The Packet-Over-SONET specification is primarily concerned with the use of the PPP encapsulation over SONET/SDH links. Since SONET/SDH is by definition a point-to-point circuit, PPP is well suited for use over these links. Point-to-Point Protocol (PPP) was designed as a standard method of communicating over point- to-point links. The Synchronous Optical Network (SONET) is an octet-synchronous multiplex scheme that defines a family of standard rates and formats. The basic rate for Packet-Over-SONET is that of STS-3c/STM-1, which is 155.520 Mbps.The POSIP-OC3-50 provides a single 155.520-Mbps, Packet OC-3 network interface for Cisco 7000 series and 7500 series routers. For the POSIP-OC3-50 to operate properly in the Cisco 7000 series routers, the 7000 Series Route Switch Processor (RSP7000) and 7000 Series Chassis Interface (RSP7000CI) must be installed.