Broadband Optimizer for Revolution?

[Alex Tweedly]

Dar Scott wrote:

>
> I couldn't find any reference to "transmit window" or "slow start" in 
> rfc 793.  I don't see how it's part of TCP, proper.  

"transmit window" came into common usage sometime around the early 90s - 
to refer to the sender's view of the congestion window. An application 
trying to figure out if it is near to congestion (and perhaps vary the 
info it is sending accordingly) should probably use this rather than the 
size of the congestion window (though of course, since it's TCP not 
everyone agree on that).


slow start (and congestion avoidance - independent ideas but a merged 
implementation)  was first described and implemented by Van in 1988, and 
then in  rfc 1122 (Host requirements) congestion avoidance became a 
required feature for TCP implementations. It became a formal part of the 
rfc system in rfc2001 - but that was long after it had become common.

slow start undoubtedly is part of TCP proper; the use of the term 
"transmit window" is not defined by any rfc (afaik - didn't search to 
check), but is ubiquitous in the IETF community. I think the term 
transmit window is worthwhile since it expresses the fact that the 
congestion window being used is that seen by the sender, whereas the 
congestion window can be manipulated by both sender and receiver.

> The "send window" is really just the senders view of the standard TCP 
> window and should not refer to self-limitations of the sender.

> Even so, thanks for this info.
>
> I think you're saying that the "congestion window" used by some 
> implementations is limited by both the TCP window (called "receive 
> window" by some) and some configuration called the "transmit window".
>
Not quite - see the terminology in rfc2001 (slightly different from what 
793 had used).
The advertised window is what the receiver advertised.
The congestion window is the sender's modification of that - varied both 
by sender's configuration and more importantly by congestion that has 
occurred.

> This imposes a minimum on the transmit buffer size, and it seems you 
> are saying that the practice is also to make this the maximum on the 
> transmit buffer.  Did I get that right?
>
No, I don't think it imposes a minimum on the transmit size; why would it ?

-- 
Alex Tweedly       http://www.tweedly.net



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