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:

• Authentication Handling
• Data Compression and Ciphering
• 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

  • If it is active the GGSN forwards the data packets to the serving SGSN
  • 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 it self 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.

GPRS:

General Packet Radio Services (GPRS) is a best-effort packet-switching protocol for wireless and cellular network communication services. It is considered best effort because all packets are given the same priority and the delivery of packets isn't guaranteed.

The 3rd Generation Partnership Project (3GPP) standardized GPRS in early 1998, but commercial cellular networks did not widely adopt the technology until 2000. It was the first technology successfully deployed in 2G mobile phone systems.

What made GPRS technology different from other cellular wireless technologies, like Global System for Mobile Communications (GSM), available at the time was the use of packet-switched data instead of the traditional circuit-switched data. When a cellphone was on circuit-switched mode, the circuit was permanently switched on to a specific user. By contrast, packet-switched data transfers occurred in bursts during short peaks, followed by breaks.

This approach was a more efficient use of available capacity because, by splitting data into packets and tags, GPRS shared overall capacity among multiple users. This was possible because everyone wasn't online at the same time often. The destination address became available when inserted into the packet, which enabled packets from multiple sources to transmit through a single link.

GPRS performance classes:

The industry classifies GPRS mobile networks by the number of slots they can accommodate. Multislot classes determine the speed of uplink and downlink voice and data transfer range from 1 to 45. As levels of operation and capability vary, a good indicator of a device's service ability is its GPRS performance class. GPRS has three classes based on an ability to connect GSM and GPRS services.

The three classifications are as follows:

Class A. Cellular phones that connect to both GSM and GPRS services concurrently.

Class B. Can connect to both GSM and GPRS services but not simultaneously.

Class C. Use either GPRS or GSM services, but the user must switch between the two manually.

GPRS data speeds depend on the number of time slots available for use in either direction. These slots send and receive data, uplink or downlink. GPRS also uses channel encoding processes called cyclic code and convolutional code, the latter of which is a type of error-correcting code.