This Recommendation gives functional characteristics of interfaces associated with:

network nodes, in particular, synchronous digital multiplex equipment and digital exchanges in IDNs for telephony and ISDNs; and

PCM multiplexing equipment.

Clause 2 deals with basic frame structures, including details of frame length, frame alignment signals, Cyclic Redundancy Check (CRC) procedures and other basic information.

Clauses 3 to 6 contain more specific information about how certain channels at 64 kbit/s and at other bit rates are accommodated within the basic frame structures described in clause 2.