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silentsigma
Beginner

cisco GLC-SX-MMD transceiver fiber cable max length

I'm using a GLC-SX-MMD transceiver and some fiber cable to connect my remote switch to my core switch. Looking at cisco documentation, it said that the operating distance is 275 ft because the fiber cable is MMF 62.5 um. But, when I use the OTDR fiber device, it is reading that the length of the cable is around 1400 ft. My question is, does it matter how long the fiber cable is as long as the transceiver transmit and receive power is within the spec range?

2 ACCEPTED SOLUTIONS

Accepted Solutions
chrihussey
Collaborator

The documentation says it can go 275 meters which is about 902 feet.

Yes the distance of the fiber plays a part. As the light travels down the fiber there is dispersion and degradation of the signal. In many instances you can exceed the cable distance as your mileage will vary. In your case you are really pushing it. However, in the end it is best to adhere to specifications. It could work today and then start generating errors at some point, or just be flaky, especially when it is moving a lot of traffic.

BTW - If you use LH/LX optics with mode conditioning path cords, you could go up to 1804 feet (550m) on the 62.5 fiber.

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fiberstorejames
Beginner

You should adhere to the specifications of the cable. Becasue the linking length of Multimode fibers is limited by modal dispersion and chromatic dispersion, multi-mode fiber has higher pulse spreading rates than single mode fiber, limiting multimode fiber’s information transmission capacity. Therefore, if the multimode fiber is utlized in longer distance than 275 ft, it may cause an error to your network.

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5 REPLIES 5
chrihussey
Collaborator

The documentation says it can go 275 meters which is about 902 feet.

Yes the distance of the fiber plays a part. As the light travels down the fiber there is dispersion and degradation of the signal. In many instances you can exceed the cable distance as your mileage will vary. In your case you are really pushing it. However, in the end it is best to adhere to specifications. It could work today and then start generating errors at some point, or just be flaky, especially when it is moving a lot of traffic.

BTW - If you use LH/LX optics with mode conditioning path cords, you could go up to 1804 feet (550m) on the 62.5 fiber.

View solution in original post

BTW - If you use LH/LX optics with mode conditioning path cords, you could go up to 1804 feet (550m) on the 62.5 fiber.

Yeah I'm thinking of doing that. I have one run that is 2000 ft which is over the recommended distance limits and putting a switch in the middle will be costly and not to mention we don't control over that place. It seem like if one of my run that is 1400 ft is doing fine on a 900 feets limit; I should try the LH optics with mode conditioning paths cords to see how it goes.

Also, if I used the mode conditioning path cords, do I have one on  both ends or just one end is good enough? 

Mode conditioning patch cords are needed on both ends and have to be used in the proper direction.

They have a transmit and receive. On the receive side (to the switch port) it is a straight through multi-mode fiber. On the transmit side (from the switch port) it is a single mode fiber spliced to a multi-mode fiber so the light is launched at the proper angle. So when ordering these cables you need to keep this in mind when specifying the connectors on either end and make sure you use it properly.

kayukovvalera
Beginner

Hi,

Use please doc:

http://www.cisco.com/c/en/us/products/collateral/interfaces-modules/gigabit-ethernet-gbic-sfp-modules/product_data_sheet0900aecd8033f885.html

Table 2.       Main Optical Parameters

Transmit Power Range (dBm): -3 to -9.5

Receive Power Range (dBm): 0 to -17

Now we will calculate:

min optical buget: |-9.5| - 0 = 9.5 db 

max optical buget: |-17|-|-3|=14 db

You can measure it with power meter and with attenuator. Then calculation budget for particular SFP. Then you have to compare it with loss between mark A(start of fiber) and mark B(end of fiber) on OTDR trace. If loss on fiber greater than actual\spec-based budget than it might will not work.

fiberstorejames
Beginner

You should adhere to the specifications of the cable. Becasue the linking length of Multimode fibers is limited by modal dispersion and chromatic dispersion, multi-mode fiber has higher pulse spreading rates than single mode fiber, limiting multimode fiber’s information transmission capacity. Therefore, if the multimode fiber is utlized in longer distance than 275 ft, it may cause an error to your network.

View solution in original post

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