An NQA Pseudowire Emulation Edge-to-Edge (PWE3) ping test instance checks the reachability of a pseudo wire (PW) over a Multiprotocol Label Switching (MPLS) network. The PWE3 ping test process is shown in Figure 1.
A local device (PE1) selects a specified PW to send an MPLS Echo Request message to a remote device (PE2). After the remote device receives the message, it returns an MPLS Echo Reply message carrying the local device interface address to the local device.
After the local device receives the MPLS Echo Reply message, it forwards data along the PW.
The local device calculates the difference between the time the MPLS Echo Request message was sent and the time the MPLS Echo Reply packet was received. The length of time reflects PW connectivity.