ETH-CFM (802.1ag and Y.1731)
Page 80 7705 SAR OS Services Guide
Priority Mapping (802.1ag and Y.1731)
Operators often run OAM tests over a single, specific forwarding class (FC). For example,
an operator might be mapping OAM traffic to FC2 (AF – Assured Forwarding) and, in order
to examine the delay, jitter, or loss qualities of the OAM traffic, would need to run OAM
tests using FC2. To provide operators with the ability to control which FC the OAM packets
will follow, the priority priority command is included in several OAM test commands.
When the 7705 SAR generates an Ethernet OAM frame, it uses the priority as per the user’s
configuration of the priority keyword and then sends the frame through the datapath.
Thus, the OAM frame follows the entire datapath and receives the same treatment as any
other user frame before it is switched over the port.
For example, a CCM frame generated by a SAP Up MEP with a priority value of 7 will
receive the following treatment.
• First, the CCM frame is classified as per the access ingress and QoS policy settings.
For example, the CCM frame can be mapped to the BE forwarding class if the
assigned QoS policy has its priority 7 mapped to BE.
• Then, the OAM packet is mapped to the associated queue (the queue hosting the BE
forwarding class) and follows ingress scheduling like any other datapath frame.
• Next, the CCM frame is switched through the fabric and reclassified to the network
egress queues, as per the assigned QoS policy classifiers.
• Finally, the CCM frame is scheduled again, as per the queue type and profile state of
the queue.
This implementation replicates the user experience since the OAM packet follows the same
path as the data packets.
Priority Mapping for SAP Up MEPs
For Up MEPs on a SAP, priority mapping operates as described in the following list, which
indicates how the messages or replies generated on ingress have their FC and VLAN tag
priority set.
The resulting frames (CCM, LMM, DMM, DM1, LMR, or DMR) are inserted in the access
ingress datapath and are processed in the same way as any other frame. That is, they are
classified based on the sap-ingress policy.
• Continuity Check messages (CCMs) generated on ingress are based on the setting of
the ccm-ltm-prio command for the MEP (that is, the VLAN tag priority is set
according to the ccm-ltm-prio command for the MEP).
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