Transcript General Packet Radio Service Justin Champion Room C208 - Tel: 3273

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
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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

General Packet Radio Service
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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
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This left little available for infrastructure upgrades
Also devices were not ready to be used with 2 Mbps
License
Company
Paid (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
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General Packet Radio Service (GPRS)

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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
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General Packet Radio Service (GPRS)
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Features
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Higher connections speeds
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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
General Packet Radio Service
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GPRS Devices
 In
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 All
the standard there are three types of GPRS devices
A

Capable of Simultaneous data transfer and voice communications

Automatic switching between voice and data calls. This will need to
be configured on the device itself

Switching between data and voice operated by the device user
manually.
B
C
of these standards are backwards compatible with the
GSM networks for voice communications
General Packet Radio Service
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GPRS
 Relies
on the fact that Internet communications are
bursty in nature
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 All
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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.
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
General Packet Radio Service
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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
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Resources have to be allocated even if you are not saying anything
As paths between parties are already worked out and agreed realtime communications can take place better
General Packet Radio Service
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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 Users
A = User 1
B = User 2
F = User 3
In this instance we
have 3 voice calls and
5 users receiving data
General Packet Radio Service
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GPRS Channel Breakdown Continued
 A channel
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Can only be shared between other GPRS users
It can not be allocated in that time slot for GSM voice calls
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which is being used for GPRS data
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
General Packet Radio Service
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GPRS Multi slot classes
Class
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
General Packet Radio Service
General Packet Radio Service
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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
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GPRS network layers
General Packet Radio Service
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GPRS network layers
 Sub
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Network Dependent Convergence Protocol (SNDCP)
Provides services to the higher layers
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 BSS
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Compression
Connectionless, connection orientated services
Multiplexing
Segmentation
GPRS Application Protocol (BSSGP)
Allows
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Maps a SGSN to a BSS
Control information between a BSS and a SGSN
 BSS
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Refers to a base station and an associated Base station controller
General Packet Radio Service
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GPRS Infrastructure
 As
discussed earlier GPRS build upon the GSM networks.
 Network elements need changing
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Base stations
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Requires a software upgrade
Base station controller
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Requires a software upgrade
 New parts need adding
 Serving GPRS Support Node (SGSN)
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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
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GPRS Infrastructure continued
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Gateway GPRS Support Node (GGSN)
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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
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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
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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
General Packet Radio Service
General Packet Radio Service
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Packet Control Unit (PCU)
 Logically
part of the Base station controller
 Responsible for the radio interface of GPRS
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GPRS and SMS
 SMS
messages are sent in GPRS as a part of the
normal data channels
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In GSM they are usually sent via the control channels
 Why
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This changes has taken place ready for the Multimedia
Messaging service
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Due to the size of the messages
General Packet Radio Service
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Current Supported Protocols
 IP
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Internet Protocol
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Connectionless protocol, which delivers based on best effort
Widely used in most networks
 X.25
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Connection orientated communications
Reliability built in with error checking the header
Uses Virtual circuits
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Intended for terminal services
Still used but is being replaced by other technologies
General Packet Radio Service
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General Packet Radio Service Problems
 Initial
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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
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 This
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problems existed in respect to the GPRS device
Potentially this was an issue around how much the advertising of the
WAP services cost operators
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)
General Packet Radio Service
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IP address packet routing
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The intention is to give each device a unique IP address
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This reduces the amount of address translation which is required
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Address is issued by the GGSN
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One address being used all the way across the network
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
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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
General Packet Radio Service
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IP Address
 Why
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does it change ?
IP packet routing is based around subnets
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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
General Packet Radio Service
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IP Address
 Consider
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If a single IP address was retained by a device how do you route
data when it moves from the home location?
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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
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what will happen with a large network
With your packet being forwarded from your original address to
your new one
 This is an additional load on the infrastructure
IPv6
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Possible future use and will be discussed in a later lecture
General Packet Radio Service
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IP Address
 As
you connect and disconnect you will be given a new
IP Address
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Using Dynamic Host Configuration Protocol (DHCP)
Consider if you disconnect because an handover does not work
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What happens to your packets, does another device get them ?
Addresses Issues
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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
General Packet Radio Service
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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
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1 Billion worldwide devices are predicted by 2005
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(www.simplewire.com/support/faq/issue/369160855.html, 2004)
4 Billion potential IP address
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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
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Key Points of lecture
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GPRS increases the data rate of GSM
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Uses current GSM infrastructure, with small changes
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Additional servers
How GPRS operates
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20-40 Kbps
Breaking the time frame into parts
Issue of IP packets in a network
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Changing IP Addresses
Consequences if you don’t
General Packet Radio Service
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Summary
 Why
we need the technology
 What it is
 Infrastructure changes