Hi Jack
Port Based Psuedowire is one of the various options available for configuring a psuedowire between two endpoints.
In a Port-Based Psuedowire the ethernet frame is transparently encapsulated into an MPLS Packet and transported across the backbone to the other end where the MPLS Packet is decapsualted and the ethernet frame is sent out via the egress..This helps in providing a pure point-to-point link between the two remote endpoints as if a physical wire was used..
Other options available such as VLAN Based psuedowire where the SP reads the VLAN Tag information and removes the same before encapsulating the frame into an MPLS Packet. This means that the CEs can use different VLANs locally signficant till their respective PEs at each end and still communicate transparently..
Hope this provides some insight to your query...
You can try reading a very useful book" MPLS Configuration on CIsco IOS Softwares" which provides a very comprehensive insight into the various MPLS concepts.
Regards
Varma
