Re: (ASCEND) Ticket #802135 - Disconnect Problems on 4048 with 7.0.1

[Jason Nealis <nealis@babylon.erols.com>]

The problem of 185's withn our network have gotten significantly 
worse overtime. I use to see around 10-12% of 185's and now I'm
getting up to 20% of 185's. There is a modem corruption issue happening
here and it's affecting the quality of the calls. 

Also you can look at the progress code of the 185's to break them
down even further.

Jason Nealis
Director Internet Operations / Network Access
Erols Internet (An RCN Company)




> >> 185  -  Remote End hung up - signal lost form far end
> 
> Exactly what it says ... for reasons the Max does not know,
> the connection with the remote modem was lost.
> 
> Indeed you can cause this fairly easily:  just establish
> a connection and then disconnect the remote modem
> from the telephone line.
> 
> >From our research, we feel the 185 disconnect can
> be attributed from the following:
> 
> - phone line quality degradation
> 
> We've experimented with a number of "bad" telephone
> lines - including some that would not even establish a
> v.90 session.  Using some USR modems that keep
> track of statistics we looked at the stats after an
> abnormal disconnect ... often finding a lot of modem
> retrains, and typically disconnects from the modem
> due to its inability to successfully retrain.  In other words,
> when a modem finds the line quality degrades beyond
> a certain threshold, it attempts to "retrain" (almost like
> the initial connection effort).  This retrain can be seen
> as a period of inactivity - sometimes between 30 and
> 60 seconds.  Sometimes the modem can continue
> where it left off, and other times it can't, in which case
> it disconnects (hangs up).  Max gets 185 disconnect.
> 
> - human problem
> 
> User disconnects modem from phone line, disconnects
> power from external modem (effectively hanging up modem!),
> engages (picks up) a telephone that is also on the same
> line as the modem whilst it is connected, phone company
> technician "taping" or working on wires, etc.
> 
> - implementation problems
> 
> A good implementation of the PPP protocol will send
> a disconnect to the Max and then take down the connection.
> But a poor implemenation may work as follows:
>  - queue up the disconnect message
>  - before the message is successfully sent,
>    cause the modem to be disconnected
>    usually via negotiation of the modem control signals
>    (like DTR, etc.)
> 
> 
> I'm sure there's other reasons for the 185's,
> but as you can see - there's really no way that the Max
> can know or tell you which one it may be, or why.
> You can only ascertain that by careful analysis
> of the radius logs ... and possibly radius server
> status messages (like the Ascend Access Control's)
> based on detailed (and accurate) feedback from
> the remote user.
> 
> Hope this helps.
> Bob McCormick
> 
> 
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