Scenario 5: Bad Modem

A bad modem is not something generally reported by your clients . A modem that is experiencing problems usually does not mark itself as defective unless there is an obvious hardware problem. Instead, you must analyze the modem with the show modem command.

An output from show modem is provided in Example 8-7, where a group of six modems are obviously bad. In the AS5300 access server, modems generally become faulty in groups of six or 12, depending on the types of modems in the device.

Example 8-7. Output of show modem Showing a Bad Modem Card

 Avg Hold     Inc calls     Out calls    Busied   Failed    No     Succ   Mdm     Time      Succ   Fail   Succ   Fail    Out      Dial   Answer   Pct. * 1/0   00:57:37     408      7      0      0       0        0       0     98% * 1/1   01:02:03     397      8      0      0       0        0       0     98% * 1/2   01:08:09     374      8      0      0       0        0       0     98% * 1/3   00:52:28     419      7      0      0       0        0       0     98% * 1/4   00:48:24     434      8      0      0       0        0       0     98% * 1/5   00:57:55     417      5      0      0       0        0       0     99% <output omitted> * 1/30  01:04:09     350     36      0      0       0        0      30     91% * 1/31  00:46:53     409     41      0      0       0        0      30     91% * 1/32  00:53:40     366     43      0      0       0        0      30     89% * 1/33  00:53:00     384     37      0      0       0        0      29     91% * 1/34  00:48:18     393     38      0      0       0        0      30     91% * 1/35  00:58:22     362     39      0      0       0        0      30     90% 

The first six modems perform as they are supposed to. There are always a few bad calls because of people dialing the number with a telephone, calls cancelled after they have been placed, or other user initiated errors. However, when a group of modems in sequence (in groups of six with Modem ISDN channel aggregation [MICA]) are all showing a much higher number of failed incoming calls, the modems are not working properly.

What is of interest in determining a bad modem can be seen in the next group of six. The call success ratio dropped eight to ten percent below that of the good modems. Also, these modems have not answered some calls, as noted by the column labeled No Answer. These modems likely became faulty recently because the output shows that they also have received many successful calls. Approximately the last 30 calls were answered by each modem, but not connected, which forced the customer to place the call again.

To fix this problem, these modems must be replaced. For companies that have a scheduled maintenance period, you can mark the modems as bad until the defective hex modem modules are replaced . To mark the modem as bad, use the line configuration command modem bad . This stops any future calls from being accepted on these modems:

 5300-dialin(config)#  line 31 36  5300-dialin(config-line)#  modem bad