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
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
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.
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.
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
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.
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:
And similar for 1000baseLX, the similar technology for GigE:
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.