4 Logical configuration of the Gb-interface

08.183GPPBase Station System (BSS) - Serving GPRS Support Node (SGSN)BSS GPRS ProtocolGeneral Packet Radio Service (GPRS)Release 1999TS

4.1 High-level characteristics of the Gb-interface

In contrast to the A-interface, where a single user has the sole use of a dedicated physical resource throughout the lifetime of a call irrespective of information flow, the Gb-interface allows many users to be multiplexed over a common physical resource.

GPRS signalling and user data may be sent on the same physical resources.

Access rates per user may vary from zero data to the maximum possible bandwidth (e.g. the available bit rate of an E1).

4.2 Position of BSSGP within the protocol stack on the Gb-interface

Across the Gb-interface the following peer protocols have been identified: the Base Station Subsystem GPRS Protocol (BSSGP) and the underlying network service (NS). The NS shall transport BSSGP PDUs between a BSS and an SGSN (refer to 3GPP TS 08.16 [16]).

Figure 4.1: BSSGP’s position within the Gb-interface protocol stack

NOTE: The Relay function provides buffering and parameter mapping between the RLC/MAC and the BSSGP. For example, on the uplink the RLC/MAC shall provide a TLLI. The Relay function shall then make it available to BSSGP. For a definition of the RLC/MAC function refer to 3GPP TS 03.64 [10].

The primary functions of the BSSGP include:

– in the downlink, the provision by an SGSN to a BSS of radio related information used by the RLC/MAC function;

– in the uplink, the provision by a BSS to an SGSN of radio related information derived from the RLC/MAC function; and

– the provision of functionality to enable two physically distinct nodes, an SGSN and a BSS, to operate node management control functions.

The present doument describes the service model, service primitives, procedures and PDU formats of the BSSGP.