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? Thanks
On Sat, 19 Oct 2013, 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?
If this is using Cisco 10GBASE-LR optics, then padding in this instance should not be necessary. However, if SR optics (again, assuming these are Cisco devices), would be a better fit for the distance, using an OM3 or OM4 multimode jumper. The reason I asked about the vendor is because things like SR and LR can mean different things to different vendors. jms
Hi Chris, I'm with an optics vendor, Luma optics. All our optics are field programmable to work in any intended network environment. Regarding your question, its unnecessary to pad a 10km LR, even with such a short reach ( 20m) . If it were an ER or ZR, it would be a different story. Good luck with you project. Regards, Eric Litvin LumaOptics.net 650 996 7270 Sent from my iPhone
On Oct 19, 2013, at 7:33 PM, Chris Costa <ccosta92630@gmail.com> 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?
Thanks
On Sat, 19 Oct 2013, Chris Costa wrote:
median RX range to avoid potential receiver burnout over time, or just leave it un-padded?
By "padding", you mean "insert attenuator"? I have run networks with thousands of 10km optical links (1GBASE-LX, 10GBASE-LR) and none of them have used attenuators for these kinds of links, not even with 1m cable. The discussion has been had here before, some attenuate, some don't. There is no consensus. -- Mikael Abrahamsson email: swmike@swm.pp.se
Subject: Pad 1310nm cross-connects? Date: Sat, Oct 19, 2013 at 07:33:19PM -0700 Quoting Chris Costa (ccosta92630@gmail.com):
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?
LR usually needs padding in that scenario, IMHO. This also applies to MMR interconnects or other "premises" / "campus" situations. 5 or 10dB depending on patching quality -- sometimes up to 15. The value is best determined by measuring the signal. Then compare the measurement with the line card / SFP datasheet and determine the amount of padding necessary. As you write, the damage from overload is gradual, so simply trusting "it works" is quite bad for longevity reasons. Not all line cards and / or optical modules report the input signal level, so a good meter sometimes is necessary. Get a good level meter, and a reasonably good light source for testing and calibration purposes. I'm happy with our purchase of SMLP4-4[0] from AFL Noyes. -- Måns Nilsson primary/secondary/besserwisser/machina MN-1334-RIPE +46 705 989668 Pardon me, but do you know what it means to be TRULY ONE with your BOOTH! [0] http://www.aflglobal.com/Products/Test-and-Inspection/Loss-Test-sets/SMLP4-4...
Subject: Re: Pad 1310nm cross-connects? Date: Sun, Oct 20, 2013 at 07:21:42AM +0200 Quoting Måns Nilsson (mansaxel@besserwisser.org):
Subject: Pad 1310nm cross-connects? Date: Sat, Oct 19, 2013 at 07:33:19PM -0700 Quoting Chris Costa (ccosta92630@gmail.com):
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?
LR usually needs padding in that scenario, IMHO. This also
My apologies. I was thinking not of 10km / 20km class optics but the 80-100km stuff. There, padding is quite necessary in short-range setups. For 10/20km stuff, I, too, have run lots of 2m patch cords directly between linecards without harm. -- Måns Nilsson primary/secondary/besserwisser/machina MN-1334-RIPE +46 705 989668 One FISHWICH coming up!! Courtesy conversions: (km->miles, km-> miles, metres/100 -> feet) 10/1.6 6.25000000000000000000 80/1.6 50.00000000000000000000 200/(2.54*12) 6.56167979002624671916
It's a pretty normal situation. even with a 1-2m jumper I see light levels that are well below the maximum rx levels for 10km optics. e.g. the max might be .5 and the actual readings are -1.4 - -2.7. our WDM terminals sit in the the adjacent racks to the pop routers so they're all like that. ER/ZR is another matter. On Oct 19, 2013, at 7:33 PM, Chris Costa <ccosta92630@gmail.com> 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?
Thanks
On Sun, 20 Oct 2013, joel jaeggli wrote:
It's a pretty normal situation. even with a 1-2m jumper I see light levels that are well below the maximum rx levels for 10km optics. e.g. the max might be .5 and the actual readings are -1.4 - -2.7. our WDM terminals sit in the the adjacent racks to the pop routers so they're all like that.
ER/ZR is another matter.
Yes, ER/ZR must be attenuated unless the run is sufficiently long. We have a link that's a bit too long for LR, but we still had to attenuate because the ER optics were reporting excessively high receive levels. jms
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/refer... And similar for 1000baseLX, the similar technology for GigE: http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/refer... 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 - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/
participants (8)
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Chris Costa -
Eric Litvin -
joel jaeggli -
Justin M. Streiner -
Leo Bicknell -
Mikael Abrahamsson -
Måns Nilsson -
Sam Roche