This TS defines the Logical Link Control (LLC) layer protocol to be used for packet data transfer between the Mobile Station (MS) and Serving GPRS Support Node (SGSN).
It defines the frame structure, elements of procedure, format of fields, and procedures for the proper operation of the logical link control layer. It is based on ideas contained in IS-130, ISO 3309, ISO 4335, and ISO 7809 (HDLC of ISO), as well ITU-T Q.920 and Q.921 (LAPD). The concepts, the overview description of LLC layer functions and procedures, and the relationship with other Technical Specifications are described in general terms in TS 03.60
LLC spans from the Mobile Station (MS) to the Serving GPRS Support Node (SGSN). LLC is intended for use with both acknowledged and unacknowledged data transfer.
The frame formats defined for LLC are based on those defined for LAPD and RLP. However, there are important differences between LLC and other protocols, in particular with regard to frame delimitation methods and transparency mechanisms. These differences are necessary for independence from the radio path.