On Wednesday 13 February 2008 20:08, Sean Hefty wrote:
> IMO, the fact that TCP implements reliability doesn't mean it's unnecessary in
> underlying layers.  For example, wireless typically adds reliability at the 
> link
> layer because the link itself is so unreliable.  If adding in reliability in 
> the
> underlying layers improves overall performance, then it makes sense to add it,
> independent of the upper level protocol.
> 
> Since RC is our 'link layer', overrunning the receiver doesn't just result in 
> IP
> resending the packet, but transitioning the QP into an error state, cleaning 
> up,
> re-establishing the connection, and then resending the packet.  This works, 
> just
> not well based on what Pradeep has seen.
> 
On the other hand, if the remote host is actually down, you will make "retry 
storms"
worse by retrying both at the link layer AND at the TCP layer (each TCP retry 
resulting
in multiple lower-layer retries).  This will have an effect on the fabric.

- Jack
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