[cisco-nas] "show modem" output

[Aaron Leonard]

Clara Hatem wrote:

> Hello,
>
> We have a Cisco AS5300, IOS 12.1(5)T19, modem firmware 
> mica-modem-pw.2.9.5.0.bin, that is used to receive calls.
>
[ ... ]

> 2) Other modems are showing the following:
>
> Avg Hold Inc calls Out calls Busied Failed No Succ
>
> Mdm Time Succ Fail Succ Fail Out Dial Answer Pct.
>
> 1/16 00:16:40 182 21 0 0 0 0 1 90%
>
> * 1/17 00:18:54 175 14 0 0 0 0 2 93%
>
> * 1/18 00:17:58 176 21 0 0 0 0 3 89%
>
> 1/19 00:23:40 153 19 0 0 0 0 2 89%
>
> I wonder for example for 1/16, there are 182 success calls and 21 
> failed, out of which 1 is no answer.
>
> - What could the reasons for the remaining 20 failed connections be?
>
> - What are the common reasons for “No Answer”?
>
When an incoming call is switched to a modem, if the
call should clear before the modem goes offhook (begins
training), then this will be counted as a "no answer"
(which is a subset of "fail" I believe. Normally you
will have a window of maybe 1 second between the modem
getting the call and going offhook, but normally it is
rare that an originate modem will choose to go onhook
at that point - so normally you would see on the order
of 0.1% no answers. Your no answers seem to be a bit high
... one common reason for this is sloppy CAS (T1 RBS
or especially R2) where the transition in the DS0 between
call setup (i.e. inband tone) and talk path is somewhat
messed up.

As far as the 10% or whatever of calls that fail to train ...
it is normal to have something on the order of 4 to 10%
of modem calls not train ... due to noise in circuits,
channel impairments, erratic-behaving client modems, and
the general cussedness of things. 10% is on the high side
(although is not out of line for R2 deployments.)

Here are some articles that may be of interest:

Overview of General Modem and NAS Line Quality
http://www.cisco.com/en/US/tech/tk801/tk36/technologies_tech_note09186a008009478d.shtml

Troubleshooting Modems 
http://www.cisco.com/en/US/tech/tk801/tk36/technologies_tech_note09186a0080094eb9.shtml

Cheers,

Aaron