Connect Exotel SIP trunking to Retell AI

8 min

This guide connects Exotel SIP trunking to Retell AI using elastic SIP per Retell custom telephony, with Exotel as the Indian PSTN provider.

GitHub repo (reference): https://github.com/exotel/AgentStream-VoiceAIEcosystem

Applicability: UI-driven (Retell dashboard custom telephony) with optional API-driven call control.

Edge hostnames you may see (India): in.voip.exotel.com:5070 (TCP) and in.voip.exotel.com:443 (TLS). Use the exact host/IP + port + transport Exotel assigns. See _exotel-trunk-api-snippets.md.

ACL vs digest (important): Exotel trunk ACL is intended for static /32 IPs only (mask: 32), not CIDR ranges. If Retell provides CIDR ranges (common), do not attempt to whitelist ranges on Exotel—prefer digest and coordinate with Exotel/provider support if you see auth/routing issues.

Full reference: retell/integrations/exotel-vsip/retell-exotel-voice-ai-connector.md

Quickstart: retell/integrations/exotel-vsip/QUICKSTART.md

Retell (from official docs)

SIP server: sip:sip.retellai.com with ;transport=tcp (or tls / udp) — Custom telephony.

Retell publishes IP ranges for carriers to allowlist toward Retell; on Exotel trunk ACL, you can only add static single IPs (mask: 32) per Exotel — not full CIDR ranges on the trunk. If Retell gives ranges, coordinate with Exotel or use digest auth.

Flows

Direction	What to configure
Outbound SIP	Exotel: create trunk → map DID → credentials. Optional whitelisted-ips only if Retell provides a fixed static egress IP (one IP per POST, mask: 32).
Inbound SIP	Exotel: destination URI on trunk toward Retell (sip.retellai.com host/port/transport per Retell). Connect applet: sip:<trunk_sid> in Dial whom (value = API trunk_sid, not a full URI).

Part A — Retell

Configure agent; import Exotel DID after Exotel trunk exists (Custom telephony).

Match digest to Exotel POST .../credentials for outbound termination.

Part B — Exotel APIs

Auth: API_KEY:[email protected] · 200 requests/minute (SIP trunk APIs) ·

Exotel SIP trunk API Reference for Voice AIAPIs

Outbound SIP

Create trunk

Map DID

POST .../credentials

(Optional) whitelisted-ips — only for a static IP from Retell, mask: 32

Inbound SIP

POST .../destination-uris — example shape (confirm port/transport with Retell):

curl -s -X POST "https://${API_KEY}:${API_TOKEN}@${SUBDOMAIN}/v2/accounts/${ACCOUNT_SID}/trunks/${TRUNK_SID}/destination-uris" \ -H "Content-Type: application/json" \ -d '{ "destinations": [ { "destination": "sip.retellai.com:5060;transport=tcp" } ] }'

Connect: sip:<trunk_sid> in Dial whom.

Dial to SIP URI (alternative)

References

Resource	URL
Retell dashboard	https://dashboard.retellai.com/
Retell — custom telephony	https://docs.retellai.com/deploy/custom-telephony
Retell — quick start	https://docs.retellai.com/get-started/quick-start
Exotel SIP API	https://docs.exotel.com/dynamic-sip-trunking/detailed-sip-trunking-api-reference