IEEE Std C37.94-2017 pdf download – IEEE Standard for N times 64 kbps Optical Fiber Interfaces between Teleprotection and Multiplexer Equipment.
4.3 Channel data This 192-bit section comprises 96 data bits, with each data bit followed by its complement. The frst N × 8 data bits carry the N × 64 kbps data. The remaining 96 – (N × 8) data bits are set to 1. 4.4 Path frame alignment Note that this standard does not require multiplexer equipment to provide end-to-end frame alignments; i.e., there is no requirement that a frame’s frst data bit D1 at the source site appears as a frame’s frst data bit D1 at the destination site. 5. Communication failure scenarios 5.1 Loss of signal (LOS) It is important that a low-level (e.g., from a deteriorating optical fber) does not result in garbled data for more than a few milliseconds. The receiver shall declare LOS within 1 ms after receiving two or more errors in eight consecutive framing patterns. The receiver shall clear LOS upon receiving eight consecutive correct framing patterns.
5.2 Signal failure actions During LOS condition at its optical receive port, the teleprotection equipment shall — Change the “Yellow” bit in the transmitted optical output frames from “0” to “1”. During LOS condition at its optical receive port, the multiplexer shall — Replace the data bits over the higher order communications link with “All Ones,” which is commonly referred to as Alarm Indication Signal or AIS. — Change the “Yellow” bit in the transmitted optical output frames from “0” to “1”. During the loss of the higher order communications link, the multiplexer shall — Replace the data bits in the transmitted optical output frames with “All Ones.” 5.3 Path “Yellow” detection The receiver shall declare Path “Yellow” (Far-end in alarm) when BOTH of the following are true: — Three consecutive received frames have the “Yellow” bit = 1; and — The received signal is OK (no LOS). (Please note that the received data timing may be free-running, at ±100 ppm.) The receiver shall clear Path “Yellow” when ONE of the following is true: — Three consecutive received frames have the “Yellow” bit = 0; or — The received signal is bad (LOS). 5.4 Link failure response Figure 2, Figure 3, and Figure 4 illustrate the signals generated in the three possible link failure modes. Dashes indicate resultant signals. X indicates failure locations.