5???). Although originally
designed to transport IP traffic, MPLS has developed into one of the key technologies
in delivering Carrier Ethernet services.
Technology Description
We will now go on to give an overview of MPLS, and of the pseudowire and VPLS technologies
that extend MPLS to offer Ethernet services, before examining how Ethernet
over MPLS meets the MEF-defined Carrier Ethernet attributes.
Connectionless and Connection-Orientated Forwarding
There are two classes of packet-switched network technologies??”connectionless and
connection-orientated. Ethernet MAC switching is an example of connectionless forwarding,
whereas ATM switching is an example of connection-orientated forwarding.
In a connectionless network, each router (or switch) decides independently how to
forward each packet. Of course, in order for packets to be forwarded successfully across
the network, routers must make consistent forwarding decisions. A router??™s forwarding
decision is reached by running a forwarding algorithm using two pieces of input data:
the packet header and a ???forwarding table??? held by the router. Thus, for consistency in
forwarding decisions, the forwarding algorithms and forwarding tables of the routers
must be consistent.
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