From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Wed Aug 02 2006 - 18:54:49 ART
Rik,
I think that the order of things is reversed in your argument.
For short distances, led will suply enough light to reach the
destination, and MM fiber will be able to transport the
led's light.
For longer distances, you need lasers to compensate for the
attenuation you will have no matter what.
SM fiber will keep the light from bouncing too much, thus reducing the
dispersion and interference problems.
Bottom line: lasers are way more expensive.
Also, be careful to use some attenuators if you do use lasers in short
patches... you don't want to blind (saturate) your receivers...
I used to think that MM fiber should be cheaper than SM (because the
smaller core needs more precision), but was told that economies of scale
actually make it the other way.
Guyler, Rik @ 28/7/2006 12:37 -0400 dixit:
> There's a little more to it than that.
>
> MM fiber has several light pathways called modes. These light pathways
> within the fiber must all be used to get the maximum potential of the fiber.
> This is why SX transmitters are typically LED-based, which disperse the
> light across the various modes.
>
> SM fiber has a single light pathway or mode and so the light that travels
> through this type of fiber should be concentrated. Hence the reason why LX
> transmitters typically use lasers, which do not disperse light very much and
> can concentrate most of the light directly on the single mode. Because the
> light is concentrated and not dispersed, it will suffer much less
> attenuation and result in much greater distances.
>
> Using an LX transmitter with MM fiber can work for short distances (this
> will vary due to fiber and termination quality, number of cross connects,
> etc.) but because you are not able to light up all of the modes, this
> combination will suffer from attentuation significantly compared to matching
> them up correctly. Fiber mode conditioning cables were developed as a
> middle ground, allowing the use of an LX transmitter on much cheaper (or
> pre-existing) MM fiber. The conditioning cable is a MM patch cable with a
> splice of SM cable on the transmit side so it receives the full capability
> of the LX transmitter. The cable then distributes the LX output over the
> multiple modes of the MM fiber so you get the best of both worlds: a less
> expensive fiber cable plant but better distance numbers than you get with SX
> tranmistters.
>
> Rik
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Skinner, Stephen
> Sent: Friday, July 28, 2006 8:30 AM
> To: Cacca Mucca; Cisco certification
> Subject: RE: Running SFP LX/LH over MM Fibers
>
> What wavelength are you using
>
> Multimode simply means the cable is cable of running a wavelength of either
> 850 or 1300 or whatever.
>
> It is the circuit packs at either end which dictate what Wave your at.
>
>
> Are you running this on a circuit or back-to-back
>
> If its back to back , then aslong as your GBIC/SPF's match you will be ok .
>
> If it's running over a circuit then it depends on how the provider puts the
> circuit.
>
> If its an 850 length circuit and you put LH gbic at either end , your cisco
> switch won't work.
>
> HTH
>
> Stephen Skinner
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]
> Sent: 28 July 2006 13:09
> To: Cisco certification; Cisco certification
> Subject: Running SFP LX/LH over MM Fibers
>
> *** WARNING : This message originates from the Internet ***
>
> Just want to confirm, I have none to test with, that I'll be able to run
> LX/LH on multimode fibers.
>
> Thanks
>
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