Two-Way Active Measurement Protocol Light (TWAMP Light)

TWAMP Light is an optional model included in the TWAMP standard RFC 5357, A Two-Way Active Measurement Protocol (TWAMP). TWAMP Light uses the standard TWAMP packet format but provides a simpler approach to gathering ongoing IP delay and synthetic loss performance data for the base router and per-VPRN statistics. Full details are described in Appendix I of RFC 5357.

With TWAMP Light, the TWAMP client/server model is replaced with a session controller/responder model. The server, control-client and session-sender role is combined in one host called the controller, and the session-reflector role is in another host called the responder. In general terms, the session controller is the launch point for the TWAMP test packets and the responder reflects the packets.

TWAMP Light maintains the TWAMP test packet exchange but eliminates the TWAMP TCP control connection with local configurations; however, not all negotiated control parameters are replaced with local configurations. The DSCP value in an incoming TWAMP test packet is reflected back to the originator. The incoming TWAMP test packet is classified to a specific FC based on the ingress QoS policy and the dot1p in the reflected packet is determined by the FC to dot1p mapping in the egress QoS policy.

The reflector function is configured under the config>router>twamp-light command hierarchy for base router reflection, and under the config>service>vprn> twamp-light command hierarchy for per-VPRN reflection. The TWAMP Light reflector function is configured per context and must be activated before reflection can occur; the function is not enabled by default for any context. The reflector requires the operator to define the TWAMP Light UDP listening port that identifies the TWAMP Light protocol and to define the prefixes that the reflector will accept as valid sources for a TWAMP Light request.

If the source IP address in the TWAMP Light packet arriving on the responder does not match a configured IP address prefix, the packet is dropped. Multiple prefix entries may be configured per context on the responder. Configured prefixes can be modified without shutting down the reflector function. An inactivity timeout under the config>oam-test>twamp>twamp-light command hierarchy defines the amount of time the reflector will keep the individual reflector sessions active in the absence of test packets.

TWAMP uses a single packet to gather both delay and loss metrics. This means there is special consideration over those approaches that use a specific tool per metric type.

TWAMP Light is supported for deployments that use IPv4 or IPv6 addressing, which may each have their own hardware requirements. All IP addressing must be unicast. IPv6 addresses cannot be reserved or link local addresses. Multiple test sessions may be configured between the same source and destination IP endpoints. The 4-tuple lookup (source IP, destination IP, source UDP, destination UDP provides a unique index for each test point.