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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Emulated<br />

Ethernet<br />

MUX<br />

MPLS<br />

Figure A-5 Encapsulation of Ethernet over MPLS<br />

When emulating Ethernet over MPLS networks:<br />

► The Label Distribution Protocol (LDP) sets up a pseudo wire (as opposed to a<br />

real Ethernet cable wire, or a Ethernet switch) on MPLS.<br />

► The Ethernet pseudo wire carries the Ethernet/802.3 protocol data units<br />

(PDUs) over MPLS.<br />

► The pseudo wire emulation consists of the destination address, source<br />

address, length/type, MAC client data, <strong>and</strong> padding extracted from a MAC<br />

frame as a concatenated octet sequence in their original order.<br />

► Usually, only point-to-point Ethernet connections are emulated as the<br />

broadcast operation in a real Ethernet.<br />

► The emulation can provide multiplexing <strong>and</strong> demultiplexing at the consumer<br />

edge routers so that aggregrated traffic is between provider edge MPLS<br />

routers.<br />

► An Ethernet PW operates in one of two modes, raw mode or tagged mode:<br />

– In tagged mode, each frame must contain at least one 802.1Q Virtual LAN<br />

tag, <strong>and</strong> the tag value is meaningful to the NSPs at the two pseudo wire<br />

termination points.<br />

– On a raw mode PW, a frame may contain an 802.1Q VLAN tag, but if it<br />

does, the tag is not meaningful to the NSPs, <strong>and</strong> passes transparently<br />

through them.<br />

► In addition to providing a bridge of Ethernet frames over MPLS, the pseudo<br />

wire methods can provide frame delivery in sequence as well as other QoS<br />

controls.<br />

We expect that over time other protocols such as ATM will be emulated as well.<br />

940 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

Ethernet<br />

service<br />

Packet<br />

Tunnnel Tunnnel<br />

Physical<br />

Emulated<br />

Ethernet<br />

MUX<br />

MPLS

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