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General Packet Radio Service. Justin Champion Room C208 - Tel: 3273 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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General packet radio service

General Packet Radio Service

Justin Champion

Room C208 - Tel: 3273

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General Packet Radio Service

  • Contents

    • Why do we need it

    • Details of GPRS

    • Sending of Packets

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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

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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

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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

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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

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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

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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

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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

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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

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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

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General Packet Radio Service

  • GPRS Multi slot classes

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General Packet Radio Service

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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

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General Packet Radio Service

  • GPRS network layers

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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

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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

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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

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General Packet Radio Service

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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

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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

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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

        (,36230, 2003)

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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

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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

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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

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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

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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

        • (, 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

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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

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General Packet Radio Service

  • Summary

    • Why we need the technology

    • What it is

    • Infrastructure changes

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