> For the complete documentation index, see [llms.txt](https://learn.doubletick.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learn.doubletick.io/additonal-channels/pstn-voice-call/pstn-voice-calling-guide.md).
# PSTN voice calling guide
Learn how to use DoubleTick Telephony to make PSTN calls from DoubleTick, plan the channels you need, and fetch AI call summaries through the public API.
DoubleTick Telephony lets you make PSTN calls, which are regular phone calls, directly from DoubleTick using channels provided by TATA. This article covers how a PSTN call works, what's included with PSTN calling, the KYC documents needed, how channels and concurrency work, and the two ways to make PSTN calls.
#### What's covered
* [How a PSTN call works](#how-a-pstn-call-works)
* [Everything that is included](#everything-that-is-included)
* [Documents required for TATA KYC](#documents-required-for-tata-kyc)
* [Understanding channels and DID](#understanding-channels-and-did)
* [How many channels are needed](#how-many-channels-are-needed)
* [Two ways to make PSTN calls](#two-ways-to-make-pstn-calls)
* [Key takeaways](#key-takeaways)
* [Frequently asked questions](#frequently-asked-questions)
* [Related articles](#related-articles)
#### How a PSTN call works
Each call uses 2 channels. One connects to the agent's phone and the other connects to the end user, and both merge into a single conversation.
* The agent starts the call from DoubleTick.
* Channel 1 rings the agent's phone.
* The agent picks up.
* Channel 2 rings the end user.
* Both channels merge, and the agent and end user speak.
* When the call ends, both channels are released.
PSTN numbers can also be onboarded on WhatsApp Cloud API. During onboarding, the OTP must be triggered via a phone call, since SMS does not work on PSTN numbers.
#### Everything that is included
Once PSTN calling is enabled for a customer, here is what they get:
* **Mobile support**: Click-to-Call works on mobile, so agents don't need to be on a desktop to make calls.
* **CRM integration**: PSTN calling works inside Salesforce and other custom CRMs, so agents can make calls without leaving their CRM.
* **Call recordings**: Every call is recorded. The recording is saved automatically inside the WhatsApp chat of that contact and is also visible in the Calls section of DoubleTick. This comes at an additional cost of 0.02 per minute, deducted from the wallet.
* **Transcription and summary**: Calls can be automatically transcribed and summarized, which is useful for managers who want to review calls without listening to the full recording.
* **Call summary via public API (****New****)**: You can fetch the AI-generated summary of any completed PSTN call using its **call ID** with `GET /v1/call/ai-summary?callId=`. This works for both AI-bot and human-agent calls, inbound and outbound, and returns a recap, key points, and next steps. See the [**PSTN Call AI Summary API reference**](https://docs.doubletick.io/reference/get-pstn-call-ai-summary) for the full request and response details.
* **Call analytics**: Call metrics like talk time, number of calls, and missed calls will be available inside Enterprise Analytics. This is currently being rolled out in the next 2 weeks.
* **AI calling**: AI-powered calls work on PSTN as well, so you can run automated AI calling campaigns through DoubleTick, not just on WhatsApp.
* **Call routing**: Inbound call routing is managed through the Inbound Call Trigger inside Bot Builder. Inbound call routing via Bot Builder is in the pipeline and not yet available.
* **Multi-user support**: Multiple agents can be mapped to a single PSTN channel, just like multiple agents work on a single WhatsApp number.
* **Deactivation**: A Deactivate button is available to turn off a PSTN channel. A Delete button is coming soon.
#### Documents required for TATA KYC
Collect all of the following from the customer before starting the procurement process:
* Incorporation Certificate or MSME Gumastha
* GST Certificate
* Company PAN Card
* Signatory person's ID proof, email ID, and contact number
* Authorization Letter or BOR, required only if the company Director is not signing the documents
* Company address proof
* Aadhaar Card, for KYC verification
{% hint style="warning" %}
**Note on Aadhaar**: One Aadhaar card can be used to set up a maximum of 5 TATA channels. If more than 5 channels are needed, you need one additional Aadhaar card for every 5 channels.
{% endhint %}
#### Understanding channels and DID
A **channel** is a single phone line that handles one call connection. Every call needs 2 channels, one for each side.
A **DID number** (Direct Inward Dialing) is the actual phone number assigned to your channels. This is the number customers see on caller ID.
Here's how it works:
* The client purchases channels from TATA.
* TATA deploys all channels on DoubleTick's AWS.
* Half the channels are onboarded on DoubleTick for the agent side, and the other half stay on DoubleTick's AWS for the end user side.
* For example, if 10 channels are purchased, 5 are onboarded on DoubleTick for agents and 5 stay on AWS for end user connections.
TATA only sells channels in multiples of 10 (10, 20, 30, and so on), so you cannot buy 12, 15, or 26 channels.
#### How many channels are needed
Concurrency is the number of agents on active calls at the same time. To work out the channels needed, multiply the number of agents on calls at the same time by 2, then round up to the nearest multiple of 10.
| Agents on calls | Channels needed | Purchase (multiple of 10) |
| --------------- | --------------- | ------------------------- |
| 3 | 6 | 10 |
| 5 | 10 | 10 |
| 8 | 16 | 20 |
| 15 | 30 | 30 |
| 22 | 44 | 50 |
This is based on peak concurrency, which is the maximum number of agents on calls at the same moment, not the total team size. For example, a team of 20 agents with only 5 on calls at once needs 10 channels, not 40.
With too few channels, calls will fail during peak hours. With too many, you pay an unnecessary fixed cost.
#### Two ways to make PSTN calls
* **Direct calling from chats**: An agent calls a customer one-on-one from the Chats section. Channel 1 rings the agent, channel 2 rings the customer, and both merge. This is billed at ₹0.60/min from the DoubleTick wallet.
* **PSTN voice campaigns**: Bulk calling from a list, where the system dials automatically. Both the PSTN cost (₹0.60/min) and the AI cost (10 AI credits/min) apply.
| | Direct calling | Voice campaigns |
| --------- | -------------------------- | --------------------- |
| Use case | One-on-one calls | Bulk outreach |
| Who dials | Agent | System (automated) |
| Billing | ₹0.60/min (+ ₹5/min if AI) | ₹0.60/min + ₹5/min AI |
#### Key takeaways
* DoubleTick Telephony lets you make regular phone calls from DoubleTick using TATA channels, and every call uses 2 channels.
* PSTN calling includes call recordings, transcription and summary, AI calling, and multi-user support.
* You can fetch the AI summary of any completed PSTN call through the public API using its call ID.
* Plan channels based on peak concurrency, and purchase them in multiples of 10.
* One Aadhaar card covers a maximum of 5 TATA channels.
#### Frequently asked questions
How do I fetch the AI summary of a PSTN call?
Use `GET /v1/call/ai-summary?callId=` with the call ID of a completed PSTN call. See the PSTN Call AI Summary API reference for the full request and response details.
Which PSTN calls does the AI summary API support?
It supports completed AI-bot and human-agent calls, both inbound and outbound.
What does the PSTN call AI summary include?
Each summary includes a recap of the call, the key points discussed, and the next steps.
How many channels are needed for PSTN calling?
Multiply the number of agents on calls at the same time by 2, then round up to the nearest multiple of 10. For example, 8 agents on calls at once need 16 channels, so you purchase 20.
Can any number of channels be purchased?
No. TATA only sells channels in multiples of 10, such as 10, 20, or 30.
Can a PSTN number also be onboarded on WhatsApp Cloud API?
Yes. During onboarding, the OTP must be triggered via a phone call, since SMS does not work on PSTN numbers.
How many TATA channels can one Aadhaar card be used for?
One Aadhaar card can be used for a maximum of 5 TATA channels. You need one additional Aadhaar card for every 5 extra channels.
#### Related articles
{% content-ref url="/spaces/53n17VnOICC1LtDqlENV/pages/dvIgdcxOK5mU3A7dAj0V" %}
[How to Onboard a PSTN Number on DoubleTick](/additonal-channels/pstn-voice-call/how-to-onboard-a-pstn-number-on-doubletick.md)
{% endcontent-ref %}
{% content-ref url="/spaces/53n17VnOICC1LtDqlENV/pages/Wlqb3KFkUX4I814DhZ02" %}
[How to Edit Your PSTN Channel and Manage Agent Access](/additonal-channels/pstn-voice-call/how-to-edit-your-pstn-channel-and-manage-agent-access.md)
{% endcontent-ref %}
{% content-ref url="/spaces/53n17VnOICC1LtDqlENV/pages/iIHDVaOQqnApshIlz1uL" %}
[How to place an outbound PSTN call](/additonal-channels/pstn-voice-call/how-to-place-an-outbound-pstn-call.md)
{% endcontent-ref %}
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