Strange problems with modems & routers

Unanswered Question
Sep 16th, 2007
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Hi,


I have a pair of 2522's with serial modems connected to the ports, and remote sites that dial in. They are to be replaced by 2821's but I am seeing some strange behaviour.


When I plug the modems into the 2821s, the ports come up as (looped), and constantly see interface resets. This can be resolved by applying "no physical-layer async" to the port, which clears the configuration, and then upon repasting the configuration in, the port works. The other end can dial in fine. Without performing no phys async, the receiving modem hangs up near-instantly, or directly after hand-shaking.


Does anyone have any idea what may be causing this?


Cheers,

Chris.

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aghaznavi Fri, 09/21/2007 - 09:45
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When you issue the physical-layer async command on the serial interface, a TTY line is assigned to the serial interface. This TTY line definition is where the databits, stopbits, parity, and speed are configured. The formula for determining which line corresponds to which serial interface is shown below.


line#=(slot# x 32) + interface# + 1



cpollock000 Sun, 09/23/2007 - 16:16
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Hmm I see, very interesting. Can I issue AT commands to the modem using this TTY line?


I'm still confused as to what happens at boot time though. The router boots up with the config on the interfaces, we can't successfully dial in. After "no phys async" the config is wiped, then paste in the original interface config and it works.


Any ideas? This is the main thing that is holding back the deployment, the fact that manual intervention is required to get it working after a reboot.

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