[c-nsp] SFP+ modules in Catalyst switches (was: Nexus 7000)

[Marian Ďurkovič]

On Tue, Jan 29, 2008 at 06:39:48PM -0500, Richard A Steenbergen wrote:
> The motivating factor behind SFP+ is the ability to do high port density 
> and crazy oversubscription, since SFP+ is so much lower power than XFP. 
> Note that if you compare the same types of optics (i.e. SR to SR, LR to 
> LR), the power difference between SFP+ and XFP is minimal (yes you're 
> offloading a CDR component, but you're just moving it off to the host 
> board so in the end you stay pretty neutral). The difference is that SFP+ 
> has no higher power classes (2.5W or 3.5W as in the case of XFP long 
> reach), therefore it will never be possible to put a long reach optic in 
> one, therefore you can "safely" design a 36 or 48 port card for them.
> 
> This is fine if all you're doing is datacenter or small campus stuff, but 
> completely destroys the capability to do long reach/DWDM optics over dark 
> fiber. Personally I suspect that SFP+ is not going to be particularly 
> popular with the SP crowd, and any vendor who values their business should 
> make a high-density (16-port or so) XFP blade alternative as well.

Unfortunately it seems Cisco now tries to completely avoid XFPs on 
ethernet linecards for Catalyst switches.

In the past they were too conservative and selected X2s because of LX4 and CX4
support. Ironically, just a few months after X2 linecards appeared, the XFP
camp released CX4 XFPs and eliminated the need for LX4 by LRM. So at present,
XFP platforms enjoy full range of optical interfaces at much lower cost,
while X2 product line is expensive and still not complete - no ZR/DWDM,
tunables may not appear at all.

Despite of this, new linecards are still released with X2 slots - e.g.
the most recent WS-X6716-10GE.

Now what matters is which formfactor will get onto the next-generation
ethernet linecards for 80 Gbps/slot Supervisor2080 - if SFP+, there will
be again the same problem with lack of long reach / DWDM optics...


	M.