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

[David P. Reed]

The digital fountain idea (see Luby's theoretical work at SRC and Berkeley) 
is a great example of the benefit in multicast mode.

Recording data from a data source (whose rate is less than channel 
capacity) that generates data at a constant rate to a recipient's disk 
drive also benefits from out-of-order processing, if you want to avoid 
cumulative delay buildup.

Concurrent computation under optimistic concurrency control (see, for 
example, my 1978 PhD thesis) is another example where out-of-order delivery 
can pay off.

Gossip protocols (see recent work by Minsky, Trachtenberg and Zippel) also 
can benefit.


At 01:29 PM 9/17/2001 -0700, Amr A. Awadallah wrote:
>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
>
>