Range using single-mode SFPs across multi-mode fiber

Thu Dec 15 18:46:53 UTC 2011

The max limit for 100 base FX (100 Mbps Ethernet) is around 6600 feet. Many campus ductbank systems built in the 1990s when 10 and 100 Mbps Ethernet were the commodity speeds (before GiGE) used 62.5/125 MM fiber to connect buildings. It is not unusual to see long MM runs on campus facilities where 100 Mbps backbones once were the fastest speeds available.

In those days, apart from longhaul telco use, singlemode fiber was usually only run for closed circuit TV (CCTV) use in the campus environment, and in places where 1990s SM was run for CCTV it can still be used for longhaul laser sfps, which to me shows that SM is future proof. SM even makes sense in short runs as attenuators can be placed on the send/receive strands to reduce the dB so the optical receiver is not saturated.

-----Original Message-----
From: Justin M. Streiner [mailto:streiner at cluebyfour.org]
Sent: Thursday, December 15, 2011 5:53 AM
To: Keegan Holley
Cc: nanog at nanog.org; oliver rothschild
Subject: Re: Range using single-mode SFPs across multi-mode fiber

On Wed, 14 Dec 2011, Keegan Holley wrote:

> 2011/12/14 oliver rothschild <orothschild at gmail.com>
> How did you end up with a MM run this long?  SX optics are only rated at
> 500 meters at best.  Even with mode conditioning jumpers more the 1km is a
> risk.  I'm glad it held up during testing though.  Just out of curiosity
> did you purchase dark from a provider?  Is it inside of a building?

Legacy 10baseFL/100baseFX/FDDI can run fairly long distances over OM1.
In the past I've run 100baseFX over OM1 runs with multiple cross-connects,
out to about 2 km.

jms

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