Cisco Systems 8540 CSR, 8510 CSR appendix About the POS OC-12c Uplink Interface, Pos

Chapter 4 Configuring Interfaces

About the POS OC-12c Uplink Interface

Because SONET/SDH (Synchronous Digital Hierarchy) is by definition a point-to-point circuit, PPP is well suited for use over SONET links. The octet stream is mapped into the SONET/SDH synchronous payload envelope (SPE) in accordance with RFC 2615, “PPP over SONET/SDH,” and RFC 2615, “PPP in HDLC-like Framing.” Octet boundaries are aligned with the SPE octet boundaries, and the PPP frames are located by row within the SPE payload. Because frames are variable in length, the frames can cross SPE boundaries. Using this scheme, multiprotocol data can be encapsulated and transported directly into SONET frames without relying on ATM to provide Layer 2 capability (for example, in IP over ATM over SONET).

About the POS OC-12c Uplink Interface

POS technology is ideally suited for networks that are built for providing Internet or IP data. It provides superior bandwidth utilization and efficiency over other transport methods. For expensive WAN links, POS can provide as much as 25 to 30 percent higher throughput than ATM-based networks.

Transporting frames directly into the SONET/SDH payload eliminates the overhead required in ATM cell header, IP over ATM encapsulation, and segmentation and reassembly (SAR) functionality.

Figure 4-4shows a typical application of the POS OC-12c uplink interface module in an enterprise setting. Here the enterprise backbone is comprised of POS links among Catalyst 8540 campus switch routers in each building.

Figure 4-4 POS for Enterprise Backbone Connectivity

OC-12c POS	OC-12c POS
	POS
OC-12c POS	OC-12c POS

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	Layer 3 Switching Software Feature and Configuration Guide
78-6235-04, Cisco IOS Release 12.0(10)W5(18)		4-13