Pseudowire ( sometimes spelled as "pseudo wire" or abbreviated as PW) is a mechanism for emulating various networking or telecommunications services across packet-switched networks that use Ethernet, IP, or MPLS. Services emulated can include T1 leased line, frame relay, Ethernet, ATM, TDM, or SONET/SDH. As defined in RFC 3985 ("Pseudo Wire Emulation Edge-to-Edge [PWE3] Architecture") a pseudowire delivers the bare minimum of functionality necessary to emulate a wire with some required degree of fidelity for some specific service definition.
Required functions for PWs include the following:
- Encapsulating service-specific bit streams, cells, or protocol data units (PDUs) that appear at some ingress port, then ferrying them across some IP path or through an MPLS tunnel.
- Occasionally managing order and timing of incoming PW traffic so as to properly emulate a service with the necessary fidelity (TDM and ATM are good examples where timing issues are very important).
Seen from the perspective of customer edge equipment (CE), a PW appears to be an unshared link or a circuit for some designated service. PWs provide a relatively straightforward mechanism to implement arbitrary services across packet-switched networks, and to achieve interoperability among arbitrary sets of equipment from multiple vendors.