[c-nsp] Long range 10G ethernet?

[Justin M. Streiner]

On Wed, 16 May 2012, Peter Rathlev wrote:

> (On 6500/Sup720 and with LAN cards)
>
> We're currently using a gigabit link with a total loss of 24.1dB (at
> 1510 nm) from end to end. We're using some third party "120 Km"
> transceivers, and this is working well.

I ended up doing something similar about two years ago on a pair of ~110Km 
dark fiber links at 1G, but using external line drivers from Transition 
Networks.  While I would have preferred to use native Cisco optics to 
drive the link, there wasn't anything available that I could plug into 
a 6509 that would drive a link that far.  To Transition's credit, the 
links have been absolutely solid in the nearly two years they've been in 
production.

> Now we're thinking about making it a 10G link instead. Finding 10G
> transceivers capable of supporting at least ~24-25dB seems tricky
> though. Googling a bit reveals something like the Optospan
> SPP-81D-K080T31, rated for 25dB at 1310nm. Of course we're primarily
> using X2 transceivers, and that one is an SFP+.

What is the distance of the fiber span?  It's somewhat surprising that the 
published link budget on the equivalent 1550nm module is lower - by 2 dB, 
which is substantial - than the 1330nm module.

> 1) Any general ideas about how to best run 10G on 25+dB stretch without
> external amplification? We'd like to avoid the extra complexity that
> would introduce.

25+ dB is really pushing the envelope of what you can get out of something 
you can plug into a switch, without amplification/regen.

> 2) We might cut ~1dB by splicing in a few places instead of patching,
> but we probably can't get below 23dB loss. Would using 25dB capable
> transceivers on a 23dB stretch be too bold for comfort?

Does your link budget include the insertion loss from the jumpers that 
will connect to your equipment at each end?  It might seem like splitting 
hairs, but on a link with that much loss, 2 dB can make a lot of 
difference, especially if the insertion loss cuts your headroom down to 1 
dB, or even less.

> 3) Does the OneX converter support any SFP+? Or is it somehow locked to
> only support certain modules? Cisco[1] mentions only CU, SR and LR as
> supported. Any (electrical) reasons OneX couldn't support any kind of
> SFP+? Should we count on being able to use e.g. the aforementioned
> SPP-81D-K080T31 in a OneX in e.g. a 6708 or Sup2T port?

Not sure about this one.  Haven't messed around too much with the OneX.

jms