In a message written on Sat, Oct 19, 2013 at 07:33:19PM -0700, Chris Costa wrote: > What are the opinions/views on attenuating short, 1310nm LR cross-connects. > Assume < 20m cable length and utilizing the same vendor optics on each > side of the link. Considering the LR transmit spec doesn't exceed the > receiver's high threshold value do you pad the receiver closer to the > median RX range to avoid potential receiver burnout over time, or just > leave it un-padded?
With any optics, you need to go to the specifications. I assume here you mean 10GbaseLR, although I will point out that "LR" is ambiguous as there is also for instance OC192-LR. I'm going to pick on Juniper specs, just because they were the easiest to find with Google: http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/specifications/transceiver-m-mx-t-series-10-gigabit-optical-specifications.html And similar for 1000baseLX, the similar technology for GigE: http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/specifications/transceiver-m-mx-t-series-1000base-optical-specifications.html Note that for both 10GbaseLR and 1000baseLX the transmitter power range is entirely inside the allowed receiver range. They were designed this way on purpose, to never need a pad. An in-spec optic can never over drive the receiver, even with zero loss. Answering your question, I would never pad them. Compare with for instance a 10Gbase-ER or 1000baseEX, 40km over single mode optics. In both cases an in-spec can exceed a receiver. 10Gbase-ER can transmit up to +4.0dBm, while the receiver needs -1.0dBm or below. When connecting them "back to back" a 5dB attenuator is required to keep the receiver in-spec. For any real connections (over a fiber path more trivial than a jumper) a light meter should be used, the value checked, and an attenuator that places the circuit 1-2dB inside of the safe zone of the receiver should be used. -- Leo Bicknell - bickn...@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/
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