I wanted to send a reply to this post, but I am glad I was
delayed. Howard's post was so much more relevant in terms of
depth and historical understanding. There was one particular
area I did want to comment on. Modem configuration tends to
give a little bit of confusion, namely the concept of
autoconfigure. Let me try to simplify it as follows.
Let's say you had a single modem hung off your router. You are
a competent person and you can read the data plate on the
modem. It says, "USR Sportster V.90". This is a job for the
following command:
router(config)#line 1
router(config-line)#modem autoconfigure type usr_sportster
router(config)#end
router#
**Note- other commands will be needed, just focusing on this
one area/issue.
What this will do is set up the attached modem to be configured
each time the line is reset to the defaults for a USR
Sportster. These values can be obtained using the "show
modemcap usr_sporster" command. As an example, here are some of
the settings:
werner-gateway#sh modemcap usr_sportster
Modemcap values for usr_sportster
Factory Defaults (FD): &F
Autoanswer (AA): S0=1
Carrier detect (CD): &C1
Drop with DTR (DTR): &D2
Hardware Flowcontrol (HFL): &H1&R2
Lock DTE speed (SPD): &B1
DTE locking speed (DTE): [not set]
Best Error Control (BER): &M4
Best Compression (BCP): &K1
No Error Control (NER): &M0
No Compression (NCP): &K0
No Echo (NEC): E0
No Result Codes (NRS): Q1
Software Flowcontrol (SFL): [not set]
Caller ID (CID): [not set]
On-hook (ONH): H0
Off-hook (OFH): H1
Miscellaneous (MSC): [not set]
Template entry (TPL): usr_courier
Modem entry is built-in.
If you want to modify these default settings, you will need to
build a custom modemcap entry of your own and template off one
of the established entries. For example, if I liked the entry
above, but wanted to change to another value(let's say for
compression), I could make a new entry called, "my_sportster"
and just change the compression value and template the rest
from the sporster entry shown above.
This is drastically contrasted with the "modem autoconfigure
discovery" command. First, let me explain how it works. Once
the modem gets reset, it goes through a series of language
classes. The router starts talking French to the modem and
says, "Parlez vous Francais?" If it gets no reply, it tries
this, "Habla Espanol?" obviously, they are talking modem
speak, and the question is not which language do you speak, but
rather what command will you respond to? When the modem
answers back in a postive manner to a series of queries, the
router assumes it to be an "X modem", whatever value that is.
Sometimes it's right, and sometimes it isn't. Your mileage
will vary. The next question that comes to mind is why use
this? The answer is as always, it depends. Let's say you
don't know what modem is attached. This command might help.
Another place where this might come in handy is if you are
configuring an access server with lots of different modems
attached (not a good practice BTW:-). In theory, let "modem
autoconfigure discovery" loose, and it should nail down who is
what. Here is the key to using this effectively. Once "modem
autoconfigure discovery" is done polling all of the modems, it
will tell you what it *believes* are the individual modems
attached to all of your lines. At that point, you want to hard
code the config with the "modem autoconfigure type
usr_sportster" command, or a similar command for your brand of
modem. If you don't do this, you will dramatically increase
the time it takes to get your modem active after each reset.
HTH,
Paul Werner
p.s. I particularly like Priscilla's explanation of why things
are/are not in the IOS. I would have to default to the wise
one (Tim Brown) and state that in many/most cases, it is
probably just a matter of original sin 8-)
> > > First, I understand the theoretical difference
between
> >Autoconfigure
> > >and Autodiscovery, but in the book, it appears that the
different
> >commands
> > >do the same thing. For Autoconfigure, the book says "The
modem
> >autoconfigure
> > >command is used to instruct the router to use this
feature. This
> feature
> > >will detect the type of modem connected to the router and
then supply
> the
> > >initialization string to the modem-- a process that can
require up to
>
> >five
> > >seconds."
> > > It sounds as if the modem autoconfigure command also
performs
> > >autodiscovery functions. Did they really mean to say that
the command
> is
> > >modem autoconfigure modem_type ?
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