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Chapter 6
Meters, queues and IPQoS
E-NIT-CTC-20041213-0013 v0.5
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Ackfiltering
Example
The figure below illustrates how ack filtering is done.
An upload data stream is exists (data packets). Meanwhile a download TCP
connection is generated as well. TCP-based downloads can only continue if the
remote site receives ACK packets for each data packet it sends. As we can see in
the figure above there are two ACK packets in the queue. To avoid delay we will only
send the second ACK packet and drop the first ACK packet. If the remote site
receives ACK2 it will know that everything that was sent before was OK. If ACK
filtering is turned off both the ACK will be send, causing delay.
ackfiltering value Description
enabled If the ackfiltering option is enabled duplicate ACK
packets in a queue will only be sent once. Meaning
that the last duplicate ACK packet will be sent and the
other ACK packets will be dropped
disabled If the ackfiltering option is disabled all ACK packets
will be sent in their original sequence.
ACK filtering happens on a per TCP-connection base.
Data ACK1Data DataACK2