BTSM
GSM 08.58 http://www.etsi.fr
BTSM is the Base Station Controller to Base Transceiver Station (BSC - BTS) interface protocol (the A-bis interface). BTSM allows sending messages between the Base Station Controller and the Base Transceiver Station. Protocol messages consist of a series of information elements. For each message there are mandatory information elements and optional information elements. BTSM messages are transmitted on the A-bis interface using the I format of LAPD, except for the Measurement Result message which is sent in UI format.
Message discriminator 1-octet field used in all messages to discriminate between Transparent and Non-Transparent messages and also between Radio Link Layer Management, Dedicated Channel Management, Common Channel Management and TRX Management messages.
Message type Uniquely identifies the function of the message being sent. It is a single octet field.
Read more about this topic: Cellular Data Communication Protocol