Integrating calls via GSM in Asterisk

Technical specification (TS) for integrating calls via GSM in Asterisk using Python

1. General information

The goal of the project is to develop a system that allows making calls to subscribers through the GSM network with minimal delay, using Asterisk as the main server solution. Calls will be initiated from Python scripts integrated with Asterisk. The system should choose between GSM and SIP depending on availability and network quality.

2. Functional requirements

2.1. Integration with GSM via Asterisk

• Configure GSM gateway to work with SIM cards through Asterisk.
• Ensure the ability to make and receive calls through SIM cards installed in the GSM gateway.
• Set up trunks for communication between Asterisk and the GSM gateway with minimal delay.
• Configure the ability to route calls through the GSM network for specific subscribers.

3. Technical requirements

3.1. GSM gateway

• Equipment: GSM gateway (e.g., GoIP, OpenVox, or Yeastar).
• Support for multiple SIM cards for simultaneous calls.
• Support for SIP standard for interaction with Asterisk.

3.2. Asterisk

• Version: Asterisk 16 or higher
• Configuration of sip.conf, extensions.conf.

3.3. Python

• Use of a library for working with AMI/AGI, such as pyst2 (for AMI) or custom HTTP requests to AMI.
• Ability to initiate a call based on specified parameters (subscriber number, network type).
• Logging of all calls with time, status, and selected network.

4. Use cases

4.1. Outgoing call via GSM

1. The Python script receives a request for an outgoing call.
2. Checks the availability of the GSM gateway.
3. Initiates the call via GSM if the connection is stable.
4. Sends the call status and logs it.

4.3. Network selection for outgoing call

1. The Python script receives a request for an outgoing call.
2. Checks the status of both networks (GSM and SIP).
3. Initiates the call through the network with the least delay or specified priority.

5. Non-functional requirements

5.1. Performance

• The time to initiate a call should be minimal: less than 2 seconds for GSM and less than 3 seconds for SIP.

5.2. Reliability

• Calls should be routed through an alternative network if the primary is unavailable.

5.3. Logging

• Logs of each call should be saved with the indication of:
  • Time of initiation.
  • Subscriber number.
  • Network used (GSM/SIP).
  • Call status (successful/failed).

6. Interfaces and interactions

• Interaction of Python scripts with Asterisk will occur via AMI or AGI.
• Interaction with Asterisk will be carried out through a local area network (LAN) or the internet, depending on system settings.

9. Support and maintenance

• After implementation, the system should support the possibility of further expansion and integration with new networks and providers.