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Data Link Layer


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Data Link Layer

MPLS is able to work in an environment that uses any data link technology, connection-oriented and connectionless. MPLS also provides the potential for all traffic to be switched, but this depends on the granularity of label assignment, which again is flexible and depends on the approach used to identify traffic (discussed above). Labels may be assigned per address prefix (e.g., a destination network address prefix) or set of prefixes, and can also represent explicit routes. On a finer-grained level, labels can be defined per host route and also per user. At the lowest level, a label can represent a combined source and destination pair, and in the context of RSVP can also represent packets matching a particular filter specification.

Figure 12 - MPLS encoding for PPP/HDLC over SONET/SDH links

Figure 13 - MPLS encoding for ATM links

Currently, MPLS forwarding is defined for a range of link layer technologies, some of which are inherently label-switching (e.g., ATM and frame relay, FR) and others are not, such as packet over SONET/SDH-POS, Ethernet, and DPT. A number of encapsulation schemes are in Figure 12 and 13.





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