[c-nsp] SFP+ modules in Catalyst switches (was: Nexus 7000)
Richard A Steenbergen
ras at e-gerbil.net
Tue Jan 29 18:39:48 EST 2008
On Tue, Jan 29, 2008 at 09:22:53AM +0100, Marian ??urkovi?? wrote:
> On Mon, Jan 28, 2008 at 11:07:13PM -0500, David Prall wrote:
> > It uses SFP+'s, they supposedly will be available in both 1GE and 10GE.
>
> While the move to SFP+ for the Nexus7000 is clearly the only solution
> (datacenter needs high density & low cost 10GE links and Nexus has
> the potential for 500 Gbps per slot), the SFP+ datasheet says it will
> also be adopted in Cat6000/4000/3000 series.
>
> Could someone please explain the motivation for this?
>
> >From the customer's perspective, it's a nightmare to see fourth different
> 10GE form factor coming into e.g. Cat6500, especially when XFPs were
> already used on 10GE SPAs and ES20 cards. Consolidation on XFP form
> factor would be IMHO much better for several reasons:
>
> - it's also XFI-based
> - all types are available *now* (including CX4, ZR and DWDM which are not
> planned for SFP+)
> - supports both LAN and WAN PHY
> - offers sufficient port density (24) for 80 Gbps per slot backplane
> - has the widest adoption rate as it's used in SONET/SDH, DWDM and ethernet
> equipment
> - is subject to continuos inovation (tunable XFPs, ultra long reach XFPs
> etc.)
Don't forget, SFP+ is limited to such low power (1.5W in the highest power
class) that it is all but impossible to ever power long reach optics (40km
or 80km+) with them.
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.
--
Richard A Steenbergen <ras at e-gerbil.net> http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
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