Single-ended frame-loss measurement facilitates on-demand OAM. MEPs
carry out frame-loss measurments by sending frames to peer MEPs with frame-loss
measurement request information and receiving frames with frame-loss measurement reply
information. This Y_1731 frame-loss measurement depends on VLAN statistics.
The PDU for single-ended frame-loss measurement requests is Loss
Measurement Message (LMM). The PDU for single-ended frame-loss measurement reply is Loss
Measurement Reply (LMR). Two-Way Frame-Loss Measurement shows the
transmission of LMM and LMR for frame-loss measurement.
Two-Way Frame-Loss Measurement
A MEP maintains two local counters for each peer MEP it is monitoring
for frame-loss:
TxFCl—in-profile data frames transmitted to the peer
MEP.
RxFCl—in-profile data frames received from the peer
MEP.
For an on-demand loss measurement, a MEP periodically transmits
LMM frames with TxFCf (value of the local TxFCl counter at the time
of LMM frame transmission). Upon receiving a valid LMM frame, a
MEP sends an LMR frame to the requesting MEP. (Valid LMM frames
have a valid MD level and a destination MAC address equal to the
receiving MEP's MAC address.)
An LMR frame contains the following values:
TxFCf—TxFCf value copied from the LMM frame.
RxFCf—RxFCl value when the LMM frame was received.
TxFCb—TxFCl value when the LMR frame was transmitted.
Upon receiving an LMR frame, a MEP uses the following values
to make near-end and far-end loss measurements:
Received LMR frame's TxFCf, RxFCf, and TxFCb values, and
local counter RxFCl value at the time this LMR frame was received. These values
are represented as TxFCf[tc], RxFCf[tc], TxFCb[tc], and RxFCl[tc]; where tc is
the time the current reply frame was received.
Previous LMR frame's TxFCf, RxFCf, and TxFCb values, and
local counter RxFCl value at the time the previous LMR frame was received. These
values are represented as TxFCf[tp], RxFCf[tp], TxFCb[tp], and RxFCl[tp],where
tp is the time the previous reply frame was received.
