--- title: Connect Exotel SIP trunking to NLPearl.AI slug: exotel-agentstream/connect-exotel-sip-trunking-to-nlpearlai createdAt: 2026-04-01T17:43:03.773Z --- This guide connects **Exotel SIP trunking** to [NLPearl.AI ](https://platform.nlpearl.ai/)using NLPearl’s **Custom VoIP** feature, where **Exotel is the SIP carrier** behind NLPearl (NLPearl’s portal drives the AI agent; Exotel provides the PSTN DID and SIP trunk). **GitHub repo (reference):** https\://github.com/exotel/AgentStream-VoiceAIEcosystem :::BlockQuote **Applicability:** **UI-driven + API-driven** (Custom VoIP configuration in NLPearl portal; optional outbound via API). ::: :::BlockQuote **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. ::: ## NLPearl (from official docs) | Topic | Detail | | -------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Custom VoIP | [Custom VoIP integration](https://developers.nlpearl.ai/pages/custom_voip) — inbound SIP Domain shown after save; outbound requires SIP Trunk URL + User Part + optional auth | | Getting started | Getting started | | Outbound API | [Outbound](https://developers.nlpearl.ai/pages/outbound_api)/API and [Make Call API request](https://developers.nlpearl.ai/api-reference/v1/outbound/make-call) | | Variables / callData | [Variables](https://developers.nlpearl.ai/pages/variables) — callData used in Make Call / Lead APIs | ## Flows (what you configure) | Direction | What to configure | | -------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Outbound** (NLPearl → Exotel → PSTN) | **Exotel:** trunk + DID + **digest credentials**. **NLPearl:** Custom VoIP **Outbound** with **SIP Trunk URL** (Exotel trunk domain) + **User Part** + optional **credentials auth**. | | **Inbound** (PSTN → Exotel → NLPearl) | **NLPearl:** Custom VoIP **Inbound** (choose IP auth or credentials) → save to get a **SIP Domain**. **Exotel:** set trunk **destination-uris** to that NLPearl SIP Domain (plus transport/port). **Exotel Flow:** Connect using **sip:\**. | Important: **Outbound** does **not** need destination-uris. **Inbound** does. ## Part A — NLPearl portal (Custom VoIP) ### A1. Prepare the AI agent 1. Create and **publish** your agent (Pearl) in platform.nlpearl.ai. 2. Ensure the agent supports your required language/flow and is ready for inbound/outbound usage. ### A2. Add Custom VoIP phone number 1. Open **Settings** → **Phone Numbers**. 2. Click **Custom VoIP**. 3. Enter your **Exotel DID** in E.164 (display/reference). 4. Choose **Call direction**: inbound, outbound, or both. ### A3. Configure Outbound (Exotel as SIP trunk) In the **Outbound configuration** section ([Custom VoIP docs](https://developers.nlpearl.ai/pages/custom_voip)): - **TLS (SRTP) Encryption**: enable only if you will use **SIP TLS** to Exotel and Exotel confirms TLS/SRTP requirements for your account. - **SIP Trunk URL**: set to Exotel trunk SIP domain: - sip:${ACCOUNT\_SID}.pstn.exotel.com (recommended form), or - ${ACCOUNT\_SID}.pstn.exotel.com if NLPearl UI expects host-only. - **User Part**: use one of: - your Exotel trunk **digest username**, or - your DID in E.164 (if you want the SIP From-user to mirror the DID). - **Authentication methods (Credentials Authentication)**: if enabled, set the **same** username/password as Exotel **POST .../credentials**. - **Data center**: pick the closest region to Exotel’s SIP edge for latency. ### A4. Configure Inbound (NLPearl receives from Exotel) In the **Inbound configuration** section (Custom VoIP docs): - **TLS (SRTP) Encryption**: enable only if you will use TLS/SRTP and Exotel confirms. - **Authentication**: - **Credentials Authentication**: recommended when you don’t have stable IPs and want strict auth. - **IP Address Authentication**: only if Exotel provides the fixed IPs NLPearl should accept traffic from. After saving inbound settings, NLPearl shows a **SIP Domain to connect**. You will copy that domain into Exotel **destination-uris** (Part B). ## Part B — Exotel APIs **Auth:** API\_KEY\:API\_TOKEN\@api.in.exotel.com · **200 requests/minute (SIP trunk APIs)** · \_exotel-trunk-api-snippets.md ### B1. Create trunk + map DID + set digest credentials (outbound prerequisite) Use the shared snippets: - Create trunk - Map phone number (DID) - POST .../credentials For NLPearl **Outbound**, these digest credentials should match what you configure in NLPearl’s **Outbound** auth section. [Exotel SIP trunk API Reference for Voice AI](docId\:jQ98JRRnXtZaUDYoGOdMZ) ### B2. Inbound routing: set destination URI toward NLPearl SIP Domain Once NLPearl gives you a **SIP Domain**, set it as the trunk destination URI: :::BlockQuote curl -s -X PUT "https\://${API\_KEY}:${API\_TOKEN}@${SUBDOMAIN}/v2/accounts/${ACCOUNT\_SID}/trunks/${TRUNK\_SID}/destination-uris" \\ -H "Content-Type: application/json" \\ -d '\{ "destinations": \[ \{ "destination": "YOUR\_NLPEARL\_SIP\_DOMAIN:5061;transport=tls" } ] }' ::: Notes: - Use **the exact domain** NLPearl shows after saving inbound config. - Align **port + transport** with how you configured NLPearl (TLS vs TCP). If you’re unsure, start with what Exotel supports for your SIP trunking and what NLPearl’s Custom VoIP expects. ### B3. Exotel Flow: Connect applet In your Exotel flow, use: - **Applet**: Connect - **Dial whom**: sip:\ (trunk\_sid is the value returned by create trunk; it is not a SIP URI.) ## Tests (quick) ### Outbound (NLPearl → PSTN) 1. In NLPearl, create/assign an outbound activity using the Custom VoIP number. 2. Trigger a test call from the UI and confirm Exotel sees SIP invites on the trunk. 3. If using API-driven outbound, use the Make Call endpoint per docs: [Make Call API request.](https://developers.nlpearl.ai/api-reference/v1/outbound/make-call) ### Inbound (PSTN → NLPearl) 1. Call the Exotel DID from a mobile phone. 2. Verify Exotel routes to trunk (Flow Connect sip:\) and then to the trunk destination-uris (NLPearl SIP Domain). 3. Confirm NLPearl receives the call and the assigned agent answers. ## Troubleshooting | Symptom | Likely cause | Fix | | ------------------------------------------------ | ------------------------------ | ----------------------------------------------------------------------------------------------------------------------- | | 401/403 on outbound SIP | Digest mismatch | Ensure NLPearl outbound credentials match Exotel POST .../credentials exactly | | Inbound reaches Exotel but not NLPearl | Missing/wrong destination-uris | Paste NLPearl SIP Domain exactly; confirm port/transport; re-GET destination URIs | | TLS failures | TLS/SRTP toggles mismatched | Keep TLS/SRTP off on both sides for first smoke test unless Exotel confirms required TLS/SRTP; then enable consistently | | Confusing auth failures after enabling allowlist | ACL + digest interaction | Remove whitelisted-ips unless you have dedicated /32 static IP requirements; rely on digest and coordinate with Exotel |