Re: comments on draft-kashyap-ipoib-connected-mode-02.txt

At 04:42 AM 12/11/2004, Margaret Wasserman wrote:
>At 09:19 AM 12/10/2004, Margaret Wasserman wrote:
>No.  It uses InfiniBand RC or UC to communicate IP datagrams (v4 / v6) 
>between connected endnodes.
>
>And what is InfiniBand RC, under the covers?

An InfiniBand reliable connection which is an IB transport type.  It isn't 
TCP or SCTP.


>Rest is based on a misconception as there is only IB below IP and no 
>tunneling of TCP over TCP occurs.
>
>Well, I know that there is another IP(v6) in there, as IB is very closely 
>based on IPv6.

I co-developed / led IB and aside from trying to align the addressing to 
IPv6, it isn't IPv6.  Never was my intention to have it be IPv6.

>   Is RC based on TCP? SCTP?

No.

>  Or did IB define a different reliable, connection-oriented IP protocol?

It is a connected oriented protocol that is not IP based.

>  If the latter, what type of retransmission and congestion control 
> algorithms are used by IB RC?

Retransmission is via a strongly ordered scheme thus there isn't the 
concept of SACK, etc.  This keeps it rather thin and easy to implement in 
hardware.  Congestion control was recently added and uses a variation of 
notification as well as selective back-off algorithms.

>   And, has there been any study regarding how they would interact with 
> the retransmission and congestion control algorithms of TCP or other 
> reliable upper-layer transports?

They are orthogonal as IB only guarantees a packet is delivered to an 
endnode.  It does not state anything about what occurs above.  So, in the 
case of IP over IB, if IP drops the datagram for whatever purpose, the 
associated transport or ULP will take appropriate recovery actions if 
desired.


>Even if this isn't TCP, per se, there may still be issues, but it will 
>take more careful research to determine what they are.

There are a variety of universities, etc. who are doing such research.  Try 
Ohio State to see what they have completed to date.

Mike

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