from the academic side of the house

Jim Shankland nanog at shankland.org
Tue Apr 24 16:24:13 UTC 2007


bmanning at karoshi.com writes:

> The next day, the team used a modified version of TCP to achieve an
> even greater record. Using the same 30,000 km path, the network was
> able to achieve a throughput of 9.08 Gbps which is equal to 272,400
> Tb-m/s for both the IPv6 multi and single stream categories. In doing
> so, the team surpassed the current IPv4 records, proving that IPv6
> networks are able to provide the same, if not better, performance as
> IPv4.

Good job.  Two questions, though:

(1) Do the throughput figures count only the data payload (i.e.,
anything above the TCP layer), or all the bits from the protocol
stack?  If the latter, it seems a little unreasonable to credit
IPv6 with its own extra overhead -- though I'll concede that with
jumbo datagrams, that's not all that much.

(2) Getting this kind of throughput seems to depend on a fast
physical layer, plus some link-layer help (jumbo packets), plus
careful TCP tuning to deal with the large bandwidth-delay product.
The IP layer sits between the second and third of those three items.
Is there something about IPv6 vs. IPv4 that specifically improves
perfomance on this kind of test?  If so, what is it?

Jim Shankland



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