Call forwarding to mobile and SMS notification in the absence of a response. One of the possible implementations of a “callback”

Good day to all!

In this article I want to describe my version of the implementation of some functionality implemented on my Asterisk server.

It describes:
- an option for implementing call forwarding to mobile using a two-channel SIP-GSM gateway and a multi-channel Multifon;
- SMS-notification of the subscriber through the free email2sms service;
- implementation of a “direct” entry into the general internal numbering plan for a mobile subscriber using software (for Android) and hardware (SIM-Dialer for ordinary mobile phones) methods.

Details under the cut.

I do not pretend to be ideal for the community code, I post it “as is”. I will be glad if my work is useful to anyone.

In our organization, the departmental telephone network is mainly built on Si2000 and only we use the DX-500.



To interface “my” IP server with “my” PBX (DX-500), Quasar-M (PCI bus) is used per PRI E1 stream. The internal numbering within the enterprise is predominantly five-digit: 2xxxx - 5xxxx. In "my" branch (on my DX-500) numbers 54xxx are allocated and used. The entire 55xxx segment goes to Asterisk.



Forwarding subscribers set and remove themselves -112 55xxx (service code DX-500). The numbering is transparent - the number 54705 on the DX corresponds to 55705 on the Asterisk.



Asterisk, receiving from the E1 stream incoming to a “virtual” number of the form 55xxx, checks its transfer base and, if available, makes an outgoing call to the appropriate mobile.



My system uses an “iron” GSM-gateway - channels 1 and 2, the multi-phone account is bolted to channel number 3.

Outgoing calls go through a free channel. Priorities are given by the conditions in dialplan 1-> 2-> 3. A separate GSM-Channels database has been created - in it I sometimes turn off a channel as needed.

Channel 3 is a “multi-channel” multiphone, limited only by the call-limit option in sip.conf.

Alas, through GSM-gateways and a multi-phone, we can not replace CallerID and the subscriber sees the incoming from the SIM card number installed in the gateway - he does not know who is calling him. If it does not answer (or forcibly rejects an incoming call), an SMS notification with the caller's number (and the time of the call) is sent to the subscriber.

Our Asterisk sends a specially formed e-mail letter to the mailbox of the mobile subscriber. As a result, the mobile subscriber receives the text of the letter in the form of SMS. The implemented function is completely free and works without noticeable delays.

Personally, it’s very expensive for me to send regular SMSs from a GSM modem, but maybe with a connected SMS package someone decides to do just that in order to isolate Asteriska from “external influences”.





Move on.

For the complete rejection of the deployed IT solution - DECT tubes (and base stations located on the industrial site), as from an outdated atavism, something else has been done.



“My” mobile subscribers are divided into two conditional categories according to their equipment: Android users and users of ordinary ancient mobile phones (usually an age guide). All of them use the corporate tariff, where all intra-company calls are free / unlimited.
Thanks to its multi-channel nature, a multi-account account works great for incoming calls.



Android users use the Prefixer application (you will find in the market - not advertising). For outgoing to the internal departmental network at the usual numbers, one rule is enough:

When number matches - [2-5]. * - the rule processes all numbers starting with 2,3,4,5.
Add prefix: 8922xxxXXxx ,,, - Asterisk server multifonovy account, three commas - this is a pause three seconds after the connection (at this time, Asterisk server DISA happily greets the caller).

Thus, when a mobile subscriber dials the number 54705 familiar to him on his mobile phone, the application intercepts the call control, dials the prefix defined in the rule (multi-phone account number), waits a pause of three seconds to skip the voice greeting, and dials the numbers 5 4 7 0 5 into the channel using the DTMF.

In the near future I will correct the DISA dialplan to check the CallerID of an incoming call in the transfer database - why not listen to a voice greeting every time and ask to dial an extension number to subscribers who have Prefixer configured - let the number be dialed right away.

The second category of subscribers, for some reason, still uses ordinary mobile phones. For them, interesting devices were ordered from China - SIM-Dialer. They represent a sort of “lining” for the SIM card, they are configured absolutely simply and provide functionality similar to Prefixer. The issue price at the time of ordering is 4.5-5 USD per unit.

Thus, my mobile subscribers have convenient (for themselves) and free (for the enterprise budget) calls to the internal corporate network.

Continuation of the article ...
There was a need to remove voice instructions when calling a DISA number (mobile) for "ours". In principle, for those who need to, you can weed out incoming calls from "foreign" numbers. Details under the spoiler. Welcome!



I don’t think that this code is tricky or original, but it can probably come in handy for someone ... Moreover, this is a logical continuation of the functionality described above.