Optical Fiber connection between GBIC module and SFP module

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Nov 10th, 2007
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I am in need of help.

I have a 3750 24TS-S, 2 port SFP, switch at the edge. And i have a 4507R switch at the Distribution layer. In 4507 switch I have WS-X4515 Sup IV supervisor engine with 2 GBIC Port and also have WS-4306-GB 6 port GBIC module. I am using WS-G5486 Single mode connector, LX/LH tranceiver to connect to this port.

This is the scenario.. i want to know is it posible to conect one end of the fiber cable to connect to a SFP Module ( 3750-24TS-S, 2 Port SFP) and other end ( WS-X4515 Sup IV supervisor engine with 2 GBIC Port or WS-4306-GB 6 port GBIC module) at the WS-G5486 Single mode LX/LH connector ?????

Plz let me now asap.. i need to give a solution imdtly.

Thanks & regards


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sarfaraz1981 Sun, 11/11/2007 - 00:45
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in this scenario u need a ST-LC fiber cable to connect one side gbic to sfp.

mahmoodmkl Sun, 11/11/2007 - 00:46
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Yes u can connect using the above GBIC and SFP.



cfarnsworth Thu, 11/22/2007 - 22:10
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Similar I would like to connect 3550-12G (GBICs only) to 3560-24SMI (SFPs only) via multi-mode fibre. Do I just need the fibre lead to have a SC connector fitted on one end and a LC connector on the other?

scottmac Sun, 11/11/2007 - 09:08
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You need a jumper with the correct physical connections (SC/LC, I believe, as mentioned above) BUT, more importand, is that both ends must be the same from a protocol perspective. Both must be SX, LX, ZX .... whatever.

If you connect the two devices and one is meant for long-haul, you can burn out the receiver on the other side.

If both sides are the same, bith are meant for long-haul, but the devices are not really as far apart, then you need some of optical attenuator. IF you are using something meant to go kilometers and you're only going a a few hundred feet, you (almost certainly) need attenuation ... or you'll burn out the receivers (or de-sensitize them).

Good Luck


rajatsetia Mon, 11/12/2007 - 02:29
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Hi Scott,

I read your post and wanted to ask you something out of the curiosity.

You said that if you use long-haul GBICs/SFP but the devices are not far off then receivers will be damaged.

I was thinking if these long-haul receiver are capable of generating the strong signal and are not they capable of receiving the same signal strength ( if we use these for short distance) ? I hope i understood your point and asked the genuine query :)

If you have experienced the receiver burnout in running environment, I can't deny you as I have no proof to say it otherwise and won't like to experience it.... who would like to burn out the receivers :)



scottmac Mon, 11/12/2007 - 07:36
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Discussion is never a problem ....;-}

The issue is that the signal is "too loud" and is distorted (or, more correctly, is so loud it overloads the receiver).

The operational envelope for nearly every receiver of any kind includes a bottom number (too weak to hear) and a top number (too loud to understand).

As an example, think about an system where you have a hearing aid that would let you hear someone speaking in a normal voice from 100 feet away ... then having someone scream the same words into the hearing aid from 6 inches away ... the sound would be distorted and you would have difficulty understanding them ... after a while, you'd begein to go deaf and eventually, it would sound normal (until you became completely deaf).

So, what you need to do is look at the transmitter power, and the envelope/range of acceptable power the receiver can hear.

Normally that difference is the optical budget ... given the loss numbers of the media between the two, you can determine if you have enough power to make the trip.

In a Lab environment, you still have to hit the receiver's budget number, but from the other end (the "too high" side).

If you know the transmitter puts out X, and the receiver can accept from Y to (X-50), then you need to add enough attenuation to get X down to (X-50)or lower (but still more than Y).

When you have a transmitter powerful enough to drive tens of kilometers, putting one two meters away from the receiver will pretty much guarantee a burnout (unless you install optical attenuation).

Good Luck


rajatsetia Mon, 11/12/2007 - 09:01
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Thanks for your quick response.

your point is totally valid about the upper and lower limit of trasmit and receive power, basically i was cusrious about if there is difference is upper limit of transmit and receive power same optics.

if the upper limit for trasmit and receive is same then optic should not burn out even if i connect the optic with a patch cord.

like if trasmit upper limit of a long haul sfp is -3 dbm and receive upper limit is also -3 dbm then this sfp should not brun out even if connecting the both ends with a patch cord.

i checked one of the sfp datasheet in cisco and this is what i have found- 'it could be either case, upper limit could be same or not' so as you suggested its better to check out the specifications before using the long hauls for small distance.


thanks for your inputs, hope i got it right this time :)




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