Initiation And Transmission Of Slm Requests; Reception Of Slms And Transmission Of Slrs - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Initiation and Transmission of SLM Requests

Reception of SLMs and Transmission of SLRs

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A MEP maintains the following local counters for each test ID and for each peer MEP
being monitored in a maintenance entity for which loss measurements are to be
performed:
TxFCl—Number of synthetic frames transmitted toward the peer MEP for a test ID. A
source MEP increments this number for successive transmission of synthetic frames
with ETH-SLM request information while a destination or receiving MEP increments
this value for successive transmission of synthetic frames with the SLR information.
RxFCl—Number of synthetic frames received from the peer MEP for a test ID. A source
MEP increments this number for successive reception of synthetic frames with SLR
information while a destination or receiving MEP increments it for successive reception
of synthetic frames with ETH-SLM request information.
The following sections describe the phases of processing of SLM PDUs to determine
synthetic frame loss:
A MEP periodically transmits an SLM request with the OpCode field set as 55. The MEP
generates a unique Test ID for the session, adds the source MEP ID, and initializes the
local counters for the session before SLM initiation. For each SLM PDU transmitted for
the session (test ID), the local counter TxFCl is sent in the packet.
No synchronization is required of the test ID value between initiating and responding
MEPs because the test ID is configured at the initiating MEP, and the responding MEP
uses the test ID it receives from the initiating MEP. Because ETH-SLM is a sampling
technique, it is less precise than counting the service frames. Also, the accuracy of
measurement depends on the number of SLM frames used or the period for transmitting
SLM frames.
After the destination MEP receives a valid SLM frame from the source MEP, an SLR frame
is generated and transmitted to the requesting or source MEP. The SLR frame is valid if
the MEG level and the destination MAC address match the receiving MEP's MAC address.
All the fields in the SLM PDUs are copied from the SLM request except for the following
fields:
The source MAC address is copied to the destination MAC address and the source
address contains the MEP's MAC address.
The value of the OpCode field is changed from SLM to SLR (54).
The responder MEP ID is populated with the MEP's MEP ID.
TxFCb is saved with the value of the local counter RxFCl at the time of SLR frame
transmission.
An SLR frame is generated every time an SLM frame is received; therefore, RxFCl in
the responder is equal to the number of SLM frames received and also equal to the
number of SLR frames sent. At the responder or receiving MEP, RxFCl equals TxFCl.
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