GPRS is usually attempts to reuse the existing GSM network
elements as much as possible. There are new entities called GPRS
supports nodes (GSN) which are responsible for delivery and routing
of data packets between mobile stations and external packets
networks. There are two types of GSNs,
- Serving GPRS Support Node (SGNS)
- Gateway GPRS Support Node (GGNS)
There is new database called GPRS register which is located with
HLR. It stores routing information’s and maps the IMSI to a PDN address. Thus, GPRS Reference Architecture is shown as:
SGSN: It is at the same hierarchical level as the MSC. Whatever the
MSC does for voice, SGSN does for Packet Data. The tasks of SGSN
include packet switching, routing and transfer, mobility management
and location management, logical link management and
authentication and charging functions
SGSN processes the registration of new mobile subscriber and keeps
a record of the location inside a given service area.
GGSN: It acts as an interface between GPRS backbone network and
the external packet data networks. GGSN’s function is similar to that
of a router in a LAN. It maintains the routing information that is
necessary to tunnel the protocol data units to the SGSNs.
GPRS Network enhancements: Some existing GSM network
elements must also be enhanced in order to support packet data. The
BSS system needs enhancements to recognize and send packet data.
This includes BTS upgrade to allow transportation of user data to the
SGSN. Also the BTS needs to be upgraded to support packet data
transmission between the BTS and the MS. HLR and VLR also
require enhancements so the queries from GSNs may handled. MS
also needs enhancements
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