gramels blog

Here another (german) example of VoIP SPAM.

"Sie haben gewonnen!"

spit-preis-gewonnen.mp3

Da sich eine Menge alter Telefonnummern in meiner Telefonanlage ansammeln, führt dies auch zu VoIP SPAM, hier ein Beispiel:

Since I have a bunch of old phone numbers hooked to my pbx it catches SPIT from time to time. Here is the first one:

umfrage-spit.mp3

german, survey about economic situation in germany, voice computer

intro

This howto is a extension to my recent "simple (fixed) asterisk callback configuration". This configuration is useful to trigger a callback from a location you rarely use, but provides a callerID. This is for example useful in hotel rooms for one night, phone cells, friends homes. The call process is the following:

1. you call from a phone with callerID 004144555111 the trigger number 004144555666
2. wait for the busy signal
3. hangup
4. wait until the phone rings
5. enter password
6. enter target number

The target number will then be called according to the outbound call routing in your pbx.

1. The system recognizes rejects all calls on the trigger number.
2. It uses the callerID and generates a temporary call file which will will be copied from a directory (/var/spool/asterisk/ in the example below) into the outgoing directory
3. asterisk initiates the outbound call according to the rules in the call file
4. once you pick up the callback call, you will get a dialtone and be able to dial as from a local extension

intro

This a simple howto get a callback feature into asterisk.

Its based on the assumption, that you have a account at a provider, which lets you dial into your box remotely and the location you call from provides a callerID. So this setup is mostly useful, if you have a flatrate at home and would like to use it, lets say, from your parents place.

The call process looks is the following:

1. you call from the phone which sends the caller ID 004144555111 the trigger number 004144555666
2. wait until you get a buisy signal
3. hangup
4. wait until it rings
5. pick it up
6. enter password (optional, see security remark)
7. enter target number

Of course, you can setup more than one of those in case you are in a hotel and your room fone provides direct dial through callerID. Just install it temporarily for your hotel stay on your home asterisk.

Security remark: The authentication of the callback trigger is based on the callerID of the calling line. If your SIP provider allows SIP URI calls the callerID might be spoofed. I thats the case, you should but additional security in place (like a password, see below).

A more complicated setup which allows to trigger a callback from any number can be found here.

how does it work

1. The system recognizes the number you dialed and the number you dialed from (CallerID)
2. the call gets rejected
3. a fixed call file will be copied from a directory (/var/spool/asterisk/ in the example below) into the outgoing directory
4. asterisk initiates the outbound call according to the rules in the call file
5. once you pick up the callback call, you will get a dialtone and be able to dial as from a local extension

example