IEEE C37.94-2017 pdf download

IEEE C37.94-2017 pdf download.IEEE Standard for N times 64 kbps Optical Fiber Interfaces between Teleprotection and Multiplexer Equipment.
6. Clock timing
6.1 General
The optical signal comprises a binary (on-off) modulation with a 2048 kbps bit stream with the timing requirements listed in 6.2, 6.3, and 6.4.
6.2 Frequency
The frequency shall he 2048 khps +100 ppm.
Each multiplexer end unit shall not use the signal from the teleprotection equipment for synchronization.
Each teleprotection equipment end unit shall use the signal from the multiplexer unit for synchronization:
upon LOS, the unit shall free-run with the above tolerance.
Each multiplexer end unit shall be able to detect the overhead ‘Yellow” bit correctly, even when the multiplexer end unit has lost synchronization (due to loss of optical input).
For clarification, the above requires that
a) The multiplexer unit normally receives data from the teleprotection equipment, at the same frequency as the multiplexer unit’s outgoing data, but during the failure of the outgoing fiber, the multiplexer unit must accept incoming data up to +100 ppm off frequency (detect framing, the overhead bits, and the data bits). it is acknowledged that being asynchronous to the multiplexer will cause bits to be lost, or filled (as in an asynchronous 64 kbps JTU-T G.703 interface), but this is considered preferable to squelch ing the data.
b) The teleprotectioii equipment shall be able to receive signals with up to ± 100 ppm frequency tolerance on its optical input, and use this for the frequency of its outgoing signal to the multiplexer. If its input is bad, or lost, the teleprotection equipment shall use an internal reference with ± 100 ppm tolerance.
For the teleprotection equipment output. the jitter shall be within ±100 ns (± 0.2 UI). (This allows its clock recovery circuit to add ±50 ns to the jitter it receives.)
The multiplexer unit’s receiver shall tolerate a jitter of± 100 ns.
For clarification, the above requires that if the data are observed on an oscilloscope triggered on either rising or falling transitions, the next transition should be at a minimum of438 ns for the multiplexer unit output and a minimum of388 ns to 438 ns for the teleprotection equipment output (depending on thejitter on its input data).
6.4 Wander
The multiplexer unit shall be able to operate with any roundirip delay with a maximum wander of ±250 ns (±0.5 UI) peak-to-peak.
7. Optical output levels
7.1 Level (multimode)
The mean optical power into 50 .im multimode fiber shall be > —23.0 dBrn and <—11.0 dBrn. The mean optical power into 62.5 im multimode fiber shall be > —19.0 dBrn and <—11.0 dBrn. The data format is light bON for logic b1t bits. The optical power for logic “0” bits shall be < 10% of the level for logic “1” bits. This corresponds to an extinction ratio of> 10 dB.
7.2 Level (single-mode)
The mean optical power into single-mode fiber shall be> —19.0 dBm and <—11.0 dBm. The data format is light “ON” for logic ‘1” bits. The optical power for logic “0” bits shall be < 10% of the level for logic “1” bits. This corresponds to an extinction ratio of> 10 dB.
8. Wavelengths
8.1 Wavelength (multimode)
The center emission wavelength shall be 830±40 nm.
8.2 Wavelength (single-mode)
The center emission wavelength shall be 1310 * 40 nm.
Annex C
(informative)
Harmonization with other standards
C.1 Harmonization with IEC standards and ITU recommendations
C.tI Introduction
As far as could be determined by the working group, there was no suitable IEC standard, or work toward such a standard; however, there were some ITU recommendations that have been considered.
Ci.2 ITU-T G.704 recommendation for frame structure
ITU-T G.704 section 2.3 [B4j specifies a recommended frame structure for 2048 kbps interfaces.
Additional comments regarding this ITU-T recommendation are as follows:
This document is compliant with ITU-T G.704 [B4j, specifically including the use of bit #3 in the non- frame-alignment section of the header for RD1 or ‘4Yellow” bit.
The “CRC-4” and “Synchronization Status Messages” options of ITU-T G.704 [B4] are not mandatory and are not supported in this standard.
C.1 .3 ITU-T G.706 recommendation for loss of frame (LOF)
ITU-T G.706 section 4. 1.1 [B5] recommends “Frame alignment will be assumed to have been lost when three consecutive incorrect frame alignment signals have been received,” and it recommends a variety of algorithms for recovery.
Additional comments regarding this ITU-T recommendation are as follows:
This IEEE standard uses only the one term “LOS” to denote Loss of Signal, whether due to a low or no received power level, or due to a bad data pattern caused by some electronic failure.
LOS is declared upon receiving two or more errors in eight consecutive framing patterns, and cleared upon receiving eight consecutive correct framing patterns.
These algorithms are simpler to implement, and clearer to understand, than those for LOF in ITU-T G.706 [B5].