Correct Answer - Option 2 : Abis
The Base Station Subsystem is responsible for managing the radio network, and it is controlled by an MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a considerably large geographical area consisting of many cells (a cell refers to an area covered by one or more frequency resources). The BSS consists of the following elements:
- BSC Base Station Controller
- BTS Base Transceiver Station
- TRAU Transcoder and Rate Adaptation Unit (often referred to as TC (Transcoder))
The Abis interface consists of the protocols spoken between the BSC (Base Station Controller) and BTS (Base Transceiver Station).
The Abis interface allows control of the radio equipment and radio frequency allocation in the BTS.
Hence option (2) is the correct answer.