Throughput measurement is performed by sending frames to the far end at an increasing rate (up to wire speed) and measuring the percentage of frames received back. In general, the rate is dependent on frame size; the larger the frame size, the lower the rate.
The Y.1731 specification recommends the use of unicast ETH-LB and ETH-Test frames to measure throughput.
On the 7705 SAR, LBM processing and LBR generation is enhanced and occurs on the datapath, allowing the node to respond to loopback messages at wire speed and making in-service throughput tests possible. Therefore, if the 7705 SAR receives LBMs at up to wire speed, it can generate up to an equal number of LBRs. In order to process LBMs at wire speed, there must be either no TLVs or a single TLV (which is a data TLV) in the LBM frame. The End TLV field (0) must be present and the frame can be padded with data after the End TLV field in order to increase the size of the frame. The MAC address cannot be a multicast MAC address; it must be the MEP MAC destination address (DA).
Datapath processing of LBMs is supported with dot1ag and Y.1731 for the following MEPs:
SAP Up and Down MEPs
spoke SDP Up and Down MEPs
mesh SDP Up and Down MEPs (VPLS only)
For spoke or mesh SDP Up and Down MEPs, fastpath (datapath) LBM processing requires that both interfaces—the LBM receiver and the LBR transmitter—reside on the same adapter card. For example, if the 7705 SAR must perform a reroute operation and needs to move the next hop interface to another adapter card (that is, LBMs are received on one card and LBRs are transmitted on another), the fastpath processing of LBMs is terminated and LBM processing continues via the CSM.