The Alternate-Marking Method, as described in [RFC 9341
], is applicable to a point-to-point path. The extension proposed in this document applies to the most general case of a multipoint-to-multipoint path and enables flexible and adaptive performance measurements in a managed network.
The Alternate-Marking methodology consists of splitting the packet flow into marking blocks, and the monitoring parameters are the packet counters and the timestamps for each marking period. In some applications of the Alternate-Marking Method, a lot of flows and nodes are to be monitored. Multipoint Alternate Marking aims to reduce these values and makes the performance monitoring more flexible in case a detailed analysis is not needed. For instance, by considering n measurement points and m monitored flows, the order of magnitude of the packet counters for each time interval is n*m*2 (1 per color). The number of measurement points and monitored flows may vary and depends on the portion of the network we are monitoring (core network, metro network, access network, etc.) and the granularity (for each service, each customer, etc.). So if both n and m are high values, the packet counters increase a lot, and Multipoint Alternate Marking offers a tool to control these parameters.
The approach presented in this document is applied only to unicast flows and not to multicast. Broadcast, Unknown Unicast, and Multicast (BUM) traffic is not considered here, because traffic replication is not covered by the Multipoint Alternate-Marking Method. Furthermore, it can be applicable to anycast flows, and Equal-Cost Multipath (ECMP) paths can also be easily monitored with this technique.
] applies to point-to-point unicast flows and BUM traffic. For BUM traffic, the basic method of [RFC 9341
] can be easily applied link by link; therefore, the multicast flow tree distribution can be split into separate unicast point-to-point links.
This document and its Clustered Alternate-Marking Method applies to multipoint-to-multipoint unicast flows, anycast, and ECMP flows. Therefore, the Alternate-Marking Method can be extended to any kind of multipoint-to-multipoint paths, and the network-clustering approach presented in this document is the formalization of how to implement this property and allow a flexible and optimized performance measurement support for network management in every situation.
Without network clustering, it is possible to apply Alternate Marking only for all the network or per single flow. Instead, with network clustering, it is possible to partition the network into clusters at different levels in order to provide the needed degree of detail. In some circumstances, it is possible to monitor a multipoint network by monitoring the network clusters, without examining in depth. In case of problems (packet loss is measured or the delay is too high), the filtering criteria could be enhanced in order to perform a detailed analysis by using a different combination of clusters up to a per-flow measurement as described in [RFC 9341
This approach fits very well with the Closed-Loop Network and Software-Defined Network (SDN) paradigm, where the SDN orchestrator and the SDN controllers are the brains of the network and can manage flow control to the switches and routers and, in the same way, can calibrate the performance measurements depending on the desired accuracy. An SDN controller application can orchestrate how accurately the network performance monitoring is set up by applying the Multipoint Alternate Marking as described in this document.
It is important to underline that, as an extension of [RFC 9341
], this is a methodology document, so the mechanism that can be used to transmit the counters and the timestamps is out of scope here.
This document assumes that the blocks are created according to a fixed timer as per [RFC 9341
]. Switching after a fixed number of packets is possible, but it is out of scope here.
Note that the fragmented packets' case can be managed with the Alternate-Marking methodology, and the same guidance provided in Section 6
of RFC 9341
also applies in the case of Multipoint Alternate Marking.