scope:

This standard provides the physical layer (Layer 1) specifications for DS3 User-Network Interfaces (UNIs) that are used to transport asynchronous transfer mode (ATM) cells in the DS3 payload. The term User- Network Interface (UNI) is used in this standard to refer to both the Network Interface (NI) and interfaces within the Customer Installation (CI).

DS3-ATM interfaces include, but are not limited to, DS3 access to a Broadband - Integrated Services Digital Network (B-ISDN). For information concerning the four B-ISDN reference points (UB, TB, SB, and SSB), see T1.646-1995.

This standard addresses synchronization, line code, framing format, ATM mapping, and connectors associated with the DS3-ATM interface. Specifications for processing the header error check (HEC) and for maintenance and performance monitoring of a DS3 signal that transports ATM cells are also provided, by reference, in this document.

All requirements are applicable at all UNIs unless specifically identified as being applicable to the NI or the Ia and Ib interfaces. T1.646-1995 defines interface points Ia and Ib as physical locations designating the boundaries between functional groupings. Interface point Ia is adjacent to the B-TE, B-NT2, and BNT1 on their network side; interface point Ib is adjacent to the B-NT2 and B-NT1 on their user side (refer to T1.646-1995 for a graphical representation).

Unless otherwise specified, the descriptions and requirements herein refer to the direct mapping of ATM cell streams into DS3 payloads. An older format for mapping ATM into DS3, the physical layer convergence protocol (PLCP), is now obsolete but is described in Annex A for historical purposes.

This standard is a revision of the portions of T1.646-1995 that refer, in the generic sense, to the transport of ATM cells in the DS3 payload. Portions of T1.646-1995 that relate specifically to the use of DS3 transport for B-ISDN applications will remain in the revision of T1.646-1995. The provisions of this standard are intended to be consistent with applicable requirements concerning safety and environmental conditions.