Will a X2-10GB-LR work with a loopback

[timchampion]

Hi, I'm trying to find out for sure if a X2-10GB-LR will come up when looped. If a loop is valid for this optic module is an attenuator required or any additional interface level configuration.....?

Thanks in advance,

Tim

[Michael Dooley]

Tim,

I did a search on www.cisco.com and found this page:

http://www.cisco.com/en/US/partner/prod/collateral/modules/ps5455/ps6574/product_data_sheet0900aecd801f92aa_ps5251_Products_Data_Sheet.html

Basically, the X2-10G-LR transmits an optical level between +0.5dbm and -8.2dbm and the receiver can handle an optical level between +0.5dbm and -14.4dbm.  So, it should work fine with a loop and no optical attenuator.

As to whether it will "come up"...  the X210GB-LR will work looped, but I do not know if the port of whatever it is plugged into will come up.  That depends on the equipment.

Mike Dooley

Cisco Optical TAC

[timchampion]

Thanks for your reply Mike. So an attenuator is only needed when the Tx Power is potentially greater than the Rx power?

Regarding your comment on the link "coming up", are you suggesting that the optic may see the link as up but that this may not be passed up the stack to the Ethernet level?

[Tom Randstrom]

Tim,

Correct. You only need an attenuator when the expected receive optical power is above the maximum value for the receiver (+0.5dB in this case).  Having too much power at the receiver is just as bad as having too little; it can cause bit errors on the link.

Some optical interfaces designed for long haul networks require attenuators for short links or loopbacks, because their output power is higher than the receiver's target input power (max).

[Michael Dooley]

Tim,

Tom provided the answer to the need for an attenuator.  On the link "coming up" you may see the link come up, but the protocol is not up.  Again, it depends on the port... ethernet.. pos... whatever it is.

Mike

[timchampion]

Thanks all for your replies - I now understand why attenuators are required! Will do some reading on the 10G ethernet standard to see if a loopback will work.