08.513GPPBase Station Controller - Base Tranceiver Station (BSC-BTS) Interface General AspectsTS
The interface is defined to be at the terrestrial link of a remote BTS connected to the BSC.
The BSC to BTS interface is specified by a set of characteristics, including:
a) physical and electrical parameters;
b) channel structures;
c) signalling transfer procedures;
d) configuration and control procedures;
e) operation and maintenance information support.
The definition of the BSC to BTS/TRX interface follows a layered approach similar to the ISDN. Layer 3 is for the most part based on Technical Specification 3GPP TS 08.08 with additional procedures for control of radio resources. Layer 2 is based on the LAPD protocol. Layer 1 is either digital (at a rate 2048 kbit/sec with a frame structure of 32 x 64 kbit/sec time slots or at a rate of 64 kbit/sec.) or analogue with the data being passed by the use of modems (this latter case is a national option).
In the case that the transcoder is positioned outside the BTS, the overall one way propagation delay between the Point Of Interconnection to PSTN/ISDN and the MS is limited to 1.5 ms (approximately 300 km). With the transcoder in the BTS, the limit is 6.5 ms (approximately 1300 km). These limits may be subject to increase resulting from savings made in the overall network. See also Technical Specification 3GPP TS 03.50.