What it is, mechanically
Audio Conferencing gives the ORGANIZER'S meetings a PSTN door: service numbers (shared, high-capacity) with per-meeting conference IDs. The licence sits on the organizer — attendees just dial. The invite's numbers come from the organizer's assigned bridge; extra toll/toll-free numbers can be acquired and assigned per organizer community.
Included in E5; add-on otherwise; a no-additional-cost variant covers dial-in for many SKUs — but dial-out is where money moves:
- Dial-out ("call me at…") and organizer-initiated add-a-phone-number consume from a shared Communications Credits / dial-out minute pool with per-country zones. One enthusiastic international project team can drain it; then dial-out fails org-wide and it looks like an outage.
- Toll-free numbers bill per minute of inbound use.
The switches that matter
| Switch | Effect |
|---|---|
Get-CsOnlineDialInConferencingTenantSettings |
Entry/exit announcements, PIN length, notifications |
| Per-user conferencing settings | Their bridge number, PIN resets, allow dial-out toggle |
Get-CsOnlineDialOutPolicy (13 instances in a typical tenant — ours scans them) |
WHO may dial out, domestic vs international — your cost-control lever |
| Entry/exit announcements | Compliance nicety; also the classic "who just joined" noise complaint |
Failure signatures
| Symptom | Cause |
|---|---|
| Invite has no dial-in numbers | Organizer unlicensed for Audio Conferencing — not a bug |
| "Conference ID not valid" | Stale invite reused after organizer licence/bridge change; regenerate |
| Dial-out fails for everyone | Credits pool empty — check Communications Credits balance |
| Dial-out fails for one user | Their OnlineDialOutPolicy restricts destination zone |
| PSTN caller stuck in lobby forever | Lobby settings treat dial-in as anonymous; nobody watching the lobby |
What to watch (proofs)
- Licence-to-bridge proof:
Get-CsOnlineDialInConferencingUser(or per-user bridge info) — organizer's number assignment; absence explains the empty invite. - Cost telemetry: TAC PSTN usage reports (dial-out minutes by user/destination) and the Communications Credits balance — the "outage" that is actually £0 remaining.
- Policy truth:
Get-CsOnlineDialOutPolicyinstances (scanned nightly) — your dial-out stance per user class; drift here is a cost event, and serv365 flags it. - Bridge behaviour:
Get-CsOnlineDialInConferencingTenantSettings(in the scan) — announcements/PIN config, the compliance-relevant bits, versioned over time.