[c-nsp] DWDM optics on 6500s

[Richard A Steenbergen]

On Mon, Oct 05, 2009 at 03:47:05PM -0500, Jeff Bacon wrote:
> Well that's wonderfully comforting. Though I really probably only need
> two ports anyway - ring-in and ring-out. Maybe not so bad. I'd consider
> a 720-VS-10G head if I had some confidence that those two ports on the
> sup were actually connected to the fabric. 

Can't tell you anything about the VS-10G, but if you're doing it on 6704
make sure you use 1 and 3, or 2 and 4, not 1->2 etc. Unfortunately I
have to deal with many hundreds of 10GE ports on 6704s (what can I say,
they're cheap :P), so we tend to try to pair them up as port-channels
(i.e. members 1/1 and 1/2, 2/1 and 2/2, etc) since this guarantees
traffic will never go in port 1 and out port 2 on any given fabric
channel.

> I don't really need to run line rate - this is more about latency and
> burst capacity than sustained throughput. I have loads that burst from 0
> to 500Mb/sec (then back) in nothing flat, and multiple of those may run
> through the wire at the same time. Or not. 

Yeah ok that won't challenge pretty much any hardware. :)

> Someone pointed out that the X2 and SFP+ xcvrs don't have much punch,
> and I'm going to be shooting 20-30km through passive MUXes. So that
> might matter.

X2 is nothing more than a physically smaller XENPAK case, the interface
and for the most part the components (if you take apart a modern XENPAK,
you'll see most of it is empty space) are exactly the same. Basically X2
only exists so lazy companies who don't want to redesign their boards
(Hi Cisco!) can keep using the same components from their old XENPAK
designs.

SFP+ is an entirely different beast, two generations removed from XENPAK 
(XENPAK->XFP->SFP), and with very low max power caps which prevent it 
from being used for most long reach/DWDM applications. Basically SFP+ 
only exists so you can stuff 48 10GE ports into a blade or 1U switch, 
but it's really only useful if you need to do a large number of short 
reach ports (i.e. datacenter aggregation). The only redeeming quality of 
SFP+ is you can finally get LR for them (I won't touch SR outside of 
same-rack applications, way too many problems) at not unreasonable 
prices.

XFP is still the best all-around optics platform for the full range of 
features, but unfortunately you'll see less and less focus here as 
everyone jumps on the SFP+ bandwagon as "the next new thing" even when 
it is completely unnecessary and infact only serves to limit function.

Slightly dated now (from feb 08) but mostly still accurate:

http://www.nanog.org/meetings/nanog42/presentations/pluggables.pdf

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
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