[bdNOG] Service level effect in SM-MM fiber combination

Wed Feb 24 21:25:09 BDT 2016

On 24/02/2016 14:18, Md. Abdul Awal wrote:
> We have a probable link to provision with a SM-MM-SM fiber combination 
> shown below:
>
>
> 
> Wondering if there is any issue in terms of QoS, data flow or any 
> other service related problem in the long run. I'd appreciate your 
> comments on that.

I would strongly recommend you don't do this: the amount of light which 
can get from the MM into the much narrower SM is very low, and the 
majority will be reflected back.

What interfaces are you using at each end? A 1000baseLX SFP is capable 
of running over either MM or SM, so if you simply use SM patch cords at 
both ends then it's SM end-to-end, and all the problems go away.

If you are using 100baseFX media convertors then it might work, but 
media convertors are unmanaged and notoriously unreliable. Putting an 
SFP in a managed switch will be a much more robust solution.

Something like the Netgear GS110TP costs about $150 and gives you two 
SFP ports, 8 gigabit copper ports (with PoE!), and is fully manageable 
(SNMP, HTTP, and telnet on port 60000)

Regards,

Brian.

P.S. There are special "mode conditioning patch cords" you can get, but 
these are used for the opposite situation - i.e. where the long link is 
multi-mode and the tails are single-mode. (The idea is to get slightly 
longer reach from existing MM plant)
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