GPRS GSM
8 GPRS 8.1 introduction to GPRS 8.1.1 What is GPRS ? GPRS (General Packet Radio Servics) ) is a mobile By Nabeel Yousef Saleh data service available to users of GSM mobile phones. It is often described as "2.5G", that is, a technology between the نبيل يوسف صالح second and third generations of mobile telephony • Part of GSM phase 2+ • General -> not restricted to GSM use • Packet Radio -> enables packet mode communication over air • Service, not System -> existing BSS (partially also NSS) infrastructure is used • Requires many new network elements into NSS • Provides connections to external packet data networks (Internet, X.25) • It provides moderate speed data transfer, by using unused TDMA channels in the GSM network. • The theoretical limit for packet switched data is 171.2 kbit/s .A realistic bit rate is 30–80 kbit/s, because it is possible to use max 4 time slots for downlink • It uses exactly the same physical radio channels as GSM, only logical GPRS radio channels are defined. 8.1.2 Use of GPRS * Different Transmission method (8PSK instead GMSK) * New coding channel (cs1 – cs2 – cs3 – cs4) * Use of multiple channel 8.1.3 New service in GPRS • point to point service (PTP) PTP connectionless network (PTP-CLNS) PTP connection oriented network (PTP-CONS) • Point to multipoint service (PTM) Point to multipoint multicast Point to multipoint group call Internet protocol multicast • Access to data network like the internet and intranet • Reading of fax and email • Receiving breaking news and complete newspaper content • Getting the latest traffic information for planned trip • Message of commercial interest 8.2 GPRS Architecture
8.2.1 GPRS Subscriber Terminals New terminals are required because existing GSM phones do not handle the enhanced air interface, nor do they have the ability to packetize traffic directly terminals will exist including a high-speed version of current phones to support highspeed data access.
1
GPRS Architecture Other GPRS PLMN GGSN
Gp Gn
SGSN BSC
Gb
Gf
MS
Gr
Gs
BTS BTS
EIR
Gc D
GGSN
Gi
HLR
MSC/VLR
Class A –Class B – Class C
8.2.2 GPRS BSS Each BSC will require the installation of one or more PCUs and a software upgrade. The PCU provides a physical and logical data interface out of the base station system (BSS) for packet data traffic. The BTS may also require a software upgrade, but typically will not require hardware enhancement. 8.2.3 GPRS Networks Node In the core network, the existing MSCs are based upon circuit-switched central-office technology, and they cannot handle packet traffic. Thus two new components, called GPRS Support Nodes, are added: • Serving GPRS Support Node (SGSN ( • Functionally connected with BSC, physically can be at MSC or BSC site • One for few BSCs or one (or few) per every BSC • One SGSN can support BSCs of several MSC sites • Main functions • Authenticates GPRS mobiles • Handles mobile’s registration in GPRS network • Handles mobile’s mobility management • Relays MO and MT data traffic • TCP/IP header compression, V.42bis data compression, error control MS- SGSN (ARQ) • Collect charging information of air interface usage Contain packet data protocol context Ciphering function Mobility management Security • Gateway GPRS Support Node (GGSN) Screening (firewall) GGSN • Typically located at one of the MSC sites • One (or few) per operator • Main functions • Interface to external data networks • Resembles to a data network router
PDN
GPRS GSM
•
• Forwards end user data to right SGSN • Routes mobile originated packets to right destination • Filters end user traffic • Collects charging information for data network usage Data packets are not sent to MS unless the user has activated the PDP address
8.2.4 GPRS Mobility Management Mobility management within GPRS builds on the mechanisms used in GSM networks. As a MS moves from one area to another, mobility management functions are used to track its location within each mobile network 8.3 WORKING OF GPRS Each voice circuit in GSM transmits the speech on a secure 14kbps digital radio link between the mobile phone and a nearby GSM transceiver station. The GPRS service joins together multiple speech channels to provide higher bandwidth data connections for GPRS data users. The radio bandwidth remains the same, it is just shared between the voice users and the data users. 8.3.1 WORKING-RADIO INTERFACE Each GSM radio transceiver uses Time Division Multiplexing to deliver eight voice circuits on one radio channel. Maximum numbers are limited by many factors including - operators radio license, interference with other nearby GSM cells, cost of equipment, capacity of radio site infrastructure etc. Each 14kbps channel may be shared by multiple 'connected' GPRS users. As a user's data requirements grow, they will use more of the available capacity within that timeslot 8.4 New Logicl Channel In GPRS • Though GPRS uses basic structure as GSM, it introduces new logical channel types for Packet Common Control Channel (PCCCH) and for Packet Dedicated Control Channel (PDCCH) 8.5 New Interface In GPRS Gb --Between the PCUSN and SGSN, using Frame Relay. Gr -- Between SGSN and HLR, extension of the Mobile Application Part (MAP). Gn -- Between SGSN and GGSN, using the GTP (tunneling) protocol Gi -- Between GGSN and PDNs (X.25 and Internet Protocol[ IP]). Gs -- Between SGSN and MSC/VLR, for some simultaneous GPRS and GSM operations. Gd -- Delivers SMS messages via GPRS (same as MAP from GSM). Gc -- Between GGSN and HLR 8.6 GPRS Conclusion GPRS provides efficient access to Packet Data Networks. Multislot operation in GPRS leads to efficient channel utilization. 3
GPRS is more effective for long data packet transmission than short ones.
8.6 References “General Packet Radio Service in GSM”, Jian Cai and David J. Goodman, Rutgers University, IEEE Communications Magazine, Oct 1997 http://www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html http://www.wsdmag.com/2000/aug2200/38-45.html “Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000. William C.Y.Lee Wireless & Cellular Telecommunications- Third Edition & PANGTEL Resources.