On Tue, 18 Dec 2007, Paula Minor wrote:
Tom P said:
Normally, DSL should not do that. This implies that some bandwidth
is being consumed by NACs. The speed measuring sites do not seem to
register NACs.
Tom, what is "NAC"?
I think he means what I call "NAK" or "Negative AcKnowledgement".
In TCP, data which doesn't arrive at the destination (or arrives in
corrupted form) must be transmitted. Every so often, each side will
transmit an acknowledgement of what data has been successfully received
by that side of the connection. If no acknowlegement of a piece of
data is received within a certain amount of time, the sender of that data
assumes it has been lost or corrupted, and must be retransmitted. It's
this time spent waiting for an acknowledgement (ACK) and the repeated
transmission of the lost block of data that lowers the effective
bandwidth of your connection. Note: I _think_ that TCP only uses
"positive acknowledgement", and simply relies on the same timeout
mechanism for both lost and corrupted data... i.e. it doesn't actually
send a NAK when data is received but found to be currupted.
(any of you other network geeks feel like checking the RFC to make
sure I'm correct?)
--
Vicky Staubly http://www.steeds.com/vicky/ [EMAIL PROTECTED]
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