[c-nsp] Overclocking HSSI interfaces

[Robert E.Seastrom]

Bernhard Schmidt <berni at birkenwald.de> writes:

> Hi,
>
> we have a supplier who wants to sell us a satellite modem doing about
> 75Mbps throughput with one single HSSI connector. They claim they
> already used this successfully with a standard PA-HSSI in a standard
> 7200 box (running full 75Mbps on HSSI).
>
> Has anyone any experience with that? I seriously doubt it is possible at
> all (not to talk about stability), since all documents I found regarding
> HSSI talk about 52Mbps speed max and I don't think 50% overclocking is
> possible at these rates.

Although the HSSI standard was specced for 51.84 Mbps max, it was
intended to be extensible to faster speeds (see section 1.0 at
http://www.cisco.com/warp/public/459/8.html - they had an eye on
STS-3), so electrically it's very likely that HSSI should be capable
of some degree of overclocking.  The only question is whether the
Muselix chip will put up with it (I can hear a collective groan coming
up from our riends at Cisco right now).

I'd think your odds of success would go up with the following:

Rev. B PA-H or PA-2H cards
Short (3m or less) HSSI cable runs (maximum spec length is 15m)
High-quality HSSI cables (ie, don't try to use a scsi narrow cable
like someone did a scant decade ago; he left me to debug the mess)
VXR router (not plain 7200)

HSSI cards are dirt cheap - the PA-H Rev B that's at the top on eBay
right now is somewhat overpriced (in my experience) at $55.  Nothing
succeeds like success; I'd cobble something together in the lab and
fire up your Ixia, Smartbits, stream.c, pressure washer, or whatever
else is involved in your favorite torture test.

                                        ---Rob