scope:

This standard describes the Tandem Connection Overhead layer for SONET. The SONET standard is specified in American National Standard for Telecommunications T1.105-2001, Basic description including multiplex structure, rates, and formats. The Tandem Connection layer is an optional layer that falls between the Line and Path layers defined in T1.105-2001. This overhead layer deals with the reliable transport of Path layer payload and its overhead across a network. The use of Tandem Connection is application specific and at the discretion of the carrier. It is expected that the principal applications for Tandem Connection will be in the inter-office network, and that Tandem Connections will generally not be used in applications such as the subscriber access network.

This standard is also documented in ITU-T Recommendation G.707 where it is referred to as " VC-4- Xc/VC-4/VC-3 Tandem Connection Monitoring protocol: option 1." ITU-T Recommendation G.707 also contains two additional methods of Tandem Connection Monitoring.

- VC-4-Xc/VC-4/VC-3 Tandem Connection Monitoring protocol: option 2. This method differs mainly from the method of this standard in that it monitors a single VC-4- Xc/VC-4/VC-3, whereas the method of this standard monitors bundles of VC-4- Xc/VC-4/VC-3.

- VC-2/VC-1 Tandem Connection Monitoring protocol. This method provides Tandem Connection Monitoring over virtual tributaries.