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ZyXEL modem FAQ List v4.2, Nov 20 1995, Part 3 of 5 [Technical FAQs]
Section - T.8 What is the meaning of the T401 and T402 timeouts seen in an "AT I2"?

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Top Document: ZyXEL modem FAQ List v4.2, Nov 20 1995, Part 3 of 5 [Technical FAQs]
Previous Document: T.7A What is the advantage of this design?
Next Document: T.9 What is the selective reject in V.42?
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On page 15-13 of the ZyXEL User's Manual (Revision 2.1), [page 15-6 in the 
on-line version] it says that the T401 and T402 timeouts "are normally zero".

Often these values are not zero.

T401 and T402 are the name for two timers that are used in MNP 4 and V.42 
connections.  The values for both timers are set during the initial handshake.
The T401 is the acknowledgement delay timer that monitors the amount of time 
between the sending of a data block and the receiving of an acknowledgement.
The T402 is an inactivity timer which monitors the time between data blocks 
sent to the receiver.

The terms "T401 Timeout" and "T402 Timeout" refer to the number of timeouts
in the T401 and the T402 timers, respectively.  (A timeout is a "timer 
expiration" and is the result of an action not being performed in a given 
allotted time.)

Brent Mosbrook (brentm@zyxel.com) [ZyXEL USA] writes:
The "T401 Timeout" indicates the number of resent blocks, due to not 
receiving an acknowledgement in the allotted time.  The T401 timeout is 
just one of the reasons for blocks being resent, so T401 timeouts will not 
necessarily be equal to the BLOCKS RESENT value in a link status report.

The "T402 Timeout" indicates the number of frames sent due to inactivity.
These are sent to keep the link active, and assures the other modem that
the connection is still there.  This number steadily increases, especially 
during a relatively "light" interactive dialup session.


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Top Document: ZyXEL modem FAQ List v4.2, Nov 20 1995, Part 3 of 5 [Technical FAQs]
Previous Document: T.7A What is the advantage of this design?
Next Document: T.9 What is the selective reject in V.42?

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