[e2e] SEuCN

Ivica Rimac rimac at bell-labs.com
Mon Nov 7 12:54:02 PST 2005

Hi Jon,

> so reading re-feedback etc, and loss notification, wouldn't it be easier
> given most flows have feedback packets, to have an efficient common case
> encoding 
> 1// the hop count in the net is rarely more than 32
> so lets have a 32bit field which is called SEuCN
> and is 
> Selective Explicit unCongested Notification.
> in outbound backets, each hop sets this bit
> (and its returned in acks) to say "all is well and good here".

I am curious how each hop would determine the bit it should set? 
Furthermore, since the bit is set in case there is no problem, how 
should an end node know that the x Zeros of the 32/64 bits are not an 
indication of problems but rather that the number of hops the packet 
passed is qual to 32/64-x? Hmm, might use the TTL field to determine the 
hop count and determining the corresponding bit at each hop ...
But naivly asking, what do we gain for the transport layer mechanisms if 
we know how many hops are congested?
It seems to me like the congestion level is much more interesting in 
order to apply different algorithms at different congestion levels on 
the transport layer (e.g., more aggresive increase algorithms, etc.), 
which however would require some mechanisms in the routers.

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