[openib-general] [ANNOUNCE] Contribute RDS (ReliableDatagramSockets) to OpenIB

[Bob Woodruff]

Woody wrote, 
>Perhaps if tunneling udp packets over RC connections rather than
>UD connections provides better performance, as was seen in the RDS
>experiment, then why not just convert
>IPoIB to use a connected model (rather than datagrams)
>and then all existing IP upper level
>protocols would could benefit, TCP, UDP, SCTP, ....

Saying this another way.
Make the hardware run the existing protocols better, don't
design a new protocol to work around the problems with a
specific hardware transport.

woody




-----Original Message-----
From: Caitlin Bestler [mailto:caitlinb at broadcom.com] 
Sent: Friday, November 04, 2005 2:31 PM
To: Woodruff, Robert J; Rick Frank; Ranjit Pandit; Grant Grundler
Cc: openib-general at openib.org
Subject: RE: [openib-general] [ANNOUNCE] Contribute RDS (
ReliableDatagramSockets) to OpenIB

 

> -----Original Message-----
> From: openib-general-bounces at openib.org 
> [mailto:openib-general-bounces at openib.org] On Behalf Of Bob Woodruff
> Sent: Friday, November 04, 2005 2:15 PM
> To: 'Rick Frank'; Ranjit Pandit; Grant Grundler
> Cc: openib-general at openib.org
> Subject: RE: [openib-general] [ANNOUNCE] Contribute RDS ( 
> ReliableDatagramSockets) to OpenIB
> 
> Rick wrote, 
> >I've atttached a draft proposal for RDS from Oracle which discusses 
> >some of
> 
> >the motivation for RDS.
> 
> Couple of questions/comments on the spec.
> 
> 
> AF_INET_OFFLOAD should be renamed to something like AF_INET_RDS.
> 
> Would something like SCTP provide the same type of 
> capabilities (relaible datagrams) that you are suggesting to 
> add with RDP ?
> 

Each stream within an SCTP association provides a reliable,
ordered service.

There would be two primary constraints in using SCTP for
this usage profile:

1) The Stream ID is 16 bits, and the natural mapping would
   be to have each stream represent a source/destination
   pairing. That would imply fewer than 256 endpoints per
   host. If the source were encoded by hand then the limitation
   would be 64K, but that's an awkard mix of application and
   transport layer encoding.
2) The network has to be composed of SCTP friendly equipment.
   When IP network equipment operated exclusively at L2/L3,
   and L4 was left to the endpoints, SCTP would have had no
   problem being deployed. But because of security and IPV4
   address shortages there are a lot of middleboxes that are
   L4 aware, and generally that L4 awareness is limited to
   TCP and UDP.

SCTP support would also have to be part of the offload device.
RDS enables reliable datagrams using existing offloaded RC
services (IB RC, iWARP, TOE). No NIC enhancements are required.




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