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PoS (Packet over SONET)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

A major goal of service providers is to transport IP packets over underlying physical networks with as little overhead as possible. In the Ethernet LAN environment, IP packets go into Ethernet frames, a relatively straightforward and efficient mechanism. In the WAN environment, a typical scenario is to put IP packets in ATM packets and then into SONET frames, as shown on the left in Figure P-6 (see book).

This topic continues in "The Encyclopedia of Networking and Telecommunications."

PoS can be viewed as three layers, and each layer is defined by the following Internet RFCs:

  • Top layer: IP encapsulation into PPP    See RFC 1661 (The Point-to-Point Protocol, July 1994)

  • Mid layer: Framing of PPP with HDLC    See RFC 1662 (PPP in HDLC-like Framing, July 1994)

  • Bottom layer: Mapping into SONET    See RFC 2615 (PPP over SONET/SDH, June 1999)

PPP provides a standard method for transporting multiprotocol datagrams over point-to-point links. RFC 2615 is the primary document that describes the use of PPP over SONET and SDH circuits. All the physical layer requirements, framing, and configuration details are outlined in the RFC.

MPLS extends the functionality of PoS by supporting ATM-like virtual circuits and QoS capabilities in a PoS environment. See "MPLS (Multiprotocol Label Switching)."

RFC 2823 (PPP over Simple Data Link [SDL] Using SONET/SDH with ATM-like framing, May 2000) describes a new encapsulation for PPP called SDL (Simple Data Link). SDL provides a very-low-overhead alternative to HDLC-like encapsulation, and can also be used on SONET/SDH links. The IETF Point-to-Point Protocol Extensions (pppext) Working Group has a full list of PPP drafts and RFCs.

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