Super flexible, custom voice mail and call routing for Twilio controlled by a Telegram bot control interface.
- Routing of incoming calls based upon a flexible, wildcard enabled routing table
- Voicemail
- Transcription of voicemail messages using Google speech to text
- Recordings are delivered using a Telegram bot
- Voicemail and routing are controlled through a Telegram bot
- Supports multiple inbound/outbound numbers
Voice control is build on Spring Boot and Java 11. Telegram API calls are handled by an open source library. MongoDB is used as the document store for call information and voice mail message metadata. Audio files are stored on hard drive.
Twilio is used as the PSTN routing solution and programmable voice provider. Google Cloud Platform speech to text is used for transcribing voicemail messages.
The user interface is text based over a Telegram chat bot.
Inbound calls are routed based upon a routing table stored in MongoDB. If none of the rules match then the defaults, set in the application.properties file are used.
The routing table for inbound calls, has the following structure:
| From | To | Action | Destination | Priority |
|---|---|---|---|---|
| +43* | * | FORWARD | +43123412345 | 100 |
| +49676* | * | REJECT | 90 | |
| +44 | +1 | FORWARD | +431268686868 | 80 |
The wildcards * and ? are matched in the From and To fields. Priority is used to order the routing table entries, where a higher priority means that this entry will be tested and matched first.
This also means that entries which are more specific will be shadowed by less specific entries.
In the following example the second rule will never be applied, since the first routing rule already matches.
| From | To | Action | Destination | Priority |
|---|---|---|---|---|
| +43* | * | FORWARD | +43123412345 | 100 |
| +43123* | * | REJECT | 90 | |
| +44 | +1 | FORWARD | +431268686868 | 80 |
Therefore more specific rules need to have a higher priority then less specific rules.
Number availability is also managed by the InboundCallRoutingService. The availability of the numbers is stored in the database.
Routing is performed first, and then the availability of the number to which the route leads is checked. If this number is currently unavailable the action will be changed from FORWARD to SEND_TO_VOICEMAIL.
Google Cloud Platforms speech to text API is used for transcribing voicemail messages. The API is used in async, enhanced mode, with the default model and automated language detection.
The endpoints for twilio are protected by a ServletFilter. All Twilio requests are signed using a HMAC signature , this signature is verified in the filter and a 403 - FORBIDDEN is returned if the signature is missing or invalid.