'Carrier Dropped' modem state hung problem

Question

Hello
We have Cisco 3660 (IOS 12.2(7)) as a dial-up router and a pool of different modems, including Zyxel U-336E Plus (1.0.8), Zyxel Omni Neo v.92, USRobotics Courier. Lines are configured like this:
line 85 86
no motd-banner
no exec-banner
no activation-character
modem InOut
modem autoconfigure type u336ep
no exec
transport preferred none
transport input all
escape-character NONE
autoselect ppp
autohangup
stopbits 1
speed 57600
flowcontrol hardware
The problem occurs on every line, despite of type of modem attached. After some time of operation (very soon, indeed, within 2 or 3 calls to the line) we get following:
# s lin 86
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
I 86 TTY 57600/57600 - inout - - - 238 571 0/4 -
Idle, Carrier Dropped
Line 86, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 57600/57600, no parity, 1 stopbits, 8 databits
Status: No Exit Banner, CTS Raised
Capabilities: EXEC Suppressed, Hardware Flowcontrol In,
Hardware Flowcontrol Out, Modem Callout, Modem RI is CD,
Line usable as async interface, Hangup on Last Close, No login banner
Modem Autoconfigure, MOTD Banner Suppressed
Modem state: Carrier Dropped
Modem hardware state: CTS noDSR DTR RTS
Special Chars: Escape Hold Stop Start Disconnect Activation
none none - - none any
Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch
00:10:00 never none not set
Idle Session Disconnect Warning
never
Login-sequence User Response
00:00:30
Autoselect Initial Wait
not set
Modem type is u336ep.
Session limit is not set.
Time since activation: 00:08:14
Editing is enabled.
History is enabled, history size is 10.
DNS resolution in show commands is enabled
Full user help is disabled
Allowed input transports are pad v120 lapb-ta telnet rlogin.
Allowed output transports are pad v120 lapb-ta telnet rlogin.
Preferred transport is none.
No output characters are padded
No special data dispatching characters
Line remains in this state until 'modem InOut' command issued for this line, or router reloaded. Modem on the line answers normally and passes handshake, but the line protocol remains down.
Can anyone advise anything to fix this?
Thanks in advance

Answer 1

Since there has been no response to your post, it appears to be either too complex or too rare an issue for other forum members to assist you. If you don't get a suitable response to your post, you may wish to review our resources at the online Technical Assistance Center (http://www.cisco.com/tac) or speak with a TAC engineer. You can open a TAC case online at http://www.cisco.com/tac/caseopen
If anyone else in the forum has some advice, please reply to this thread.
Thank you for posting.