--- title: Flow and API Configuration Guide for Voice AI & Contact Centre Platforms slug: dynamic-sip-trunking/flow-and-api-configuration-guide-for-voice-ai-and-contact-centre-platforms docTags: createdAt: 2025-09-29T14:37:57.951Z --- **** ## 1. Background & Objective Voice AI and Contact Center (CC) platforms often operate robust SIP-based (vSIP) infrastructures for AI-led and agent-assisted conversations. However, they typically lack direct access to India’s PSTN (landline and mobile networks) due to licensing and regulatory restrictions. **Exotel**, operating as a Unified License (UL) Virtual Network Operator (VNO), bridges this gap by offering compliant PSTN ingress/egress via its SIP Trunking solution. **Objective:** To provide a plug-and-play, regulatory-compliant PSTN connectivity layer for both Voice AI and CC platforms without disrupting their current SIP infrastructure, bot orchestration logic, or agent workflow. - Enable Voice AI and Contact Center platforms to access Indian PSTN via Exotel’s UL VNO. - Provide a plug-and-play SIP trunking layer without disrupting existing bot or agent logic. - Support both inbound and outbound PSTN call flows using Exotel’s vSIP infrastructure. - Streamline onboarding via APIs for trunk creation, DID mapping, and IP whitelisting. **This solution is ideal for:** - Voice AI platforms using SIP-based infrastructure (e.g., FreeSWITCH, Kamailio, Asterisk, custom SBCs) - Contact Center platforms with on-prem or cloud SIP setups requiring PSTN termination or origination - Companies seeking elastic and compliant PSTN connectivity without managing telco licensing - AI-led and hybrid inbound/outbound voice workflows ## 2. Solution Overview :::Heading{depth="3" indent="1"} **2.1 Architecture** ::: - **Partner Side**: Existing vSIP Endpoint / SBC / PBX (Voice AI or CC layer) - **Exotel Side**: UL VNO SIP Gateway connected to Indian PSTN via multiple telcos **Connectivity Options:** - Public Internet (default) - MPLS or VPN (optional for BFSI/secure deployments; contact CSM) **Media:** RTP/SRTP, supporting PCMA (G.711 A-law) and PCMU (G.711 μ-law) **Signaling:** SIP over TCP or TLS **Call Flow:** 1. **Outbound**: Partner SBC sends SIP INVITE (only from static IP) → Exotel SIP Gateway → Indian PSTN → Customer Phone 2. **Inbound**: PSTN Call → Exotel DID → SIP INVITE (from static IP or FQDN) to Partner SBC (for bot or agent) Exotel SIP Trunking – TCP Integration Guide Exotel SIP Trunking – TLS Integration Guide ### 2.2 Key Capabilities - Dynamic Channel Allocation for scale management - Multi-Telco Failover with 100% connectivity SLA - DID Management: Purchase & KYC compliant with Indian regulations - Secure Interconnects: IP whitelisting, TLS support - Regulatory Compliance: SDCA mapping, lawful interception readiness Exotel SIP Trunking – To-Flow Guide ## 3. Onboarding & Integration ### 3.1 Exotel Account Setup & KYC 1. **Create Account** – [Sign up on Exotel](https://my.in.exotel.com) and select **Browser Calling** during setup 2. **Complete KYC/CAF** – Upload KYC Documents ### 3.2 SIP Trunk Enablement 1. **Enable SIP Trunking** – Email hello\@exotel.com to activate trunking & provision a Virtual Number/Exophone 2. **Retrieve API Credentials** – Visit API Settings to get account\_sid, key, and token To configure silence ring or remove ring duration, contact your Exotel CSM or email hello\@exotel.com ### 3.3 Trunk Configuration via API Use: - [GitHub Repo](https://github.com/exotel/exotel-vsip-trunk-Configuration-API) - [Postman Collection](https://www.postman.com/grey-star-272776/exotel-vsip-trunk-configuration-apis/collection/u3vmluu/exotel-vsip-trunk-apis) API Steps: - `Create Trunk (/trunks)` - `Map DIDs (/trunks/{trunk_sid}/phone-numbers)` - `Whitelist IPs (/trunks/{trunk_sid}/whitelisted-ips)` - `Add Destination URIs ( TCP, TLS)` - Set trunk\_external\_alias for VN–FQDN mapping if required (for VAPI, LiveKit,OpenAI etc.) ## 4. Inbound Call Setup (PSTN → SIP Platform) - Create a Flow using **Connect Applet** in App Bazaar - Use `sip:` in the **Dial Whom** field ::Image[]{src="https://app.archbee.com/api/optimize/SK2urIgCC2ml99YyqWOSl/QK2UUNTg2BHO-HnMlym4I_screenshot-2025-09-29-at-82418-pm.png" size="84" width="2940" height="1382" position="center" darkWidth="2940" darkHeight="1382" showCaption="false"} - For custom routing, use a Dynamic URL to fetch destination URI and pass headers ::Image[]{src="https://s3.amazonaws.com/cdn.freshdesk.com/data/helpdesk/attachments/production/3051119684/original/_XHPYzAXt9eUmbaRl9wyMiWWYpl-Gxt5jQ.png?1581623042" size="46" width="448" height="302" position="center" darkWidth="448" darkHeight="302" showCaption="false"} - Supports **up to 3 custom SIP headers**, e.g., X-param1=value1 (max 200 bytes total) - Headers prefixed with Exotel- or Veeno- are platform-reserved **Connect Applet – Dynamic URL Response Example:** `{` `"fetch_after_attempt": false,` `"destination": { "trunk": "trunk-2134" },` `"custom_params": "param1=value1¶m2=value2",` `"record": true,` `"recording_channels": "dual"` `}` Reference: Connect Applet – Dynamic URL ## 5. Outbound Call Setup (Platform → PSTN) ### 5.1 Static IP Setup - Request IP whitelisting via Exotel Support or use above repo to get it done. - Once approved, initiate SIP outbound calls to Indian PSTN ### 5.2 FQDN-based Setup (API-triggered) - Configure trunk destination via API (only for FQDN-based use cases) - Use Click-to-Call API or Connect Customer to Flow API - Set destination as sip:\ in Connect Applet ## 6. Voicebot to Agent Handoff (SIP Flow) :::Heading{depth="3" indent="1"} **Flow:** ::: - Voicebot runs on Connect Applet over vSIP - Bot disconnects → Flow moves to Passthru Applet → calls webhook - Webhook Response: - 200 OK: Route to Connect Applet (agent group or SIP trunk) - 302/404: Move to Hangup Applet **Example:** `User says “Talk to human” → Bot ends → Passthru Applet → webhook (200 OK) → SwitchCase → Connect Applet (sip:)` ## 7. Benefits for Voice AI and CC Platforms - Plug-and-play PSTN access via Exotel’s UL VNO - Elastic scaling with dynamic channel allocation - Regulatory assurance with lawful interception readiness - TLS security for sensitive verticals - Real-time programmable call routing ## 8. Example Use Cases - AI-led outbound campaigns (sales/NPS) - Inbound IVR bots or reception assistants - Agent-bot hybrid support models - KYC calls and OTP verification for BFSI - Order confirmations and fraud checks for e-commerce ## 9. Next Steps - Share SIP endpoint details: IP/FQDN, transport type, supported codecs - Exotel team initiates CAF/KYC validation - Integration testing with live traffic - Commercial onboarding & production go-live