The pseudowire label contains enough information for the egress
PE device to identify the pseudowire and handle the Ethernet frame appropriately. In
between the ingress and egress PEs lies a ???tunnel?????”a way to get from one PE to the
other without looking at either the original Ethernet frame or the pseudowire label.
In most cases, the tunnel is an MPLS label switched path (LSP); this is commonly
referred to as the ???Martini??? encapsulation, named after Luca Martini, the primary
author of the original IETF submissions [16, 17]. In cases where the pseudowire traverses
a non-IP network, many of the benefits of an MPLS-based tunnel are lost, and
the pseudowire may, therefore, use an attribute of the underlying network, such as
an ATM VC or SONET STS path, as the tunnel. This is the basis for ???Dry Martini???
encapsulation [18].
The marriage of MPLS, and in particular Ethernet-based PWE3, and SONET networks
provides some unique benefits:
?– MPLS provides a scalable packet-layer multiplexing technology for Ethernet.
Because MPLS labels have 20 bits, MPLS-enabled EoS networks can aggregate
and switch traffic from over one million PEs.
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