Re: [tcpm] draft-ietf-tcpm-tcp-uto-02

On Tue, Dec 13, 2005 at 01:24:32AM -0800, Fernando Gont wrote:
> At 10:25 a.m. 09/12/2005, Ted Faber wrote:
> >The mechanism described in 793 and 1122 is a perfectly reasonable
> >definition of a timeout system that an application could use to take
> >action if data's not delivered in a timely fashion.
> 
> The point is that if you;re really concerned about data being delivered, 
> you should be implementing an application layer timeout mechanism.
> If there's no TCP timeout, it does not mean that the data were delivered.

I understand the difference between a transport ack and acknowledgements
from higher layers.  Some applications (correctly!) use transport state
to synchronize application state.

Consider a file transfer appliaction that opens a TCP connection for
each file.  The connection is closed when the file is saved to disk.  A
transmitter knows the file has been delivered correctly if and only if
the receiver closes its connection correctly.  The receiver knows the
whole file has been transmitted when the sender closes its side of the
connection (a receiver never closes its connection before a sender
does).  Voila, application synchronization using TCP signalling. 

Such an application may well want to use TCP's existing UTO mechanism as
a timeout.

-- 
Ted Faber
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