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General Packet Radio Service

General Packet Radio Service. Justin Champion Room C208 - Tel: 3273 www.staffs.ac.uk/personal/engineering_and_technology/jjc1. General Packet Radio Service. Contents Why do we need it Details of GPRS Sending of Packets. General Packet Radio Service. Value Added Services

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General Packet Radio Service

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  1. General Packet Radio Service Justin Champion Room C208 - Tel: 3273 www.staffs.ac.uk/personal/engineering_and_technology/jjc1

  2. General Packet Radio Service • Contents • Why do we need it • Details of GPRS • Sending of Packets

  3. General Packet Radio Service • Value Added Services • Operators have seen the use of data as a new source of revenue • The potential for data use is • To sell the users the data applications • To charge them for data needed to use them • To charge other developers to allow the applications on to the network

  4. General Packet Radio Service • 3G data use • Although the UK operators have bought licensees to use 3G the infrastructure is not ready • The operators paid a lot for the radio spectrum licenses • This left little available for infrastructure upgrades • Also devices were not ready to be used with 2 Mbps

  5. General Packet Radio Service • General Packet Radio Service (GPRS) • This standard was agreed by ETSI March 1998 • It is designed to allow data communication to take place within the existing GSM infrastructure. • A few additional servers are added to the network to allow this and these will be discussed later • This is described as being a 2.5G technology • To use GPRS you will need a GPRS enabled device • Existing GSM devices will not be able to make use of the additional features

  6. General Packet Radio Service • General Packet Radio Service (GPRS) • Features • Higher connections speeds • Theoretical Maximum of 171 Kbps • Interference • Distance from transmitter • All GSM channels would have to be dedicated to GPRS communications • This speed also does not take into account any error-correction • Does not consider a device uploading data • Actually speeds with conditions taken into account is theoretically a maximum of 53.6 Kbps • Studies have show the average is usually about 30 – 40 Kbps • Always on Data communications • No delay in setting up a data communication

  7. General Packet Radio Service • GPRS Devices • In the standard there are three types of GPRS devices • A • Capable of Simultaneous data transfer and voice communications • B • Automatic switching between voice and data calls. This will need to be configured on the device itself • C • Switching between data and voice operated by the device user manually. • All of these standards are backwards compatible with the GSM networks for voice communications

  8. General Packet Radio Service • GPRS • Relies on the fact that Internet communications are bursty in nature • A large amount of data will be received and the user will process it before requesting more i.e. a web page • A single voice circuit will from GSM will be broken into smaller parts and the GPRS data is sent on this circuit. • All data is sent in packets • Data must be broken into small packets • These packets are re-assembled at the destination • These packets add an overhead in the form of the packet header • Lower resource requirements than circuit switched communications

  9. General Packet Radio Service • Packet/Circuit Transfer • Consider a packet as being an letter in the post • Packets can be sent and only when the packet is being looked at to get the address or moved will resources be allocated • Issues • Packet headers reduces the amount of actual data sent • Packets are for the most part currently not good with real-time data • Consider a circuit as being a telephone call • A circuit is created between you and the receiver • All communications are sent through this circuit • Resources have to be allocated even if you are not saying anything • As paths between parties are already worked out and agreed real-time communications can take place better

  10. General Packet Radio Service • GPRS Channel Breakdown • Data Users • A = User 1 • B = User 2 • F = User 3 In this instance we have 3 voice calls and 5 users receiving data

  11. General Packet Radio Service • GPRS Channel Breakdown Continued • A channel which is being used for GPRS data • Can only be shared between other GPRS users • It can not be allocated in that time slot for GSM voice calls • Even if part of the time slot is available • The use of GPRS will reduce the amount of voice calls that can be made on that cell • With enough data calls a cell will become useless for voice callers, which require exclusive access to the time slots

  12. General Packet Radio Service • GPRS Multi slot classes

  13. General Packet Radio Service

  14. General Packet Radio Service • GPRS coding schemes • Depending on environment one of the following coding schemes are used Schemes CS-1 and CS-2 are usually used

  15. General Packet Radio Service • GPRS network layers

  16. General Packet Radio Service • GPRS network layers • Sub Network Dependent Convergence Protocol (SNDCP) • Provides services to the higher layers • Compression • Connectionless, connection orientated services • Multiplexing • Segmentation • BSS GPRS Application Protocol (BSSGP) • Allows • Maps a SGSN to a BSS • Control information between a BSS and a SGSN • BSS • Refers to a base station and an associated Base station controller

  17. General Packet Radio Service • GPRS Infrastructure • As discussed earlier GPRS build upon the GSM networks. • Network elements need changing • Base stations • Requires a software upgrade • Base station controller • Requires a software upgrade • New parts need adding • Serving GPRS Support Node (SGSN) • Has VLR functionality • Authorise attached users • Details recorded of data packets to be charged for • Session Management • Router for packets which may be lost during a handover during a data call

  18. General Packet Radio Service • GPRS Infrastructure continued • Gateway GPRS Support Node (GGSN) • Is the connection into the GPRS network • It carries out all translations that area required • Firewall for the network • Collates data regarding the amount of packets received • Potentially in the future this will allow for competing GGSN’s in a network! Free market choosing either the cheapest or most reliable GGSN! • There are 3 types of GGSN • A – Near Future/Now • The GGSN becomes part of its own ISP and provides Internet services. The devices will be assigned IP address using DHCP. • B – Now • The SSGN always selects the same GGSN to do the Internet work. The configuration will be done dynamically and on a temporary basis • C – Future • This allows a private company to have its own GGSN, with an encryption key so that only authorised devices can gain access. i.e. a VPN into a network, constant email access etc

  19. General Packet Radio Service

  20. General Packet Radio Service • Packet Control Unit (PCU) • Logically part of the Base station controller • Responsible for the radio interface of GPRS • GPRS and SMS • SMS messages are sent in GPRS as a part of the normal data channels • In GSM they are usually sent via the control channels • Why • This changes has taken place ready for the Multimedia Messaging service • Due to the size of the messages

  21. General Packet Radio Service • Current Supported Protocols • IP • Internet Protocol • Connectionless protocol, which delivers based on best effort • Widely used in most networks • X.25 • Connection orientated communications • Reliability built in with error checking the header • Uses Virtual circuits • Intended for terminal services • Still used but is being replaced by other technologies

  22. General Packet Radio Service • General Packet Radio Service Problems • Initial problems existed in respect to the GPRS device • When launched there was only a few compatible devices • These had poor features and terrible battery life • There was nothing to use the increased data rate • Limited advertising of the features of GPRS • Potentially this was an issue around how much the advertising of the WAP services cost operators • This is now changing • O2 have seen a 25% growth in usage of GPRS data from Jan to June 2003 (http://www.ovum.com/go/content/c,36230, 2003)

  23. General Packet Radio Service • IP address packet routing • The intention is to give each device a unique IP address • This reduces the amount of address translation which is required • One address being used all the way across the network • Address is issued by the GGSN • Based upon the DHCP protocol on a temporary basis • Issue that needs considering is what happens when you move GGSN? • Packets which are sent to you at the old address • Another device may receive your data • Roaming • This is a particular issue when using the device and moving around • A single address is not always attached to a device • If communications are lost then you get a new IP address issued

  24. General Packet Radio Service • IP Address • Why does it change ? • IP packet routing is based around subnets • The subnet directs the packet to roughly where device is • The network then directs to the actual machine based on the subnet • IP addresses are made up of two parts • Network Address (the subnet) • Host Address • The subnet part will get the packet to the correct location • Host address will get to the actual device

  25. General Packet Radio Service • IP Address • Consider what will happen with a large network • If a single IP address was retained by a device how do you route data when it moves from the home location? • i.e. I visit London for the weekend with my device • Consider • What happens when I visit Germany with my device • Mobile IP is a possible solution • With your packet being forwarded from your original address to your new one • This is an additional load on the infrastructure • IPv6 • Possible future use and will be discussed in a later lecture

  26. General Packet Radio Service • IP Address • As you connect and disconnect you will be given a new IP Address • Using Dynamic Host Configuration Protocol (DHCP) • Consider if you disconnect because an handover does not work • What happens to your packets, does another device get them ? • Addresses Issues • Two options • Private - only available within the network • Uses Network address translator (NAT) to get data from the Internet • Public – Available from outside of the network • Effectively the node is a part of the Internet • All of the PC security issues are still valid

  27. General Packet Radio Service • Public IP considerations • This does allow faster access to the Internet • IP Security (IPSEC) can be used • Consider though how many devices would need these addresses • 1 Billion worldwide devices are predicted by 2005 • (www.simplewire.com/support/faq/issue/369160855.html, 2004) • 4 Billion potential IP address • Mobile devices could take a very large chunk of the address space • In fact too much this would not leave enough for other uses

  28. General Packet Radio Service • Key Points of lecture • GPRS increases the data rate of GSM • 20-40 Kbps • Uses current GSM infrastructure, with small changes • Additional servers • How GPRS operates • Breaking the time frame into parts • Issue of IP packets in a network • Changing IP Addresses • Consequences if you don’t

  29. General Packet Radio Service • Summary • Why we need the technology • What it is • Infrastructure changes

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