A practical, production-ready guide to configuring BSNL SIP PRI (IMS SIP Trunk) on modern Asterisk (PJSIP) with OpenVPN. Covers authentication, routing, user_eq_phone, scoring logic, debugging, and real-world carrier behavior. BSNL now delivers SIP PRI over FTTH fiber using IMS-based SIP signaling routed through VPN (OpenVPN or SoftEther). Key realities: SIP Proxy is reachable only via VPN SIP authentication may use: IMS expects proper user=phone format RTP may traverse different subnets If your PBX doesn’t support OpenVPN natively, you must deploy a router or gateway device that does. 🛠 Step 1 – Configure OpenVPN BSNL provides: VPN Server Primary IP VPN Server Secondary IP Virtual IP (Client) Gateway Mask After connecting: ip addr show tun0 ip route ping 10.x.x.x # SIP Proxy Ensure: VPN interface is UP Route to SIP proxy goes through VPN SIP proxy is reachable 🧩 Step 2 – Configure BSNL SIP Trunk (PJSIP – NOT chan_sip) Modern Asterisk uses PJSIP , not sip.conf. Below is a ...
The Hidden Asterisk + PJSIP + IMS Trap (BSNL Case Study) Why a perfectly registered SIP trunk can still make ZERO calls — and how to fix it Most SIP engineers panic when they see this: REGISTER → 401 → 200 OK Status: Registered …and then nothing happens . No outbound calls. No INVITE. No SIP logs. No errors. I recently debugged a BSNL IMS SIP trunk on Asterisk 20 (PJSIP) that worked flawlessly on another PBX — yet refused to place calls here. 👉 Credentials were correct 👉 Registration was successful 👉 Network & NAT were fine Still: no calls left the system This article explains why this happens , how to diagnose it , and how to fix it permanently . 🔍 The Illusion of “Trunk Working” In Asterisk, registration success does NOT mean call routing success . You can have: ✅ pjsip show registrations → Registered ❌ Zero outbound SIP traffic Because registration ≠ dialing . 🧠 The Real Root Cause (90% of Such Issues) Your dialplan never dials the trunk In modern PBX ar...