[c-nsp] SFP-10G-LRM in Nexus 5000

[Andrew Miehs]

LRM  works on SM. I have used them a lot on cat 4500s but we mainly but not only used them for OM1 cable.
Cisco link below:
http://www.cisco.com/c/en/us/products/collateral/interfaces-modules/transceiver-modules/data_sheet_c78-455693.html

Cisco SFP-10G-LRM Module
The Cisco 10GBASE-LRM Module supports link lengths of 220m on standard Fiber Distributed Data Interface (FDDI) grade multimode fiber (MMF). To make sure that specifications are met over FDDI-grade, OM1 and OM2 fibers, the transmitter should be coupled through a mode conditioning patch cord. No mode conditioning patch cord is required for applications over OM3 or OM4. For additional information on mode conditioning patch cord requirements please see: http://www.cisco.com/en/US/prod/collateral/modules/ps5455/product_bulletin_c25-530836.html.

The Cisco 10GBASE-LRM Module also supports link lengths of 300m on standard single-mode fiber (SMF, G.652).


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> On 15 Sep 2015, at 08:27, Nick Hilliard <nick at foobar.org> wrote:
> 
>> On 14/09/2015 23:15, Crist J. Clark wrote:
>> I am not exactly sure of the design decisions behind the choice to use LRM over
>> SMF to orginally connect the distro to the core when the campus was built. But
>> given that it was working, and we already had almost enough spare LRMs on hand
>> to complete the project, It Seemed Like a Good Idea at the Time.
> 
> Right. :-(
> 
>> We also have OM3 MMF between the buildings so replacing this all with SR is
>> the main plan right now, but whatever the problem is with the LRM modules
>> looks more like software/firmware than a problem with the fiber paths (the links
>> always do eventually come up with good light readings and no errors), and we
>> were just curious if anyone had seen this issue with 5ks and LRM before and
>> found a way to deal with it.
> 
> LRM transceivers are a bit of a curiosity tbh.  I've never seen anyone
> using them in production.  Because they're uncommon, this has the
> consequence that they will not be well debugged.  In many situation this is
> not a problem, but if you have dispersion problems, it can be, because
> dispersion compensation on 10G SFPs is handled on the switch / router
> motherboard.  I.e. this can easily be a software problem.
> 
> Also, if you're using LRM out of spec (SMF cabling instead of MMF), you
> should probably expect problems.
> 
> LR SFPs are cheap: ~$100 each for transceivers from reputable third
> parties.  You will save yourself time, money and heartache by sticking with
> LR over SMF for longer runs and not using MMF
> 
> Nick
> 
> 
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