In order to provide Packet Data Service through GPRS, a new class of network nodes needs to be introduced as an upgrade to the existing GSM network. These network nodes are called as GSN (General Support Nodes).

There are two types of support nodes namely,

• The Serving GPRS support node (SGSN)
• The Gateway GPRS support node (GGSN)

The figure below shows the architecture of GPRS.

Functions of different blocks of GPRS are as follows:

SGSN:

• It is connected to the BSC and is the service access point (SAP) to the GPRS network for all the GPRS mobile users.
• It is similar to MSC used in GSM network and can be used as packet switched MSC.
• It Delivers packets to its mobile subscribers within its service area.
• SGSNs send queries to Home Location Registers to obtain profile data of GPRS subscribers and also performs registration and authentication process of new MS (mobile Subscribers)

Main Functions of SGSN Includes:

1. Authentication Handling
2. Data Compression and Ciphering

3. Mobility management

    

GGSN:

• It is connected to external packet data networks like internet

• When GGSN receives data addressed to a particular mobile data user, it checks if the call address is active

  1. If it is active the GGSN forwards the data packets to the serving SGSN
  2. If the called address is inactive, the received data packets are discarded.

• The mobile originated data packets are routed to the desired network by GGSN

• The GGSN tracks the mobile user in associated with the SGSN.
• GGSNs are used as interface to external IP networks such as public internet, GPRS service of other GPRS providers or intranet
• One or more GGSN may be available in GPRS network to support multiple SGSNs

• Other functions include network and subscriber screening and address mapping.

   

GPRS BSS:

• The Base Transceiver station (BTS) is a relay station which performs modulation and demodulation. A Software upgrade is required in the existing BTS to handle GPRS functionality
• The base Station Controller (BSC) also requires a software upgrade for GPRS mobility management and paging, and the installation of a new piece of hardware called Packet Control Unit (PCU)

• PCU directs the data traffic to the GPRS network and can be a separate hardware element associated with BSC; it also supports all the GPRS protocols for communication over the air interface.

   

DATABASES (VLR and HLR):

• HLR is home location register and VLR is visitor location register
• In GPRS MSC itself is used as VLR.
• HLR contains GPRS subscription data and routing information, and can be accessible from the SGSN; the HLR also maps each subscriber to one or more GGSNs.