<P> The Packet-Over-SONET Model 50 (POSIP-OC3-50) provides a single 155.520-Mbps Packet OC-3 network interface for Cisco 7000 series and 7500 series routers. 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 specification is primarily concerned with the use of the PPP encapsulation over SONET/SDH links, and since SONET/SDH is by definition a point-to-point circuit, this product is well-suited for use over these links. </P>