The dynamic MS-PW model also adds support for signalling the bandwidth required
by a pseudowire. In the SS-PW case, this is unnecessary because each PE can select
an LSP with the required bandwidth to meet the requirements of the pseudowire and
can adjust the available bandwidth of the LSP appropriately. Likewise, in the statically
configured MS-PW case, each S-PE can select the appropriate LSP for its attached
pseudowire segments. However, in the dynamic MS-PW case, it is useful to have a
mechanism by which the source T-PE can indicate the bandwidth required to each S-PE
in the path. Consideration has also been given to enabling the source T-PE to select an
explicit path to the target T-PE (i.e., a set of S-PEs to traverse).
The dynamic MS-PW architecture represents the final stage in the evolution of
pseudowires from being simply an edge-to-edge multiplexing mechanism for carrying
circuits over LSPs to being a fully dynamic system capable of scaling to the largest
networks and supporting inter-provider operation. This system consists of the set of
interconnected T-PEs and S-PEs and uses Type 2 AIIs as its addressing mechanism,
MP-BGP as its routing protocol (and, in fact, work has also commenced on using IGPs
to flood Layer 2 reachability), and targeted LDP as its signalling protocol.
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