[c-nsp] Cheap 10G between 7600 and Procurve 5406zl

[Marian Ďurkovič]

On Thu, 18 Mar 2010 14:26:44 +1100, Lincoln Dale wrote
> > To be fair, Lincoln, Marian is talking about a different level of 
> > incompatibility going on here.  There are quirks in all hardware interfaces
> > (the free unix ethernet and SCSI drivers make interesting reading), but
> > getting good compatibility between 10G chipsets and arbitrary SFP+
> > transceivers is going to be a whole lot more difficult than writing a
> > driver to take into account that SFP+ model X does action Y in 
> > circumstance Z.  Analog to digital conversion is a black art.
> 
> for mainstream stuff - e.g. SR, LR etc. - there should be no issue.
> the devil is in the details of which getting into the gory technical 
> details probably isn't relevant here, but suffice to say that for 
> SR/LR i have not seen any interop issues but the more esoteric stuff 
> (CX1, LRM) have.

Yes, that's fully expected. SR and LR are trivial cases and thus most often
manufactured with limiting amplifier inside. They output zero if analog signal
is below a decision point and output one if above - i.e. the host sees digital
signal. Problems arise with linear SFP+ modules, which output analog signal.
 
> >> what is used behind the scenes (XAUI, XFI) has no bearing on you as
> >> an end customer AFAIK - beyond whether something is available or
> >> not.
> > 
> > It's not particularly the transceiver MII which is the problem here, it's
> > the form factor / end product.  XFP already delivers a good variety of 
> > optical interfaces, while X2 doesn't really come close in terms of range
> > or suppliers. 
> > This means that if you need an exotic X2, both purchase and 
> > support/replacement lead times are going to be bad.  This isn't a huge
> > problem if you're a large customer buying lots of kit, but if you're a
> > small customer, it's incredibly expensive to ask your local Cisco partner
> > to keep 10 different types of DWDM X2s in stock as spares.

> > In addition, by buying kit which takes X2 modules, you're committing a
> > huge amount of transceiver capex on a particular vendor (i.e. Cisco or
> > HP) which cannot then be moved to another vendor, because no-one else in
> > the industry uses them.  This is strong vendor lock-on.

I'll add a few points here:

1) (multirate) XFP is universal module - it can be used in LAN switches for both
LAN PHY and WAN PHY, in routers for both ethernet and POS interfaces, in
SONET/SDH equipment, in DWDM equipment, in various L1 converters/repeaters, etc.

2) XFPs don't contain XAUI->serial muxes/demuxes inside, thus need less power
and have lower latency.

3) XFPs have less electronics inside and are produced in larger quantities so
their price is much lower - it might well be around 1/2 of the X2 price.
 
That much from the customer's point of view.


  With kind regards,

     M.