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Understanding MX Series Router Cloud CPE Ethernet Frame Delay Measurement Services

MX Series routers support both Layer 2 and Layer 3 jitter measurement. Layer 2 jitter measurement is provided through Ethernet frame delay measurements (referred to as ETH-DM in Ethernet specifications), which is part of Ethernet OAM. The ETH-DM session sends an Ethernet frame delay measurement protocol data unit (PDU) to the remote maintenance association end point (MEP) to measure one-way or two-way frame delays and delay variations. Layer 3 jitter measurement is provided through the real-time performance monitoring (RPM) service, which sends probes (such as ICMP-ping, UDP-ping) to a remote node to measure round-trip time (RTT) and jitter between the two nodes.

Note: For cCPE services, jitter is measured between the cCPE contexts.

Layer 2 Jitter Measurement Service — Ethernet Frame Delay Measurement

Ethernet frame delay measurement is introduced in ITU-T Y.1731 on top of the IEEE 802.1ag Ethernet connectivity fault management (CFM). CFM is an end-to-end per service instance (per VLAN) Ethernet Layer OAM protocol. Two peers of a CFM session do not need to be adjacent. CFM partitions the service network into various administrative domains. For example, operators, providers, and customers may be part of different administrative domains. Each administrative domain is mapped into one maintenance domain, which provides enough information to perform its own management, thus avoiding security breaches and making end-to-end monitoring possible. Each maintenance domain is associated with a maintenance domain level from 0 through 7. Level allocation is based on the network hierarchy, where the outermost domains are assigned a higher level than the innermost domains. Subscriber endpoints have the highest maintenance domain levels (from 5 through 7). In a CFM domain, each service instance is called a maintenance association. A maintenance association can be thought of as a full mesh of MEPs having similar characteristics. MEPs are active CFM entities generating and responding to CFM protocol messages. There is also a maintenance intermediate point (MIP), which is a CFM entity similar to the MEP, but more passive (MIPs respond only to CFM messages).

MEPs in the same maintenance association of the same maintenance domain exchange a continuity check message (CCM), which is a heartbeat message, to maintain the connectivity state with peers. Because CCM is a multicast Ethernet frame, it can pass through switches between two MEPs.

ETH-DM uses CFM as an infrastructure. It measures frame delay and frame delay variations (jitter) between two CFM MEPs, which must be in the same maintenance domain and maintenance association. You can start an ETH-DM in either one-way or two-way (round-trip) mode to gather frame delay statistics. You can also specify frame priority (802.1p) in an ETH-DM session.

Layer 3 Jitter Measurement — Real-Time Performance Monitoring

MX Series routers provide an RPM service that sends probes (such as ICMP-ping, UDP-ping) to a remote node (router) to measure RTT and jitter between the two nodes. The probe packet is timestamped when it exits and when it returns to the source. If the destination is another Juniper Networks router with the RPM service configured, the probe packet is timestamped when it is received at the destination and when the response exits the router. You can configure the probe’s DiffServ code point (DSCP) bits so that RPM can measure performance of traffic being managed by a specific CoS configuration.

Because RPM is performed between two PE routers, it is not specific to cCPE services and is not discussed here in detail. For more information about RPM, see Real-Time Performance Monitoring Services.