scope:

This document describes the rates, formats, and transport overhead for interfaces referred to as SONET with a rate less than STS-1. Specifically, the additional transport overhead is defined that allows the transport of virtual tributary (VT) payloads at the VT15 and VT Group level across an interface. The SONET optical interface standard is defined in American National Standard for Telecommunications - Digital hierarchy - Optical interface rates and formats specifications (SONET), ANSI Tl .105-l 995, although the interfaces defined in this document are not restricted to either electrical or optical signals at the physical layer. Specific overhead functions and physical layer definitions are detailed in the normative references as noted in this document.