> ## Documentation Index
> Fetch the complete documentation index at: https://docs.poly.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Connecting to PolyAI Telephony
> Start routing phone calls into PolyAI.
Once you've created a [SIP Trunk](/api-reference/sip-trunking/introduction), you can start routing calls to it. Every inbound call must:
1. Reach a PolyAI SIP server.
2. Tell PolyAI **which trunk** it belongs to.
3. Satisfy the trunk's authentication, if you have configured any.
## Where to send calls
PolyAI provides both DNS A records and SRV records to route calls to PolyAI SIP servers.
### SIP Trunk A record (recommended)
Each SIP Trunk is issued a unique hostname, returned as `inbound.hostname`:
```
tr-0123456789abcdefghijklmn.sbc.sip.eu.poly.ai
```
This resolves to a **multi-A DNS record** listing all of the PolyAI SIP servers in the region. You can either:
* Treat each IP as a unique destination, and route calls evenly across each, or
* Use only the first A record to let PolyAI randomly balance calls across the destinations for you.
Because the trunk ID is embedded in the hostname, **no extra SIP header is needed** — PolyAI identifies the trunk from the host you connected to.
PolyAI recommends against DNS caching, to avoid routing traffic to any disabled SIP servers.
### Global A record
PolyAI also publishes a shared hostname per region:
| Region | Global A record |
| - | - |
| US | `sbc.sip.us.poly.ai` |
| EU | `sbc.sip.eu.poly.ai` |
| UK | `sbc.sip.uk.poly.ai` |
Returns the same multi-A record as the SIP Trunk A record, but can be used where your SIP server routes traffic to multiple PolyAI SIP Trunks or accounts. As the host is shared, you **must provide the SIP Trunk ID** on every `INVITE` (see [Identifying the SIP Trunk](#identifying-the-sip-trunk)).
### SRV records
If you'd rather discover the PolyAI servers via SRV, PolyAI publishes records using the same hostnames as the Global A records (`sbc.sip..poly.ai`). `` is one of `eu`, `uk`, `us`.
| Service | Protocol | Use for |
| - | - | - |
| `sips` | `tcp` | TCP/TLS SIP with SRTP media (encrypted trunks) |
| `sip` | `udp` | UDP SIP with RTP media (unencrypted trunks) |
When you connect via a Global A record or SRV, you **must provide the SIP Trunk ID** on every `INVITE` (see [Identifying the SIP Trunk](#identifying-the-sip-trunk)).
## Transport and encryption
PolyAI supports both encrypted and unencrypted transports.
| | Signaling | Media | PolyAI SIP port |
| - | - | - | - |
| encrypted | SIP over TCP/mTLS | SRTP over UDP | 5061 |
| unencrypted | SIP over UDP | RTP over UDP | 5060 |
The PolyAI RTP port range in both cases is **9000–49000**.
### Firewall
PolyAI uses static IP addresses for all of its SIP and RTP servers. If you need these to add to your firewall, please reach out to support.
### Certificates
* PolyAI supports **TLS version 1.2** for SIP over TLS.
* PolyAI uses the **DigiCert Global Root G2** certificate in all regions — [DigiCertGlobalRootG2.crt.pem](https://cacerts.digicert.com/DigiCertGlobalRootG2.crt.pem) (download).
* PolyAI supports client SIP servers with any publicly trusted Root Certificate in the [Mozilla 2026-07-16 CA Trust Bundle](https://curl.se/ca/cacert-2026-07-16.pem) (download).
## Identifying the SIP Trunk
If you're not connecting via the SIP Trunk's hostname, you must provide the SIP Trunk ID in **one** of:
* the `X-PolyAI-SIP-Trunk-ID` SIP header, or
* an `x-polyai-sip-trunk-id` request-URI parameter.
```text SIP header highlight={9} theme={"theme":{"light":"github-light","dark":"github-dark"}}
INVITE sip:1000@sbc.sip.eu.poly.ai SIP/2.0
Via: SIP/2.0/TLS 203.0.113.10:5061;branch=z9hG4bK74bf9
Max-Forwards: 70
From: "Example" ;tag=8675309
To:
Call-ID: 3c26700c8f2b4e1a9d5f@example.com
CSeq: 1 INVITE
Contact:
X-PolyAI-SIP-Trunk-ID: tr-0123456789abcdefghijklmn
Content-Type: application/sdp
Content-Length: 312
(SDP offer…)
```
```text Request-URI parameter highlight={1} theme={"theme":{"light":"github-light","dark":"github-dark"}}
INVITE sip:1000@sbc.sip.eu.poly.ai;x-polyai-sip-trunk-id=tr-0123456789abcdefghijklmn SIP/2.0
Via: SIP/2.0/TLS 203.0.113.10:5061;branch=z9hG4bK74bf9
Max-Forwards: 70
From: "Example" ;tag=8675309
To:
Call-ID: 3c26700c8f2b4e1a9d5f@example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: 312
(SDP offer…)
```
## Authenticating your calls
Authentication is optional per trunk. If you've configured it via the management API, your `INVITE` must satisfy it.
### Token-based auth
Send the token in the `X-PolyAI-SIP-Trunk-Token` header on your `INVITE`:
```text highlight={3} theme={"theme":{"light":"github-light","dark":"github-dark"}}
INVITE sip:1000@tr-0123456789abcdefghijklmn.sbc.sip.eu.poly.ai SIP/2.0
…
X-PolyAI-SIP-Trunk-Token: a-long-random-shared-secret
…
```
### Digest-based auth
Standard SIP digest authentication. PolyAI replies to your first `INVITE` with a `401 Unauthorized` carrying a `WWW-Authenticate` challenge built from the trunk's `realm`.
Your SIP server then re-sends the `INVITE` with an `Authorization` header computed from the trunk's `username` and `password`.
## Checklist for an inbound call
1. Connect over the right transport and port. If connecting over TLS, ensure you've uploaded PolyAI's Root Certificate and that your SIP server is using a supported TLS Certificate.
2. Select a hostname to connect to, providing the SIP Trunk ID if not using the SIP Trunk's unique hostname.
3. If the trunk has authentication, present the token header or answer the digest challenge.
4. Set the dialed user part to a configured **extension** so the call reaches the right agent, or configure a [default route](/api-reference/sip-trunking/endpoint/create-a-sip-trunk#default-route) for numbers without one.