General Packet Radio Service

General Packet Radio Service

Justin Champion

Room C208 - Tel: 3273www.staffs.ac.uk/personal/engineering_and_technology/jjc1


ContentsWhy do we need itDetails of GPRSSending of Packets


Value Added ServicesOperators have seen the use of data as a new

source of revenueThe 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

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

LicenseLicense CompanyCompany PaidPaid (Pounds) (Pounds)

A TIW (3) 4,384,700,000

B Vodafone 5,964,000,000

C MM02 4,030,100,000

D One2One (T-Mobile) 4,003,600,000

E Orange 4,095,000,000


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

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


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


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


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


GPRS Channel Breakdown

Channel Use of the Channel

0 Voice

1 AAAABBABBAAAAFA

2 Voice

3 AAABAABAAAFAAAA

4 AAAFAFAFFFAFFFFB

5 BBBBABABAFFFFFFF

6 Voice

7 FFAFFAFFABABBBBB

Data UsersA = User 1B = User 2F = User 3

In this instance we have 3 voice calls and 5 users receiving data


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


GPRS Multi slot classesClass Downlink Uplink Maximum Active

1 1 1 2

2 2 1 3

3 2 2 3

4 3 1 4

5 2 2 4

6 3 2 4

7 3 3 4

8 4 1 5

9 3 2 5

10 4 2 5

11 4 3 5

12 4 4 5


GPRS coding schemes Depending on environment one of the following coding

schemes are used

Scheme Max Throughput per 1 Time Slot Error Checking

CS-1 8 Kbps Good

CS-2 12 Kbps Good

CS-3 14.4 Kbps Moderate

CS-4 20 Kbps Poor

Schemes CS-1 and CS-2 are usually used

General Packet Radio Service GPRS network layers

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

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

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


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


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


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)


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


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


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


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


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

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


Summary Why we need the technology What it is Infrastructure changes

General Packet Radio Service

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