Telecom Techniques Guide


Basic of GSM Um,Abis and A Interface

GSM (Um) Air Interface

  • This is the interface between the GSM mobile station and the GSM Base station.
  • The Air interface (RF Interface) uses the Time Division Multiple Access (TDMA) technique to transmit and receive traffic and signaling information between the GSM BTS and GSM Mobile Station.
  • The TDMA technique is used to divide each carrier into eight time slots. These time slots are then assigned to specific users, allowing up to eight conversations to be handled simultaneously by the same carrier (Actual Traffic is Vary based on Code Rate Which Article¬†Publish Separately).

GSM Abis Interface

  • The GSM A-bis interface is responsible for transmitting traffic and signaling information between the GSM BSC and the GSM BTS its First Actual Physical Connection for Call.
  • The GSM transmission protocol used for sending signaling information on the A-bis interface is Link Access Protocol on the D Channel (LAPD)

GSM A Interface

  • GSM A interface between the GSM BSC and the GSM MSC
  • The GSM A interface provides two distinct types of information, signaling and traffic, between the MSC and the BSC.
  • The speech is transcoded in the TRC and the SS7 (Signaling system) signaling is transparently connected through the TRC or on a separate link to the BSC.