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

Mon Aug 8 10:20:13 EDT 2011

2011/8/7 Martin T <m4rtntns at gmail.com>

> 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?

Not at all.  As I said each type of transceiver will have a different
rating.  So a 1310nm single mode sfp with a max distance of 10km will be
much more powerful than an 850nm multimode sfp with a max distance of 500m.
 It takes more power to push light 10km than it takes to push it 500m.  Also
the multimode optics are led based and the single mode ones are laser, so
they aren't even the same type of light.

In addition, what is a "Maximum Receiver
> Sensitivity"?
>

This one I'm not 100% sure about.  It sounds like the lowest the rx can go
before the switches considers the interface down, but that's just a guess.

>
>
> 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..
>

The devices don't communicate signal strength so the transmitting device has
no way of knowing what the other device is receiving if anything at all.  In
general the path is either good or bad.  The signal will vary from one
second to the next but not because of any attempt at boosting the signal.

> 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....
> >> >
> >> > _______________________________________________
> >> > juniper-nsp mailing list juniper-nsp at puck.nether.net
> >> > https://puck.nether.net/mailman/listinfo/juniper-nsp
> >> >
> >>
> >>
> >> _______________________________________________
> >> juniper-nsp mailing list juniper-nsp at puck.nether.net
> >> https://puck.nether.net/mailman/listinfo/juniper-nsp
> >>
> >>
> > _______________________________________________
> > juniper-nsp mailing list juniper-nsp at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/juniper-nsp
> >
>
>