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

[Amr A. Awadallah]

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
> 
>