Day 8 - Why Did This Teams Call Fail? Real SIP Ladder Analysis

A Teams user calls. It rings twice. Drops. The SBC shows registered. The carrier says healthy. Teams Admin Center shows no errors. Everything looks fine — and yet every call is failing. The answer was in the SIP ladder. It always is. In this video we walk through a real Teams Direct Routing call failure from first ring to root cause — reading the SIP trace the way a senior UC engineer reads it, finding exactly where the call died, and fixing it in 22 minutes. What's covered: ✅ How to read a SIP ladder — actors, arrows, time axis, and the 3 things you look for in every failed call ✅ Normal vs failed call ladder — where this one diverges from a successful call ✅ Live trace analysis — 404 Not Found from the carrier, expanding the INVITE headers ✅ Root cause — a legacy number translation rule stripping +44 from every outbound number, surviving a carrier migration nobody cleaned up ✅ The fix + verification trace — 200 OK confirmed ✅ The 5-step SIP ladder methodology — apply this to any failed Teams DR call ⚠️ The key lesson: The SBC was working perfectly. The carrier trunk was up. The dial plan was wrong — and without opening the SIP trace, you would never find it. 📋 SIP Response Code Quick Reference: 404 — Number not found at carrier (number format) 488 — Not acceptable here (codec mismatch) ← Day 9 403 — Forbidden (routing policy / licensing) 503 — Service unavailable (trunk down) 📌 Day 8 of the 50-Day UC & Collaboration Sprint. Week 2: Voice Disasters — real incidents, real traces, real fixes. Subscribe so you don't miss Day 9: SIP 488 Not Acceptable Here. ───────────────────────────────────── 🔔 SUBSCRIBE for daily UC & Collaboration content ───────────────────────────────────── Join this channel to get access to perks:    / @technicalventure   SIP Video -    • Lecture-1 | SIP | Part-1 | Session Initiat...   CUCM Playlist -    • Cisco Unified Communications Manager (CUCM...   CUC Playlist -    • Cisco Unity Connection(CUC)   WebEx Playlist -    • Cisco WebEx Control Hub