GPRS — A revolution in Data services

General Packet Radio Service (GPRS) provides packet data services to the Global System for Mobile communications (GSM) and Wideband Code Division Multiple Access (WCDMA) Systems. It provides a basic solution for Internet Protocol (IP) communication between Mobile Stations (MSs) and the Internet, corporate Local Area Networks (LAN), or operators’ service networks .

GPRS provides the following services:

  • Efficient transport of packets in the cellular network
  • Efficient use of valuable radio resources
  • Flexible service, with prepaid or postpaid charging based on content, volume, or session duration
  • Fast setup and access time
  • Simultaneous CS and Packet-Switched (PS) services, which means coexistence without disturbance
  • Connectivity to other external Packet Data Networks (PDNs) using IP
  • Wireless Application Protocol (WAP) browsing and Multimedia Messaging Service (MMS)

GPRS System Architecture :

There are mainly below areas are defined in system for GPRS converage.

PLMN Area

Each operator providing GPRS services has its own PLMN. A PLMN is identified by the Mobile Country Code (MCC) and the Mobile Network Code (MNC).

SGSN Service Area

An SGSN area, which consists of one or more RA(Routing Area)as, is the region served by the same SGSN. It is either a GSM SGSN area, a WCDMA Systems SGSN area, or both (in a dual access SGSN). An SGSN area does not have to coincide with an MSC/VLR area. An SGSN pool area is the region served by a pool of SGSNs.

Routing Area

A RA, either a GSM RA or a WCDMA Systems RA, is an area which is served by a given SGSN. One SGSN can handle several RAs. An MS may move between RAs with the SGSN area without roaming to a new SGSN. The size of an RA can range from a part of a city to an entire province, or even a small country. An RA consists of one or more cells.

Cell

A cell, either a GSM cell or a WCDMA Systems cell, is the smallest geographical unit in the GPRS service area. It is the basic unit of a mobile cellular network and is covered by one RBS. GSM cells are covered by a GSM RBS and WCDMA Systems cells are covered by a WCDMA Systems RBS.

The size of a GSM cell is static, but can vary from cell to cell. When expecting many users per unit area, a geographically small cell is preferable, when expecting few users, a geographically large cell is preferable. A cell change in GSM can be visible to the packet-switched part of the GSM network.

 GPRS Main Procedures:

  • Mobility Management
  • Attach procedure
  • Detach procedure
  •  PDP activation
  •  Data transfer
  •  PDP deactivation

GPRS Mobility Management :

Before a mobile station (MS) can send or receive data, it must attach to a Serving GPRS Support Node (SGSN)

During the attachment procedure aTLLI and a P_TMSI are assigned to the MS.After attaching one or more PDPs can be negotiatiated with the SGSN.

There are 3 MM states related to a GPRS subscriber and each statedescribes the level of functionality and information allocated

  •  IDLE state

The MS is not yet attached to to the GPRS mobility management.

  •  READY state

The MS is attached to GMM and is known in the accuracy of the cell. Each cell isassociated with the routing area(RA).The MS can receive and send data for all relevant service types

  •  STANDBY state

If the ready timer expires, the MS will move to the STANDBY state. In the standby state, the  subscriber is still attached to the GMM and is known in the accuracy of the RA. While in standby state, if the subscriber wants to send or receive data, a PDP context must be activated in advance

If the standby timer expires,the MM contexts in both the MS and SGSN independently return to the idle state and may be deleted

PDP (Packet Data Protocol)

  • Activating a PDP Context for PacketRouting and Transfer

Before data can be sent or received, a PDP context (a data address) must be activated (created for the MS) A GPRS subscribtion contains several PDP addresses and an individual PDP context is maintained in the MS, SGSN and GGSN for every PDP address.It is possible to inquire/set the following parameters in PDP

1)Requested QoS (peak bit rate, mean bit rate, delay requirements, reliability level expected.)

2)Data compression or no data compression

3)Wheteher or not to use TCP/IP header compression  PDP address and type requested

  • Each PDP context can be either active or inactive and 3 PDP context functions   are available as discussed before i.e-activate, deactivate, modify

The MS is responsible for activationa and deactivation

GGSN is responsible for activation (for incoming packets) and deactivation

SGSN is responsible for modification

A MS in standby or ready state can initiate activation or deactivation at anytime to activate the PDP context in the MS, the SGSN or the GGSN


About Author:

I am Hardik Chauhan, working in Nokia Siemens Networks as Sr Engineer. Future of telecom industry in India is data ,examples are endless,so many network providers like Vodafone, Airtel, Idea etc are already providing 3G services and in near future 4G will be also available.I would like to share so  me knowledge regarding GPRS (General Packet Radio Service) which is used by almost every person now a days .

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