[j-nsp] acceptable/good laser receive power in case of different interfaces

[evangellick@btinternet.com]

Receiver sensistivity applies in electrical interfaces as well as optical interfaces, typically this does effect SX devices, however it has been observed that you can overdrive the receive hardware on SX & TX interfaces. If the received electrical signal is to high to fit wiring the operating envelope of the receiver.
I understand in the case of optical, best common practice is to attenuate the signal to about the mid-point between maximum & minimum receiver sensitivities. In the case of electrical, resistive hybrid maybe used to attenuate by between 3dB & 6dB.
It is sometimes overlooked that to drive the receiver too high can be as bad as to send too low a signal.

I hope this helps

Sent from my HTC

----- Reply message -----
From: "Martin T" <m4rtntns at gmail.com>
Date: Sun, Aug 7, 2011 22:03
Subject: [j-nsp] acceptable/good laser receive power in case of	different interfaces
To: "Keegan Holley" <keegan.holley at sungard.com>
Cc: <juniper-nsp at puck.nether.net>


Lane,
while browsing the specifications of the optical modules listed in
this "Optical Interface Support—EX 3200 and EX 4200 Switches.pdf"
file:

http://www.juniper.net/techpubs/en_US/release-independent/junos/topics/reference/specifications/optical-interface-support-ex-series.pdf

...all the modules have minimum and maximum launch power which differ
from each other quite a lot. What does this mean? Shouldn't the launch
power be consistent? In addition, what is a "Maximum Receiver
Sensitivity"?


David, Keegan,
thank you for explanation!


In addition, there isn't some sort of connection between Rx power and
Tx power, is there? I mean for example in case the received signal is
low, the transmit signal of the SFP/XFP is increased automatically? As
far as I know and as Lane confirmed, the Tx signal should be always
consistent..


regards,
martin


2011/8/3 Keegan Holley <keegan.holley at sungard.com>:
> 2011/8/2 Joel Jaeggli <joelja at bogus.com>
>
>>
>> if these are sr multimode optics, the -15 number is low the -7 number is
>> marginal and everything else is decent.
>>
>> either the -15 one is quite long ( for sr) or needs to be
>> replugged/cleaned/reterminated
>>
>>
> Yea I agree.  The -15 is a bit low unless it's is at the end of a really
> long, low-quality fiber run I'd clean it and or replace the XFP.  It's
> blasting out at +1 and receiving much less, there could also be a mismatch
> of some sort.  There are lots of ways to mismatch optics and cabling and
> still get link.
>
>
>
>> On Aug 2, 2011, at 2:53 PM, chip wrote:
>>
>> > Depending on whose optics you're using there should be a data sheet
>> > that shows the acceptable Tx/Rx levels for each type available from
>> > your vendor.  I can't seem to locate a document for Juniper at the
>> > moment.  But I assume they shouldn't be that far off from Cisco stuff.
>> > For example, here's a data sheet for the XENPAK module:
>> >
>> >
>> http://www.cisco.com/en/US/prod/collateral/modules/ps2797/ps5138/product_data_sheet09186a008007cd00_ps5455_Products_Data_Sheet.html
>> >
>> > Check Table-2.
>> >
>> > As far as I know, an optic will output power within a specified range
>> > as according to what type it is, SR, LR, ER, ZR, etc...
>> >
>> > Hope that helps a bit.