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8. msn: Configuration/MSNs

8.1 msn_my1: What is my MSN? What if I don't have any?

Your telephone company will tell you your MSN. It is your own telephone number. Please note that you have to provide i4l with at least one MSN. If you don't have any you can use `0', which is assumed if no MSN is transmitted from your telephone company. Check section countries, together with the following questions, on how to configure your MSN(s).

8.2 msn_my2: How can I find out how my telephone number is transmitted to the calling party?

The transmitted MSN can simply be determined by calling yourself (for example by telephone). In the log files you will find the entry that looks like: "isdn_tty: call from XXX - YYY ignored" (in order for this to work, you must of course already have the ISDN drivers in your kernel and active).

8.3 msn_config: How do I configure my MSN?

If your telephone number were 56789, then it would be configured as follows:

You may find national differences here (check section countries).

8.4 msn_max: How many MSNs as a maximum can I use for an isdn card?

For outgoing calls, at maximum one MSN can be used. Only incoming calls may be configured to allow multiple MSNs.

For ttyI* devices, at a maximum you can listen to EVERY incoming MSN by using the * as a wildcard:


When you have a point-to-point connection you should rather specify the length of your number area with as many times "?" as you have digits, otherwise your number may be accepted too early on overlapping receiving. I.e. for 3 digits use:


For network devices, you can also use a '*' as a wildcard at the end of the number for incoming calls (e.g. isdnctrl msn interface 123*). However, this will create problems for outgoing calls. To handle such a situation properly, please use the isdnctrl mapping feature (see question dialout_manycards).

8.5 msn_mindialin: How can I minimize usage of MSNs for digital data dialin?

i4l gives priority to net interfaces. Therefore, you can get away with only one MSN when you set it up like this:

  1. Set up net interfaces (sync ppp, rawip) for all users that will want to use them (ipppd or rawip), with their incoming phone number (precondition is that it is transmitted).
  2. Set up ttyI* for all other users (X.75, async ppp).
  3. Set option `secure on'.
i4l gives priority to net interfaces. `secure on' ensures that only users that have been set up will be connected to a net interface. Users that want to choose between both will have to use different outgoing MSNs to call you.

8.6 msn_onlyone: How can I use one MSN for everything?

In Germany, this is not much of an issue any more since you can get 10 MSN for free with Deutsche Telekom ( Other phone providers may offer less MSN for free. In general, you can get at least 3 MSN. However, minimizing MSN usage may still be very interesting for other countries or if you have a large demand for numbers. On a normal ISDN bus with MSNs, 10 MSN per bus are the maximum. To get more numbers, your only alternative would be to get a usually more expensive point-to-point ISDN connection.

Digital data dialin can easily be distinguished from voice/analog modem dialin by the 'Service Recognition' code ("digital, data").

For the differentiation between net interfaces (ipppd, rawip) and ttyI* (X.75) see last question.

To get voice/analog modem to work in parallel, use mgetty for the analog modem. Mgetty can handle analog data calls, faxes, and even voice calls as answering machine if the modem supports it. Configure it for 10 rings. If you take the phone and hear a fax or modem, send mgetty a USR1 signal (kill -USR1 mgetty-pid). If your phone socket is correctly wired, the modem will take over the connection, cutting off the phone. If you have an ISDN PBX then you can forward the call to a different analog port when you picked up a fax/modem call.

If your analog modem can not handle voice calls, then you have to choose since incoming voice calls can not be distinguished from analog fax/data calls. Use either VBOX to take your voice calls as an answering machine. Or forget about voice calls and set up your modem to handle only faxes and/or analog data calls.

8.7 msn_buendel: Can I have several NTBAs, all with the same MSN?

Yes, but you need the cooperation of your telecommunication company. They can set up several BRIs in Point-to-point mode that have the same MSN. In Germany it is called a bundled line (`Bündelanschluß').

Please note that in such a case the MSN may not be transmitted to you. Just use the default MSN 0 then.

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