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 LicenseCompany Paid (Pounds) ATIW (3)4,384,700,000 BVodafone5,964,000,000 CMM024,030,100,000 DOne2One (T-Mobile)4,003,600,000 EOrange4,095,000,000

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 ChannelUse of the Channel 0Voice 1AAAABBABBAAAAFA 2Voice 3AAABAABAAAFAAAA 4AAAFAFAFFFAFFFFB 5BBBBABABAFFFFFFF 6Voice 7FFAFFAFFABABBBBB 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 ClassDownlinkUplinkMaximum Active 1112 2213 3223 4314 5224 6324 7334 8415 9325 10425 11435 12445

13. General Packet Radio Service

14. GPRS coding schemes  Depending on environment one of the following coding schemes are used SchemeMax Throughput per 1 Time SlotError Checking CS-18 KbpsGood CS-212 KbpsGood CS-314.4 KbpsModerate CS-420 KbpsPoor 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. 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)http://www.ovum.com/go/content/c,36230

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)www.simplewire.com/support/faq/issue/369160855.html 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