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Z-Ice 05-24-2004 02:08 PM

Delayed ACK
I was wondering if anyone knows the timeout for delayed ACK in the kernel 2.4.26? I am using a wireless network and I used ethereal to capture my packets. I noticed many steps in the graph and I feel it is the timeout of the delayed ACK. I was wondering if anyone knows what it is set to or if there is a set number of packets? The delayed ack works fine throughout a transfer I get 2 packets in and one ack back out. After an amount of time(~4.7sec) I get steps. After a while it catches back up and goes on normally. It repeats many times throughout the transfer.


Mara 05-24-2004 03:00 PM

Are you sure it's bacause of ACKs? Probably it's because of losses? They're quite high when using radio.

Z-Ice 05-24-2004 03:12 PM

No losses
I looked through the tcpdump and it is not radio losses. Or lost acks. I know delayed ack is running. The 'steps' happen in such a non-random order. There was no interference channels running. I know delayed ack has a timeout: Take a look here I was wondering when 2.4.26 default is? I need to solve/understand the problem.

Mara 05-24-2004 03:44 PM

Probably that's it:

#define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
(in include/net/tcp.h)
HZ = 1 sec.

Mara 05-24-2004 03:46 PM

Moved to Linux - Networking as it's a technical Linux question :)

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