03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS
To support efficient radio interface usage in GPRS, the MS classmark is handled differently for SGSN-based services than for MSC-based services. In particular, the classmark is sent in MM messages to the network and stored in the network as long as the MS is GPRS-attached, avoiding redundant classmark retransmissions over the radio interface. This is sometimes called the "idle-mode classmark" principle.
In order to allow introduction of new radio access technologies in the future, the MS classmark is split into two distinct and independent information elements, the radio access classmark, and the SGSN classmark.
6.11.1 Radio Access Classmark
The radio access classmark contains the radio capabilities of the MS (e.g., multislot capability, power class), and more generally all the information that should be known by the BSS in order to handle radio resources for that MS.
The radio access classmark is a container for a multiplicity of radio access technology-dependent information, i.e., within the radio access classmark there are independent sub-fields for various technologies such as GSM 900, GSM 1800, Satellite, UMTS, etc. The coding shall allow a BSS to extract only the sub-fields relevant to it without interpreting the other sub-fields. This ensures that the radio classmark does not need to be interpreted by the NSS, and the full radio classmark is always sent by the MS to the SGSN, and thereafter provided to the BSS irrespective of the actual BSS capabilities.
The SGSN shall provide the radio access classmark as an information element on the Gb interface. It is the responsibility of the SGSN to provide the BSS with the most recent classmark received from the MS. The classmark information element can be included in a downlink transfer request, or be sent in a specific message that updates the radio classmark information in the BSS. The BSS may at any time request the radio classmark for a given MS to be transmitted from the SGSN to the BSS.
A specific optimisation allows the BSS to receive a reduced radio access classmark at initial access directly from the MS. This enables the BSS not to wait for the full radio access classmark to be provided by the SGSN, and is therefore quicker for the initial MS-originated transmission. The reduced classmark can be carried is several RR messages depending on the access method, e.g., in the initial random access message, or in the first uplink radio block. Details are provided in GSM 04.08 and GSM 04.60.
6.11.2 SGSN Classmark
The SGSN classmark contains non radio-related capabilities, e.g., the ciphering capability. The SGSN stores the SGSN classmark which is used both locally by the SGSN and for transfer to the new SGSN at all types of inter SGSN RA update.