The 7750 SR, 7450 ESS, and 7950 XRS support the MS-PW path trace mode of operation for VCCV trace, as per pseudowire switching, but using FEC129 AII type 2. As in the case of vccv-ping, the SAII:TAII used in the VCCV echo request message sent from the T-PE or S-PE from which the VCCV trace command is executed is specified by the user or derived from the context of the MS-PW. The use of spoke-sdp-fec-id in vccv-trace is only applicable at T-PE nodes because it is not configured for a specified MS-PW at S-PE nodes.