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GBIC SX Maximum Transmission Distances


In all Information I can find about transmission Distances for Gigabit SX there is a parameter "MODAL BANDWITH" which makes the range to go from 220 to 275 meters using a 62'5 micron fiber depending if its value is from 160 to 200 MHz km.

¿is this a parameter of the type of fiber?, and if yes ¿how can I check this parameter for calculating the maximum transmission distance?



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Re: GBIC SX Maximum Transmission Distances

Any updates on this? Pls help.


Re: GBIC SX Maximum Transmission Distances

My cable guy says its the result of tests done after the cable is installed. Depends on the quality of splices and teminations. Dont know how you can plan if thats true.

Re: GBIC SX Maximum Transmission Distances


Then if depends of the installed type or quality of fiber, anybody knows any show command for knowing in the cisco device if it is using 850 nm or 1300 nm?



Re: GBIC SX Maximum Transmission Distances

Modal bandwidth is a performance characteristic associated with multimode fiber, measured in MHz*km. Attenuation at a particular wavelength of light is another, measured in dB/km.

If you can identify the manufacturer and part number of cable installed, then you can verify the modal bandwidth and attenuation parameters for your particular cable by visiting their website or calling their tech support. If not, then assume the worst-case scenario for the size fiber you have (62.5/125um, or 50/125um) and go from there.

Manufacturers typically specify modal bandwidth as something-slash-something else: for example, 160/500 MHz*km. The first part (160 in this case) is bandwidth at the 850nm wavelength, and the second part (500 in this case) is bandwidth at the 1300nm wavelength.

How this relates to Gigabit Ethernet: Cisco's SX GBICs operate at 850nm, while their LX/LH GBICs use 1300nm.

Once you know the kind of fiber you have, you have a general idea what distances the IEEE 802.3z Gigabit Ethernet standard will support over your fiber. The actual distance you can go reliably depends on the strength of the optical transmission, the quality of the fiber itself, and how well the fiber was installed. The dB losses due to inherent attenuation of the fiber, fusion splices, connectors, and sharp bends in the fiber all conspire to limit the distance a usable signal can travel.

Equipment manufacturers typically specify the minimum and maximum transmit and receive capabilities of their optical transceivers. From the minimums you can calculate a link loss budget, the worst-case scenario with regard to transmitted signal strength. As long as the accumulated attenuation in the fiber span is less than the link loss budget, the span will work fine. So, it is possible to push the signal past 220 to 275m on 62.5/125um MMF, if you have a good fiber install; that span just won't be compliant with the standard.

Optical power meters can be used to measure end-to-end attenuation at a given wavelength in a fiber span. Optical time domain reflectometers can also do this, and much more, but are more expensive.

FYI, while most 62.5/125um multimode fiber is limited to 220 to 275m for Gigabit Ethernet, and 50/125um MMF is limited to 500 to 550m by the specification, there are manufacturers out there (Corning is one) that are producing 50/125um MMF with much higher modal bandwidths. This premium fiber allows Gigabit Ethernet distances out to 2000m on new installs, with the appropriate equipment.

Hope this helps.

Re: GBIC SX Maximum Transmission Distances

Really this helps and clarify it.


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