[e2e] What's the benefit of out-of-order processing?

[Sam Liang]

Amr,

  You suggested an interesting way to transmit a large file.  However,
just as you alluded to, how are you going to do congestion control if you
don't send back any intermediate feedback with ACKs?  Congestion control
is a complicated problem. 

  You want to reduce the number of ACKs the ftp server processes, I think
we should try to figure out a way to reduce the ACK frequency, which still
provide certain feedback to the sender for congestion control purpose.

Sam


> 
> Large file downloads is a very good example application. For example, a 1GB 
> can be sent in any order with no retransmission, then at end of the cycle a 
> single NACK is sent for all missing packets and then iteratively go through 
> the next batch and so on until all packets belonging to the file are 
> delivered. Some loss signaling will still be needed for TCP congestion control 
> to work. This might not lead to much improvement of goodput (since all packets 
> still need to be delivered), but it simplifies the task of an ftp server with 
> many receivers, since it does not need to handle as many ACK packets.
> 
> Take a look at the work from digital fountain:
> 
> http://www.digitalfountain.com/technology/library
> 
> -- Amr
> 
> Sam Liang wrote:
> 
> >   RFC2960 for SCTP lists the lack of out-of-order processing as the first
> > major drawback of TCP:
> > 
> >    "TCP provides both reliable data transfer and strict order-of-
> >     transmission delivery of data.  Some applications need reliable
> >     transfer without sequence maintenance, while others would be
> >     satisfied with partial ordering of the data.  In both of these
> >     cases the head-of-line blocking offered by TCP causes unnecessary
> >     delay."
> > 
> >   Is there any study done on evaluating the effect of this TCP
> > "deficiency"?  What applications really need to and are capable to do
> > out-of-order processing? Can video over IP or voice over IP applications
> > process frames out-of-order? With SCTP's order-of-arrival delivery, how
> > much performance boost can be achieved over TCP, in terms of increased
> > throughput and reduced delay?
> > 
> >   Thanks,
> > 
> > Sam
> > 
> > 
> 
> 
>