On Sun, 2005-10-09 at 10:19, Sean Hefty wrote:
> >I think iWARP can be on top of TCP or SCTP. But why wouldn't it care ?
>
> I'm referring to the case that iWarp is running over TCP. I know that it can
> run over SCTP, but I'm not familiar with the details of that protocol. With
> TCP, this is an end-to-end connection, so layering iWarp over it, only the
> endpoints need to deal with it. I believe the same is true for SCTP.
Yes, SCTP is similar in those regards.
buffers and credits. So SCTP will allows multiple in-flight messages for each
RDMA stream in the association.
Yep. This is where iWARP differs from IB RD in that IB restricts this to a single in-flight message per EEC at a time while iWARP allows multiple in-flight over either transport type supported. The logic behind why IB RD was constructed the way it was is somewhat complex but one of the core requirements was to enable a QP to communicate across multiple EEC while preserving an ordering domain within an EEC. Given all of this needed to be implemented in hardware, i.e. without host software intervention, for both main data path and error management, the restriction to a single message was required. I and several others had created a proprietary RDMA RC followed by a RD implementation 10+ years ago so we had a reasonable understanding of the error / complexity trade-offs. Given the distances were within a usec or each other and one could support multiple EEC per endnode pair, the performance / scaling impacts were not seen as overly restrictive and met the software application usage models quite nicely. Anyway, there are differences between iWARP / SCTP and IB RD so people cannot equate them beyond some base conceptual level aspects.
Mike
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