GPRS operations with its architecture:

• The GPRS is an enhancement over the GSM and adds some nodes in the network to provide the packet switched services. These network nodes are called GSNs (GPRS Support Nodes) and are responsible for the routing and delivery of the data packets to and form the MS and external packet data networks (PDN).
• A General Packet Radio Service (GPRS) network is composed of the following network nodes:

Serving GPRS Support Node (SGSN):

• The SGSN is the node that is serving the MS; it is responsible for GMM. It delivers packets to the MSs and communicates with the HLR to obtain the GPRS subscriber profile within its area of responsibility.
• The main functions of SGSN are packet routing and transfer, mobile attach and detach procedure (Mobility Management (MM), location management, assigning channels and time slots (Logical Link Management (LLM)), authentication and charging for calls.
• It stores the location information of the user (like the current location, current VLR) and user profile (like IMSI addresses used in packet data networks) of registered users in its location register.
• It manages the registration of the new mobile subscribers in order to keep a record of their LA for routing purposes. The SGSN can be connected to one or several BSSs.

Gateway GPRS Support Node (GGSN):

• The GGSN provides interworking with external packet data networks (PDNs). It may be linked to one or several data networks. It is connected with SGSNs via an IP-based GPRS backbone network.
• The gateway GPRS support node (GGSN) acts as interface between the GPRS backbone and the external packet data network (PDN).
• It converts the GPRS packet coming from the SGSN into proper packet data protocol (PDP) format (i.e. X.25 or IP) before sending to the outside data network.
• Similarly it converts the external PDP addresses to the GSM address of the destination user. It sends these packets to proper SGSN.
• For this purpose the GGSN stores the current SGSN address of the user and his profile in its location register.
• The GGSN also performs the authentication and charging functions. In general there may be a many to many relationship between the SGSN and GGSN.
• However a service provider may have only one GGSN and few SGSNs due to cost constraints.
• The GGSN is a router that forwards incoming packets from the external PDN to the SGSN of the addressed MS.
• It also forwards outgoing packets to the external PDN. The PDN is the external fixed data network to which is connected the GPRS network. An example of a PDN is the Internet network.

Home Location Register (HLR):

• The HLR is a database that contains, among other things, packet domain subscription data and routing information.

Mobile switching center/visitor location register (MSC/VLR):

• The MSC coordinates the setting up of calls to and from GSM users and manages GSM mobility.
• The MSC is not directly involved in the GPRS network. It forwards circuit-switched paging for the GPRS-attached MS to the SGSN when the Gs interface is present.

Base Station Subsystem (BSS):

• The BSS ensures the radio connection between the mobile and the network. It is responsible for radio access management.
• The BSS is composed of two elements: the BTS and the BSC. The BTS integrates all the radio transmission and radio reception boards. The BSC is responsible for the management of the radio channels.
• The BSC has switching capabilities that are used for circuit-switched calls and can also be used for GPRS traffic.

Equipment Identity Register (EIR): The EIR is a database that contains terminal identities.