As a main technology for setting up a metropolitan area network (MAN), virtual private LAN service (VPLS) has been widely applied globally. VPLS, however, is poor in terms of service management and monitoring. In this case, an optimized VPLS OAM mechanism is required.
On a VPLS network, the performance of PWs affects the entire network performance. For example, the connectivity of PWs determines whether traffic can be normally forwarded between users, and the forwarding performance of PWs determines whether the forwarding capacity of the network complies with the Service Level Agreement (SLA) signed with users. To monitor PWs on the VPLS network, VPLS PW ping and VPLS PW trace are developed for detecting the connectivity of PWs, collecting performance information about PWs, discovering packet forwarding paths along PWs, and locating faults on PWs.
VPLS PW ping or VPLS PW trace operations initiated through NQA commands are the same as ping or trace operations initiated through common command lines in principle, and additionally provide the scheduling and result collection mechanism and the threshold-exceeding alarm function.
VPLS PW ping and VPLS PW trace comply with standard protocols in implementing PW detection: MPLS echo packets that carry Forwarding Equivalence Class (FEC) fields are encapsulated in tunnel mode and labeled with the Router Alert option; the Router Alert function is enabled on the VPLS network. MPLS echo packets are transmitted between PEs to detect PWs and are not sent to CEs, which means that the NQA test instance can be configured only on PEs. If an NQA test instance is configured on a non-PE device, it cannot be started because there is no VSI used for establishing PWs on the non-PE device and as a result, the test result is "drop."