This chapter presents several Layer-2 protocols. These protocols are used to encapsulate Layer-2 protocol data units (PDUs) for transmitting datagrams in the network. The chapter presents several examples of these encapsulation protocols, including Martini, Layer-2 Transport, and Pseudowire Emulation Edge-to-Edge.


Draft-Martini encapsulation [1] describes methods for encapsulating the Layer-2 PDUs such as Frame Relay, Asynchronous Transfer Mode (ATM), and Ethernet across a Multiprotocol Label Switching (MPLS) network.

Martini drafts contributed to the Internet Engineering Task Force’s (IETF’s) Pseudo Wire Emulation Edge-to-Edge (PWE3) working group by Luca Martini of Cisco Systems (formerly employed by Level 3 Communications) and a number of other authors. These drafts define a method to transport a Layer-2 protocol across an MPLS network. The Martini-trans series defines the transport mechanism using the Label Distribution Protocol (LDP). The Martini-encaps series of drafts define how specific Layer-2 protocols are encapsulated prior to being carried in the MPLS network. Provision is made for the synchronous optical networking (SONET) and synchronous digital hierarchy (SDH), Ethernet, ATM and frame relay. This protocol has been superseded by the PWE3 working group specifications described in RFC 4447 [2].

8.1.1 Functionality

In an MPLS network, it is possible to use control protocols such as those specified ...

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