Full Description

The present document gives the principles on which the detailed interface specifications in the rest of the 3GPP TS 48.0xx series of Technical Specifications are based.

The set of fixed equipment accessed from the MSC through one particular instance of the interface will be later referred to as a Base Station System (BSS). A BSS ensures the coverage of n cells, where n can be 1 or more.

The function of a BSS may be further subdivided into a control function, performed by one Base Station Controller (BSC) and a transceiving function, performed by "n" Base Transceiver Station equipments (BTS), one for each cell. However, the study of such a split is outside the scope of the 48.0xx series of Technical Specifications, where the BSS will be considered as a whole.

The BSS-MSC interface defined in the 3GPP TS 48 series of Technical Specifications is designed to support a widerange of possible architectures on both sides. Characteristics like location of the transcoders/rate adaptation to the MSSor inside the BSS (either physically integrated into the transceivers or very near to the MSC) or the use of traffic orsignalling concentration at either side are left to the operators" choice. Annex A to the present document containsguidance information concerning the use of remote mobile switching units, which for the purposes of the presentdocument are considered as part of the MSC.

The BSS-MSC interface is commonly called 'A-Interface'. It is subdivided into the Control Plane (signalling) and theUser Plane (traffic). Throughout this document the term 'MSC' is used to reflect both planes of the Mobile CoreNetwork, although in some architecture the Mobile Core Network is split into MSC-Server (MSC-S) and MediaGateway (MGW).

Direct connection between two BSSs is not supported by this A-Interface.

This A-Interface may be based onTDM using 1 or more 2 048 kbit/s digital transmission system interfaces. Each 2 048 kbit/s interface provides31*64 kbit/s channels which can be used for traffic (User Plane) or signalling (Control Plane) as the operatorrequires, and/orIP supporting User Plane and/or Control Plane (SIGTRAN).The signalling is layered, terminology similar to thatin the OSI reference model is used in this series, however the layers referred to are not identical to theequivalently named layer in the OSI model.This A-Interface User Plane is defined at the boundary of the MSC andin case of TDM, it has a per channel bit rate of 64 kbit/s, but the net radio path traffic channel is at a rate of lessthan 16 kbit/s. A speech transcoder or data rate adapter function is thus needed for the rate conversion. Theinterface is designed such that the transcoding or rate adaptation function may be geographically situated ateither the MSC site or the BSS site, however the transcoder is considered to be part of the BSSin case of IP, it has a flexible channel bit rate, adapted to the payload size. The speech transcoding function canbe part of either the BSS or the Core Network or can be omitted (transcoding free operation), allowing e.g. foruse of both, PCM encoded speech and compressed speech, over the A-Interface. The data rate adapter function isalways located inside the BSS, using a 64kbit/s unrestricted digital interface (Clearmode) over IP.The A-Interface has been designed around the aims of 3GPP TS 48.001 allowing each component and the system as awhole to evolve.

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Edition: 14.0.0 Published: 04/01/2017 Number of Pages: 20File Size: 1 file , 100 KB