Differences in dispersion compensation between 40G coherent boards and 40G non-coherent boards

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40G non-coherent boards use the TDC technology and the dispersion tolerance is 800 ps/nm. 40G coherent boards use the DSP technology and the dispersion tolerance reaches 60,000 ps/nm. A network deploying non-coherent boards must use DCMs for dispersion compensation. A network that uses only coherent boards does not need to use DCMs.

Other related questions:
Whether coherent 40G boards require dispersion compensation, and dispersion tolerance of the LSQ board
No dispersion compensation is required for coherent 40G boards, and the dispersion tolerance of the LSQ board (non-coherent) is ±800 ps/nm.

Methods for determining the over-compensation or under-compensation according to the dispersion compensation of the 40G board, and conditions for dispersion search
Query the WDM performance events. If the compensation value is negative, the line is under-compensated; if the compensation value is positive, the line is over-compensated.

Method used to distinguish coherent boards from non-coherent boards
40G boards have both coherent and non-coherent boards. All 100G boards are coherent boards. The following lists the coherent and non-coherent 40G boards, and 100G boards that are applicable to the OSN 8800: 40G coherent boards: TN15LSXL, TN55NS3, TN56NS3, TN54HUNS3 40G non-coherent boards: TN11LSXL, TN12LSXL, TN11LSXLR, TN12LSXLR, TN11LSQ, TN11LSQR 100G coherent boards: TN12LSC, TN14LSC, TN11LTX, TN12LTX, TN54NS4, TN56NS4

Differences in commissioning a non-coherent system and a coherent system
The main difference in commissioning a non-coherent system and a coherent system is the position of the transmit-end EVOA. In a coherent system, the transmit-end EVOA is always located after the OA board. In a non-coherent system, the transmit-end EVOA is located after the OA board only in the non-standard fiber access mode.

Reason why a coherent system uses fewer OA boards than a non-coherent system
OA boards are used to compensate for insertion loss. Only one OA board is required in case that Gmax (maximum gain) �?Fiber loss + DCM loss; otherwise, two OA boards are required. The coherent system does not require DCMs, and a single OA board can compensate for larger link loss. When the link loss is within the permitted range, the coherent and non-coherent systems require the same number of OA boards. When the fiber loss is out of the permitted range, the coherent system, however, requires fewer OA boards. For example, in a system with a 60 km span, 18 dB fiber loss, and 5 dB DCM loss: The gain required by a coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 18 dB + 0 dB (no DCM) = 18 dB < Gmax. Therefore, one OA board (OAU101) is required. The gain required by a non-coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 18 dB + 5 dB = 23 dB < Gmax. Therefore, one OA board (OAU101) is required. In a system with a 100 km span, 28 dB fiber loss, and 9 dB DCM loss: The gain required by a coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 28 dB + 0 dB (no DCM) = 28 dB < Gmax. Therefore, one OA board (OAU101) is required. The gain required by a non-coherent system is calculated as follows: Gain = Fiber loss + DCM loss = 28 dB + 9 dB = 37 dB > Gmax (36 dB for an EDFA board). Therefore, two OA boards (OAU101 and OBU101) are required.

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