This is my first e-mail to the list and I hope it is not entirely
As a suggestion, could you please in the future not use a subject such as
"Re: NANOG Digest, Vol 47, Issue 56" for posts. It is MUCH better to
use a topical subject line
(see my suggestion above); that helps people who filter their mail
keep track of threads and topics.
Regards
Marshall
> inappropriate. We are attempting to use Juniper single-mode SFPs (LX
> variety) across multi-mode fiber. Standard listed distance is always
> for SFPs using the appropriate type of fiber. Does anyone out there
> know how much distance we are likely to get? Thanks for your help in
> advance.
Single mode just has a smaller core size for the smaller "beam" emitted by
laser vs. LED. it works although I've never done it outside of a lab (MM
is cheaper). As for the distance it theory that should come down to the
optics and your transmit power. Hopefully this is just a cable connecting
the router to a long line. I've never heard of a 10K MM fiber run since SX
optics can't shoot that far. You should be able to get through the 500m or
so that MM optics are rated for, but YMMV (errors, light levels, bounces,
etc etc)
Cisco gives specs for SFP LX over MM (they aren't that great at gig, and really suck at
10G; if you have 50u OM3/OM4 you can do much better at 10G).
See SFP/fiber/distance table at
http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html
We have run LX-over-MM (62.5) on short building runs as a band-aid until SM is
available, and trying to do all new building MM with 50u OM3/OM4. We do have some
dependence on 62.5u MM - used by our aging Simplex alarm system - which does
point-to-point looped token ring <*cough*> on the alarm side. I'm trying to get them to
confirm 50u will work point-to-point, but at some non-alarm-points there would be a
necessary 50-to-62.5 exchange taking place and I'm not certain how to accomplish that
(50->62.5 would likely have tolerable loss, but not 62.5->50).
(I would suspect similar results cross-vendor but YMMV)
Jeff
In a nutshell, don't do it if at all possible. This issue gets significantly
worse at 10G. If there's any way to get SMF in place for this link, do it.
In practice, you will likely get something less than the rated distance, particularly if the MM fiber in question is an older type, such as OM1. If you're using OM1, mode-conditioning jumpers at both ends are pretty much a must.
The problems with shooting an LX/LH beam over MMF are threefold:
1. Attenuation on some flavors of MMF can be significantly higher than an equivalent run of SMF.
2. Modal dispersion on MMF will scatter and distort the LX beam, likely resulting in link errors because the receiver can't recover the data correctly.
3. Shooting a 9 micron beam into a 50 (or worse, 62.5) micron core, and getting enough of the beam to reach the 9 micron target at the other end to result in a recoverable signal is problematic.
jms
inappropriate. We are attempting to use Juniper single-mode SFPs (LX
variety) across multi-mode fiber. Standard listed distance is always
for SFPs using the appropriate type of fiber. Does anyone out there
know how much distance we are likely to get? Thanks for your help in
advance.Single mode just has a smaller core size for the smaller "beam" emitted
by
laser vs. LED. it works although I've never done it outside of a lab (MM
is cheaper). As for the distance it theory that should come down to the
optics and your transmit power. Hopefully this is just a cable connecting
the router to a long line. I've never heard of a 10K MM fiber run since
SX
optics can't shoot that far. You should be able to get through the 500m
or
so that MM optics are rated for, but YMMV (errors, light levels, bounces,
etc etc)In a nutshell, don't do it if at all possible. This issue gets
significantly
worse at 10G. If there's any way to get SMF in place for this link, do it.+1 probably should have added that. I guess I just assumed.
In practice, you will likely get something less than the rated distance,
particularly if the MM fiber in question is an older type, such as OM1. If
you're using OM1, mode-conditioning jumpers at both ends are pretty much a
must.The problems with shooting an LX/LH beam over MMF are threefold:
1. Attenuation on some flavors of MMF can be significantly higher than an
equivalent run of SMF.
+1 Assumed again..
2. Modal dispersion on MMF will scatter and distort the LX beam, likely
resulting in link errors because the receiver can't recover the data
correctly.
Not that I'm advocating this, but it's fine over short distances. I did
this for a few lab routers where I wasn't concerned with link quality, but
I was able to fill a 10G pipe with no errors/retransmit over about 10M.
3. Shooting a 9 micron beam into a 50 (or worse, 62.5) micron core, and
getting enough of the beam to reach the 9 micron target at the other end to
result in a recoverable signal is problematic.
Again for short distances it's doable. I agree not to even try over 62.5
though.
inappropriate. We are attempting to use Juniper single-mode SFPs (LX
variety) across multi-mode fiber. Standard listed distance is always
for SFPs using the appropriate type of fiber. Does anyone out there
know how much distance we are likely to get? Thanks for your help in
advance.Single mode just has a smaller core size for the smaller "beam"
emitted by
laser vs. LED. it works although I've never done it outside of a lab
(MM
is cheaper). As for the distance it theory that should come down to the
optics and your transmit power. Hopefully this is just a cable
connecting
the router to a long line. I've never heard of a 10K MM fiber run
since SX
optics can't shoot that far. You should be able to get through the
500m or
so that MM optics are rated for, but YMMV (errors, light levels,
bounces,
etc etc)In a nutshell, don't do it if at all possible. This issue gets
significantly
worse at 10G. If there's any way to get SMF in place for this link,
do it.In practice, you will likely get something less than the rated
distance, particularly if the MM fiber in question is an older type,
such as OM1. If you're using OM1, mode-conditioning jumpers at both
ends are pretty much a must.
I sense confusion in the above.
- LX drivers on MM fibre can work with Mode-Conditioning patch leads and
can give you significant distance wins, particularly if you're using
legacy OM1 Fibre.
- SX drivers on SM fibre is not something i've ever seen done, I can't
imagine why you'd do it - even if SX drivers are cheaper.
The problems with shooting an LX/LH beam over MMF are threefold:
1. Attenuation on some flavors of MMF can be significantly higher than
an equivalent run of SMF.
2. Modal dispersion on MMF will scatter and distort the LX beam,
likely resulting in link errors because the receiver can't recover the
data correctly.
3. Shooting a 9 micron beam into a 50 (or worse, 62.5) micron core,
and getting enough of the beam to reach the 9 micron target at the
other end to result in a recoverable signal is problematic.
If you're not pushing your distance too far it'll probably be fine, to
be honest.
Back in the day when I was working on large legacy campus fibre runs,
220 metres was the max distance we considered OK for SX drivers and OM1
fibre (for gig ethernet). Mode conditioning leads would push this out
to say, 900m trustworthy. If your distance is >900m I would suggest a
fibre upgrade is on the cards.
Again, the above all assumes mode-conditioning in use. If you're not
mode-conditioning your effective range is going to be very short - to
the point of unusability - and I'd be concerned about the affects of
'overdriving' fibre that is not set up for the use of low powered lasers
and was instead optimised for LEDs, which obviously put out a lot less
power.
Mark.
> Single mode just has a smaller core size for the smaller "beam" emitted
by
> laser vs. LED. it works although I've never done it outside of a lab (MM
> is cheaper). As for the distance it theory that should come down to the
> optics and your transmit power. Hopefully this is just a cable
connecting
> the router to a long line. I've never heard of a 10K MM fiber run since
SX
> optics can't shoot that far. You should be able to get through the 500m
or
> so that MM optics are rated for, but YMMV (errors, light levels, bounces,
> etc etc)Cisco gives specs for SFP LX over MM (they aren't that great at gig, and
really suck at
10G; if you have 50u OM3/OM4 you can do much better at 10G).See SFP/fiber/distance table at
Cisco SFP Modules for Gigabit Ethernet Applications Data Sheet - Cisco
They specify that line conditioning cables were used. I would say if
you're going to bother purchasing why not purchase SM?
We have run LX-over-MM (62.5) on short building runs as a band-aid until
SM is
available, and trying to do all new building MM with 50u OM3/OM4. We do
have some
dependence on 62.5u MM - used by our aging Simplex alarm system - which
does
point-to-point looped token ring <*cough*> on the alarm side.
What distances?
I'm trying to get them to confirm 50u will work point-to-point, but at
some non-alarm-points there would be a
necessary 50-to-62.5 exchange taking place and I'm not certain how to
accomplish that
(50->62.5 would likely have tolerable loss, but not 62.5->50).I don't think changing core sizes in the middle would work even with SM
optics.