I feel that TCP's self-clocking as illustrated in Van Jacobson's 1988
paper exists only if bottleneck link is a link of lower capacity (i.e.
bandwidth) than other links. However, if bottleneck link has higher
capacity than other links (i.e. the link is bottlenecked because a large
number of flows are using it simulateneously), there is no self-clocking
any more.
I don't think it is that simple
Self clocking always occurs -- you inject a packet in response to an ack and
the ack is telling you when the network has capacity for your new packet.
The issue raised in your note is whether the spacing of the acks reflects the
available bandwidth at the bottleneck. In most cases the answer is that
it reflects bandwidth only imperfectly. Ack compression, queueing disciplines,
etc., all conspire to muddy the spacing.
Craig
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