier frequency are numbered, and both the mobile station and the base station are synchronized on this number. Larger frames are formed from groups of 26 and 51 TDMA frames (there are also larger groups), and position within such frames defines the type and function of a channel. GPRS sends packetized air traffic over one to eight time slots using time division multiple access. This can be shared with other users. The receiver takes these packets and sends them over public land mobile networks using IP backbones. The packets can then be rooted like any other IP datagram, onto other public data networks like the internet.

7. GPRS network nodes:

     Since existing network nodes use circuit switch technology, they cannot handle packet traffic. Base stations for instance, would have to be upgraded to include packet control units, mobility management, and security features. In addition to deploy GPRS on GSM, two kinds of network nodes are needed:

1)    Serving GPRS support node (SGSN) :
•    Delivers packets to mobile stations within service area
•    Detects new GPRS mobile stations
•    Queries home location register to get user profile data
•    Keeps track of mobile stations.

2)    Gateway GPRS support node (GGSN) :
•    Interfaces with external IP networks
•    Maintains routing information used to tunnel packets to the right SGSN.
One GGSN serves many SGSNs.
8. Applications for GPRS
A wide range of corporate and consumer applications are enabled by nonvoice mobile services such as SMS and GPRS. This section will introduce those that are particularly suited to GPRS.
8.1. CHAT
Chat can be distinguished from general information services because the source of the information is a person with chat whereas it tends to be from an Internet site for information services. The "information intensity"- the amount of information transferred per message tends to be lower with chat, where people are more likely to state opinions than factual data. In the same way as Internet chat groups have proven a very popular application of the Internet, groups of likeminded people- so called communities of interest- have begun to use nonvoice mobile services as a means to chat and communicate and discuss. GPRS will not however support point to multipoint services in its first phase, hindering the distribution of a single message to a group of people.
A wide range of content can be delivered to mobile phone users ranging from share prices, sports scores, weather, flight information, news headlines, prayer reminders, lottery results, jokes, horoscopes, traffic, and location sensitive services and so on. This information need not necessarily be textual- it may be maps or graphs or other types of visual information. The length of a short message of 160 characters suffices for delivering information when it is quantitative- such as a share price or a sports score or temperature. When the information is of a qualitative nature however, such as a horoscope or news story, 160 characters is too short other than to tantalize or annoy the information recipient since they receive the headline or forecast but little else of substance. As such, GPRS will likely be used for qualitative information services when end users have GPRS capable devices, but SMS will continue to be used for delivering most quantitative information services.
Still images such as photographs, pictures, postcards, greeting cards and presentations, static web pages can be sent and received over the mobile network as they are across fixed telephone networks. It will be possible with GPRS to post images from a digital camera connected to a GPRS radio device directly to an Internet site, allowing near real-time desktop publishing.

Over time, the nature and form of mobile communication is getting less textual and more visual. The wireless industry is moving from text messages to icons and picture messages to photographs and blueprints to video messages and movie previews being downloaded and on to full blown movie watching via data streaming on a mobile device.
Sending moving images in a mobile environment has several vertical market applications including monitoring parking lots or building sites for intruders or thieves, and sending images of patients from an ambulance to a hospital. Videoconferencing applications, in which teams of distributed sales people can have a regular sales meeting without having to go to a particular physical location, is another application for moving images.
Using Circuit Switched Data for web browsing has never been an enduring application for mobile users. Because of the slow speed of Circuit Switched Data, it takes a long time for data to arrive from the Internet server to the browser. Alternatively, users switch off the images and just access the text on the web, and end up with difficult to read text layouts on screens that are difficult to read from. As such, mobile Internet browsing is better suited to GPRS.
8.6. AUDIO
Despite many improvements in the quality of voice calls on mobile networks such as Enhanced Full Rate (EFR), they are still not broadcast quality. There are scenarios where journalists or undercover police officers with portable professional broadcast quality microphones and amplifiers capture interviews with people or radio reports dictated by themselves and need to send this information back to their radio or police station. Leaving a mobile phone on, or dictating to a mobile phone, would simply not give sufficient voice quality to allow that transmission to be broadcast or analyzed for the purposes of background noise analysis or voice printing, where the speech autograph is taken and matched against those in police storage. Since even short voice clips occupy large file sizes, GPRS or other high speed mobile data services are needed.
Internet email services come in the form of a gateway service where the messages are not stored, or mailbox services in which messages are stored. In the case of gateway services, the wireless email platform simply translates the message from SMTP, the Internet email protocol, into SMS and sends to the SMS Center. In the case of mailbox email services, the emails are actually stored and the user gets a notification on their mobile phone and can then retrieve the full email by dialing in to collect it, forward it and so on.
Upon receiving a new email, most Internet email users do not currently get notified of this fact on their mobile phone. When they are out of the office, they have to dial in speculatively and periodically to check their mailbox contents. However, by linking Internet email with an alert mechanism such as SMS or GPRS, users can be notified when a new email is received.
This application integrates satellite positioning systems that tell people where they are with nonvoice mobile services that let people tell others where they are. The Global Positioning System (GPS) is a free-to-use global network of 24 satellites run by the US Department of Defense. Anyone with a GPS receiver can receive their satellite position and thereby find out where they are. Vehicle positioning applications can be used to deliver several services including remote vehicle diagnostics, ad-hoc stolen vehicle tracking and new rental car fleet tariffs.
The Short Message Service is ideal for sending Global Positioning System (GPS) position information such as longitude, latitude, bearing and altitude. GPS coordinates are typically about 60 characters in length. GPRS could alternatively be used.
When mobile workers are away from their desks, they clearly need to connect to the Local Area Network in their office. Remote LAN applications encompasses access to any applications that an employee would use when sitting at their desk, such as access to the intranet, their corporate email services such as Microsoft Exchange or Lotus Notes and to database applications running on Oracle or Sybase or whatever. The mobile terminal such as handheld or laptop computer has the same software programs as the desktop on it, or cut down client versions of the applications accessible through the corporate LAN. This application area is therefore likely to be a conglomeration of remote access to several different information types- email, intranet, and databases. This information may all be accessible through web browsing tools, or require proprietary software applications on the mobile device. The ideal bearer for Remote LAN Access depends on the amount of data being transmitted, but the speed and latency of GPRS make it ideal.

As this generic term suggests, file transfer applications encompass any form of downloading sizeable data across the mobile network. The source of this information could be one of the Internet communication methods such as FTP (File Transfer Protocol), telnet, http or Java- or from a proprietary database or legacy platform. It therefore requires a high speed mobile data service such as GPRS, EDGE or 3GSM to run satisfactorily across a mobile network.
Home automation applications combine remote security with remote control. Basically, you can monitor your home from wherever you are- on the road, on holiday, or at the office. Not only can you see things at home, but you can do things too. You can program your video, switch your oven on so that the preheating is complete by the time you arrive home (traffic jams permitting) and so on. Your GPRS capable mobile phone really does become like the remote control devices we use today for our television, video, hi-fi and so on. A key enabler for home automation applications will be Bluetooth, which allows disparate devices to interwork.

9. Limitations of GPRS
It should already be clear that GPRS is an important new enabling mobile data service which offers a major improvement in spectrum efficiency, capability and functionality compared with today's nonvoice mobile services. However, it is important to note that there are some limitations with GPRS, which can be summarized as:
GPRS does impact a network's existing cell capacity. There are only limited radio resources that can be deployed for different uses- use for one purpose precludes simultaneous use for another. For example, voice and GPRS calls both use the same network resources. The extent of the impact depends upon the number of timeslots, if any, that are reserved for exclusive use of GPRS. However, GPRS does dynamically manage channel allocation and allow a reduction in peak time signalling channel loading by sending short messages over GPRS channels instead.
Achieving the theoretical maximum GPRS data transmission speed of 172.2 kbps would require a single user taking over all eight timeslots without any error protection. Clearly, it is unlikely that a network operator will allow all timeslots to be used by a single GPRS user. Additionally, the initial GPRS terminals are expected be severely limited- supporting only one, two or three timeslots.
GPRS packets are sent in all different directions to reach the same destination. This opens up the potential for one or some of those packets to be lost or corrupted during the data transmission over the radio link. The GPRS standards recognize this inherent feature of wireless packet technologies and incorporate data integrity and retransmission strategies. However, the result is that potential transit delays can occur.
Whereas the Store and Forward Engine in the Short Message Service is the heart of the SMS Center and key feature of the SMS service, there is no storage mechanism.
Incorporated into the GPRS standard, apart from the incorporation of interconnection links bet ween SMS and GPRS.

10. Conclusion
 GPRS, which uses packet switching network, offers a better data transfer rate and proved to be a better communication system than circuit switched GSM. GPRS enables an existing GSM network to communicate with any applications and/or network that uses packet switching. Thus it allows mobile networks to connect to the INTERNET 2.5G GPRS is considered to be the next step towards the 3G networks. As it offers pretty good speeds GPRS has the potential to move beyond cell phones and move into the PC world. Laptops connected to GPRS phones would offer speeds fast, and may be even faster, than our PC connected to our landline.

11. References:

                          Electronics for u, sept 2003
                          Digit-mobile communications.
BY: G.SIVA NARAYANA REDDY                      T.UPENDRA

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