Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 18

The architecture of a GPRS network and its elements for packet data services only is shown in Figure 2.2. As shown in this figure, a GPRS network uses the GSM BSS and NSS. However, the BSS provides the GPRS IP packet data services through a separate hardware unit as well as a software component which is known as the Packet Control Unit (PCU).

A PCU performs all the packet services‐related functions independently but in association with the BSC. Also, two new network elements on the NSS end are SGSN and GSSN. They communicate with each other over an IP transport network. GGSN has the interface to the external PDN over an IP transport network.

Functionality wise, an SGSN in a PS domain performs similar functions to an MSC in the CS domain core network. SGSN keeps track of the current locations of MSs and performs the PS domain control, i.e. mobility management and session management, and user data transfer functions. An SGSN can be interconnected with an MSC to deliver CS domain‐related paging services to an MS in case it is engaged in a PS session. The GGSN serves as the gateway for a GPRS network to an external IP network. Apart from this, a GGSN allocates IP addresses to a registered MS. Both the SGSN and the GGSN use the IP transport network.