Single-Ended Frame-Loss Measurements

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.

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). The following figure shows the transmission of LMM and LMR for frame-loss measurement.
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Two-Way Frame-Loss Measurement
../Graphics/EX_oam_0003_FrameLoss.svg
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.

Far-End Frame Loss = (TxFCf[tc] – TxFCf[tp]) – (RxFCf[tc] – RxFCf[tp])

Near-End Frame Loss = (TxFCb[tc] – TxFCb[tp]) – (RxFCl[tc] – RxFCl[tp])