[BXXPwg] Multiple sequence frames

Marshall Rose mrose@dbc.mtview.ca.us
Wed, 19 Jul 2000 22:31:04 -0700


> Hmmm...  it seems legitimate to me to reduce a window, provided that the
> receiver can still handle any outstanding data legitimately sent according
> to the then-current window values.  I.e. if the window is reduced, buffer
> space may be reclaimed only as data is received.
>
> This may require some slightly fancy implementation footwork, but only for
> receiving systems that allow the window size to be reduced.

well, either way we have to add clarifying text, but let me try to convince
you that "reducing a window" is equivalent to "breaking a promise".

if a receiver says "i am willing to accept upto XXX octets", then a sender
may immediately transmit up to that many octets, or less than XXX octets, or
none. regardless of the choice, it is all predicated on the promise that was
made by the receiver. if the sender transmits all XXX octets, and
simultaneously, the receiver shrinks the window, then you have breakage.
this doesn't seem fair: the receiver shouldn't have advertised a window that
large unless it had already reserved the space for it.

remember, the receiver doesn't have to keep opening up the window as it
buffers data. if it becomes constrained, it decides whether to issue further
updates. if it doesn't, the sender must stop when it exhausts the original
window.

/mtr