A switch is a packet-forwarding device, such as a bridge (layer 2 switch) or a router (layer 3 switch), that determines the destination of individual data packets (such as Ethernet frames) and selectively forwards them across a packet switched network (such as an IP or MPLS packet switched network) according to the best route to their destination. The best route is associated with one of a number of ports on the packet-forwarding device, which are the device's external interface to the network.
In a network that supports pseudo wire emulation, the ports on the packet-forwarding device may include both real ports and pseudo wire ports. Pseudo wires are used to emulate native wire-line services, such as Ethernet, over a packet switched network (see, Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture, RFC 3985, March 2005). In general, a real port refers to a physical port on the packet-forwarding device through which packets may be transmitted, such as an Ethernet port. A pseudo wire port refers to a virtual port associated with one or more pseudo wires through which packets may be transmitted.
Packets transmitted to and from a packet-forwarding device through a pseudo wire port generally travel through a tunnel across the packet-switched network; the packet-forwarding device itself may be unaware whether the packets transmitted through its ports are transmitted using real ports or pseudo wire ports.
In today's packet-forwarding devices, much of the packet forwarding is performed in the switch fabric. The switch fabric is a hardware component of the packet-forwarding device, and thus provides high-speed forwarding performance. The packets transmitted through the pseudo wire ports, however, typically require additional pseudo wire processing to provide proper forwarding, not all of which is capable of being performed in the switch fabric of a typical packet forwarding device. For example, the pseudo wire traffic may require special echo kill or load balancing processing. As a result, the additional pseudo wire processing is typically performed in software rather than in the switch fabric, which can impair the efficiency of the forwarding function of the packet forwarding device, especially when handling large volumes of packets transmitted through pseudo wire ports.