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

[Joel Jaeggli]

On Aug 7, 2011, at 2:03 PM, Martin T wrote:

> 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"?

you're looking at emitters with rather different properties... a 1000sx or 100fx multimode gbic is an 850nm emitter (that's visible wavelength red) and probably uses an led and is meant for 50 or 62.5micron multimode, a 850nm or 1310/1550 nm qsfp+ gbic uses a vertical cavity emitting laser.

 Maximum reciever sensitivity I think would normally be characterized as dynamic range. acceptable input power on the rx side would be between -1 and -25dBm on 1000baselr if it's higher than that, you may need to attenuate it.. for example if you put the 10Gb's ER gbics back-to-back you'll need an attenuator, to keep them from blinding each other.

> 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?

remember that the TX and RX are on different fibers which (you hope) have similar properties.

> 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.
>>>> 
>>>> 
>>>> On Tue, Aug 2, 2011 at 5:26 PM, Martin T <m4rtntns at gmail.com> wrote:
>>>>> What is the acceptable Rx power in case of SFP/XFP? For example, here
>>>>> are XFP Tx and Rx signals from six FXP's:
>>>>> 
>>>>> 1:
>>>>> Laser output power                        :  1.2920 mW / 1.11 dBm
>>>>> Laser rx power                            :  0.0285 mW / -15.45 dBm
>>>>> 
>>>>> 2:
>>>>> Laser output power                        :  0.6420 mW / -1.92 dBm
>>>>> Laser rx power                            :  0.3054 mW / -5.15 dBm
>>>>> 
>>>>> 3:
>>>>> Laser output power                        :  0.4230 mW / -3.74 dBm
>>>>> Laser rx power                            :  0.5092 mW / -2.93 dBm
>>>>> 
>>>>> 4:
>>>>> Laser output power                        :  0.4180 mW / -3.79 dBm
>>>>> Laser rx power                            :  0.4208 mW / -3.76 dBm
>>>>> 
>>>>> 5:
>>>>> Laser output power                        :  1.0920 mW / 0.38 dBm
>>>>> Laser rx power                            :  0.1801 mW / -7.44 dBm
>>>>> 
>>>>> 6:
>>>>> Laser output power                        :  0.7680 mW / -1.15 dBm
>>>>> Laser rx power                            :  0.3337 mW / -4.77 dBm
>>>>> 
>>>>> 
>>>>> Is there some sort of pattern? It looks like if the Rx signal is
>>>>> lower, the Tx is higher? And what can one consider a decent Rx laser
>>>>> power level?
>>>>> 
>>>>> 
>>>>> regards,
>>>>> martin
>>>>> _______________________________________________
>>>>> juniper-nsp mailing list juniper-nsp at puck.nether.net
>>>>> https://puck.nether.net/mailman/listinfo/juniper-nsp
>>>>> 
>>>> 
>>>> 
>>>> 
>>>> --
>>>> Just my $.02, your mileage may vary,  batteries not included, etc....
>>>> 
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>>> 
>>> 
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