{"slug":"conference-bridging","title":"Conference Bridging — SIP Mixers, Mute, Recording, Coaching","tags":["conference","bridge","mixer","signalwire","swml","multi-party"],"agent_summary":"Conference bridging mixes 3+ audio streams into a single shared room. SignalWire conferences are named rooms; participants join by routing a call into `connect: { to: conference:name }`. Supports mute/unmute, hold, beep on entry/exit, recording, talk-detection, coaching (whisper), barge-in, and dial-out to add participants mid-call.","trigger_phrases":["SignalWire conference","conference bridge","multi party call","join conference room","conference mute","conference coaching","barge in conference"],"runnable":true,"markdown":"\n# Conference Bridging\n\nA conference room is a named audio mixer. Multiple participants join, all audio mixes together, all participants hear the mix. SignalWire conferences are the building block for warm transfers, team huddles, customer-agent-supervisor coaching sessions, and ad-hoc group calls.\n\n## Conference vs connect — when to use which\n\n| Need | Use |\n|---|---|\n| Two-party call | `connect` (peer-to-peer through SignalWire) |\n| Three or more parties | `conference` |\n| Need mute/coach controls | `conference` |\n| Need recording with separate tracks | `conference` (stereo or per-leg) |\n| Just bridging two PSTN endpoints | `connect` (lower cost, simpler) |\n\n## Basic join\n\nSWML:\n\n```yaml\nversion: 1.0.0\nsections:\n main:\n - answer: {}\n - connect:\n to: conference:weekly_standup\n```\n\nLaML:\n\n```xml\n\n \n weekly_standup\n \n\n```\n\nAny caller hitting this script joins the room named `weekly_standup`. First participant typically hears music-on-hold until a second participant joins; configurable.\n\n## Conference verb parameters (LaML/SWML)\n\n| Parameter | Default | Notes |\n|---|---|---|\n| `beep` | `true` | Play a beep when participant enters/leaves |\n| `muted` | `false` | Join muted (can be unmuted via API) |\n| `start_conference_on_enter` | `false` | When true, the conference starts only when this participant joins (admin pattern) |\n| `end_conference_on_exit` | `false` | When true, all participants leave when this participant leaves (host pattern) |\n| `wait_url` | (silence or default music) | URL or TTS to play while alone |\n| `max_participants` | 250 | Hard cap |\n| `record` | `false` | Record the entire conference |\n| `recording_status_callback` | none | Webhook fires when recording completes |\n| `region` | (closest) | Force a specific region for the mixer |\n| `coach` | none | Participant SID to coach (whisper-only) |\n| `region` | nearest | Force a media region for latency optimization |\n\n## Host and participant roles\n\nThe host pattern uses `start_conference_on_enter` and `end_conference_on_exit`:\n\n```xml\n\n\n \n \n meeting_42\n \n \n\n\n\n\n \n \n meeting_42\n \n \n\n```\n\nParticipants wait on hold until the host joins. When the host leaves, everyone is disconnected.\n\n## Naming conventions\n\nConference rooms are global — any participant joining `weekly_standup` joins the same room. Two key implications:\n\n1. **Names must be unique per use case** — using `support` as a conference name will collide across customers.\n2. **Use deterministic, prefixed names** — `cust_${customer_id}_${session_id}` avoids collisions.\n\nFor ephemeral conferences (warm transfer rooms, ad-hoc bridges):\n\n```yaml\n- connect:\n to: conference:transfer_${call.id}\n```\n\nThe `${call.id}` is unique to the originating call, so each transfer gets its own room.\n\n## Adding participants mid-call\n\nTo bring in an additional party while a conference is in progress, place an outbound call to the new party with SWML/TwiML that joins them to the same conference name:\n\n```python\nclient.calls.create(\n to=\"+13105553333\",\n from_=\"+12125551111\",\n url=\"https://your.api/conference-join.xml?room=cust_42_abc\"\n)\n```\n\n```xml\n\n \n cust_42_abc\n \n\n```\n\n## Mute and unmute\n\nVia the LaML/REST API on the participant resource:\n\n```bash\ncurl -X POST \"https://{space}/api/laml/2010-04-01/Accounts/{project}/Conferences/{conf_sid}/Participants/{call_sid}.json\" \\\n -u \"${PROJECT}:${TOKEN}\" \\\n -d \"Muted=true\"\n```\n\nSet `Muted=false` to unmute. Useful for an admin/host UI that displays the conference roster with mute toggles.\n\n## Hold\n\nPlace a single participant on hold (they hear hold music, others continue talking):\n\n```bash\ncurl -X POST \".../Participants/{call_sid}.json\" \\\n -d \"Hold=true\" \\\n -d \"HoldUrl=http://twimlets.com/holdmusic\"\n```\n\n## Recording\n\nSet `record=\"record-from-start\"` on the conference:\n\n```xml\n\n meeting_42\n\n```\n\nModes:\n\n| Mode | Behavior |\n|---|---|\n| `do-not-record` | No recording (default) |\n| `record-from-start` | Start when the first participant joins |\n| `record-from-answer` | Same as `record-from-start` for conferences |\n\nRecording is a single mixed file. For separate per-participant tracks, record each individual leg via `Dial`'s `record` attribute and reconcile in post.\n\n## Coaching (whisper)\n\nCoaching is when a supervisor joins a conference but only one specific participant (the agent) hears them — the customer doesn't. Useful for live training and quality assurance.\n\n```python\nclient.calls.create(\n to=\"sip:supervisor@example.com\",\n from_=\"+12125551111\",\n url=f\"https://your.api/coach.xml?coach={agent_call_sid}&room=cust_42_abc\"\n)\n```\n\n```xml\n\n \n cust_42_abc\n \n\n```\n\n`coach` attribute set to the agent's CallSid → supervisor's audio goes only to the agent.\n\n## Barge-in\n\nBarge-in is when a supervisor joins as a full participant (everyone hears them). No special parameter — just join the conference normally.\n\nA common workflow is \"monitor → whisper → barge\":\n\n1. Supervisor joins muted (monitor only).\n2. Supervisor unmutes to whisper (coach attribute on agent only).\n3. Supervisor removes coach attribute → full barge-in.\n\n## Talk detection events\n\nConferences can fire a webhook when participants start or stop talking:\n\n```xml\n\n meeting_42\n\n```\n\nEvents delivered:\n\n| Event | Trigger |\n|---|---|\n| `join` | Participant joined |\n| `leave` | Participant left |\n| `mute` | Participant muted/unmuted |\n| `hold` | Participant placed on/off hold |\n| `talking` | Talk-detection threshold crossed |\n| `start` | Conference started (first participant) |\n| `end` | Conference ended (last participant left) |\n\nUseful for showing live conference UI (\"Bob is talking now\") or detecting silent participants.\n\n## Wait URL — music while alone\n\nDefault wait behavior plays SignalWire's hold music. Override for branded experience:\n\n```xml\n\n meeting_42\n\n```\n\nOr for dynamic wait audio (different music, announcements, \"estimated wait time\"):\n\n```xml\n\n meeting_42\n\n```\n\nYour endpoint returns TwiML with `` or `` instructions that loop.\n\n## Max participants and pricing\n\n| Plan tier | Max participants | Pricing model |\n|---|---|---|\n| Standard | 250 | Per-participant per-minute |\n| Enterprise | Higher (negotiated) | Per-minute + flat conference fee |\n\nPer-participant per-minute billing means a 30-minute conference with 5 participants = 150 billable minutes.\n\n## Region selection\n\nConferences are mixed in a SignalWire region. By default, the region is chosen based on the first participant. To force a region for latency optimization:\n\n```xml\nmeeting_42\n```\n\nRegions: `us1` (US East), `us2` (US West), `eu1` (Europe), `eu2`, `au1` (Australia). Pick the region geographically closest to most participants.\n\n## REST conference resource\n\nList active conferences:\n\n```bash\nGET /api/laml/2010-04-01/Accounts/{project}/Conferences.json?Status=in-progress\n```\n\nUpdate conference attributes mid-flight (e.g., end the conference, mute all):\n\n```bash\nPOST /api/laml/2010-04-01/Accounts/{project}/Conferences/{conf_sid}.json\n Status=completed\n```\n\nThis terminates the conference and disconnects all participants.\n\n## Common patterns\n\n### Three-way call\n\nA is on a call with B. A wants to add C. The standard pattern:\n\n1. Move A's leg into a conference: redirect A's call to SWML that joins conference `triple_${call_id}`.\n2. Move B's leg into the same conference: redirect B's call to SWML joining the same conference.\n3. Dial out to C, route to SWML joining the same conference.\n\nA, B, C are all conferenced.\n\n### Customer-agent-supervisor coaching\n\n1. Customer-agent call active (peer-to-peer).\n2. Supervisor wants to listen → redirect the agent leg into a conference, dial out and redirect the customer leg into the same conference.\n3. Supervisor joins the conference with `coach=${agent_call_sid}` — only the agent hears them.\n\n### Town hall\n\nHost + 100 listeners. Host joins normally. Listeners join with `muted=\"true\"` and `endConferenceOnExit=\"false\"`. Host's `endConferenceOnExit=\"true\"` ends the meeting when the host leaves.\n\n## Common pitfalls\n\n- **Beep fatigue** — default beep on every join/leave is annoying with large groups. Set `beep=\"false\"`.\n- **Host disconnect ends call for all** — if host's network drops momentarily and `endConferenceOnExit=\"true\"`, the entire conference dies. Consider grace periods or co-hosts.\n- **Recording without consent** — see [call recording compliance](/topic/call-recording-compliance). Conferences with consent-required participants need affirmative consent.\n- **Conference name collision** — using `meeting` as a name globally collides. Always namespace.\n- **Forgetting `startConferenceOnEnter`** — without it, first participant hears music indefinitely.\n\n## Related patterns\n\n- [Warm transfer](/topic/warm-transfer) — typically implemented via conference\n- [Cold transfer](/topic/cold-transfer)\n- [Call recording compliance](/topic/call-recording-compliance) — multi-party recording rules\n- [Call routing strategies](/topic/call-routing-strategies)\n\n## References\n\n- SignalWire LaML `` documentation\n- SignalWire SWML `connect: conference:` syntax\n- RFC 4575 — SIP Event Package for Conference State\n","html":"

Conference Bridging

\n

A conference room is a named audio mixer. Multiple participants join, all audio mixes together, all participants hear the mix. SignalWire conferences are the building block for warm transfers, team huddles, customer-agent-supervisor coaching sessions, and ad-hoc group calls.

\n

Conference vs connect — when to use which

\n

| Need | Use |\n|---|---|\n| Two-party call | connect (peer-to-peer through SignalWire) |\n| Three or more parties | conference |\n| Need mute/coach controls | conference |\n| Need recording with separate tracks | conference (stereo or per-leg) |\n| Just bridging two PSTN endpoints | connect (lower cost, simpler) |

\n

Basic join

\n

SWML:

\n
version: 1.0.0\nsections:\n  main:\n    - answer: {}\n    - connect:\n        to: conference:weekly_standup\n
\n

LaML:

\n
<Response>\n  <Dial>\n    <Conference>weekly_standup</Conference>\n  </Dial>\n</Response>\n
\n

Any caller hitting this script joins the room named weekly_standup. First participant typically hears music-on-hold until a second participant joins; configurable.

\n

Conference verb parameters (LaML/SWML)

\n

| Parameter | Default | Notes |\n|---|---|---|\n| beep | true | Play a beep when participant enters/leaves |\n| muted | false | Join muted (can be unmuted via API) |\n| start_conference_on_enter | false | When true, the conference starts only when this participant joins (admin pattern) |\n| end_conference_on_exit | false | When true, all participants leave when this participant leaves (host pattern) |\n| wait_url | (silence or default music) | URL or TTS to play while alone |\n| max_participants | 250 | Hard cap |\n| record | false | Record the entire conference |\n| recording_status_callback | none | Webhook fires when recording completes |\n| region | (closest) | Force a specific region for the mixer |\n| coach | none | Participant SID to coach (whisper-only) |\n| region | nearest | Force a media region for latency optimization |

\n

Host and participant roles

\n

The host pattern uses start_conference_on_enter and end_conference_on_exit:

\n
<!-- Host -->\n<Response>\n  <Dial>\n    <Conference startConferenceOnEnter=\"true\" endConferenceOnExit=\"true\">\n      meeting_42\n    </Conference>\n  </Dial>\n</Response>\n\n<!-- Participant -->\n<Response>\n  <Dial>\n    <Conference startConferenceOnEnter=\"false\" endConferenceOnExit=\"false\">\n      meeting_42\n    </Conference>\n  </Dial>\n</Response>\n
\n

Participants wait on hold until the host joins. When the host leaves, everyone is disconnected.

\n

Naming conventions

\n

Conference rooms are global — any participant joining weekly_standup joins the same room. Two key implications:

\n
    \n
  1. Names must be unique per use case — using support as a conference name will collide across customers.
    2. \n
  2. Use deterministic, prefixed names — cust_${customer_id}_${session_id} avoids collisions.
    3. \n
\n

For ephemeral conferences (warm transfer rooms, ad-hoc bridges):

\n
- connect:\n    to: conference:transfer_${call.id}\n
\n

The ${call.id} is unique to the originating call, so each transfer gets its own room.

\n

Adding participants mid-call

\n

To bring in an additional party while a conference is in progress, place an outbound call to the new party with SWML/TwiML that joins them to the same conference name:

\n
client.calls.create(\n    to=\"+13105553333\",\n    from_=\"+12125551111\",\n    url=\"https://your.api/conference-join.xml?room=cust_42_abc\"\n)\n
\n
<Response>\n  <Dial>\n    <Conference>cust_42_abc</Conference>\n  </Dial>\n</Response>\n
\n

Mute and unmute

\n

Via the LaML/REST API on the participant resource:

\n
curl -X POST \"https://{space}/api/laml/2010-04-01/Accounts/{project}/Conferences/{conf_sid}/Participants/{call_sid}.json\" \\\n  -u \"${PROJECT}:${TOKEN}\" \\\n  -d \"Muted=true\"\n
\n

Set Muted=false to unmute. Useful for an admin/host UI that displays the conference roster with mute toggles.

\n

Hold

\n

Place a single participant on hold (they hear hold music, others continue talking):

\n
curl -X POST \".../Participants/{call_sid}.json\" \\\n  -d \"Hold=true\" \\\n  -d \"HoldUrl=http://twimlets.com/holdmusic\"\n
\n

Recording

\n

Set record=\"record-from-start\" on the conference:

\n
<Conference record=\"record-from-start\"\n            recordingStatusCallback=\"https://your.api/conf-recording\">\n  meeting_42\n</Conference>\n
\n

Modes:

\n

| Mode | Behavior |\n|---|---|\n| do-not-record | No recording (default) |\n| record-from-start | Start when the first participant joins |\n| record-from-answer | Same as record-from-start for conferences |

\n

Recording is a single mixed file. For separate per-participant tracks, record each individual leg via Dial's record attribute and reconcile in post.

\n

Coaching (whisper)

\n

Coaching is when a supervisor joins a conference but only one specific participant (the agent) hears them — the customer doesn't. Useful for live training and quality assurance.

\n
client.calls.create(\n    to=\"sip:supervisor@example.com\",\n    from_=\"+12125551111\",\n    url=f\"https://your.api/coach.xml?coach={agent_call_sid}&room=cust_42_abc\"\n)\n
\n
<Response>\n  <Dial>\n    <Conference coach=\"{agent_call_sid}\">cust_42_abc</Conference>\n  </Dial>\n</Response>\n
\n

coach attribute set to the agent's CallSid → supervisor's audio goes only to the agent.

\n

Barge-in

\n

Barge-in is when a supervisor joins as a full participant (everyone hears them). No special parameter — just join the conference normally.

\n

A common workflow is \"monitor → whisper → barge\":

\n
    \n
  1. Supervisor joins muted (monitor only).
    2. \n
  2. Supervisor unmutes to whisper (coach attribute on agent only).
    3. \n
  3. Supervisor removes coach attribute → full barge-in.
    4. \n
\n

Talk detection events

\n

Conferences can fire a webhook when participants start or stop talking:

\n
<Conference statusCallback=\"https://your.api/conf-events\"\n            statusCallbackEvent=\"join leave mute hold talking\">\n  meeting_42\n</Conference>\n
\n

Events delivered:

\n

| Event | Trigger |\n|---|---|\n| join | Participant joined |\n| leave | Participant left |\n| mute | Participant muted/unmuted |\n| hold | Participant placed on/off hold |\n| talking | Talk-detection threshold crossed |\n| start | Conference started (first participant) |\n| end | Conference ended (last participant left) |

\n

Useful for showing live conference UI (\"Bob is talking now\") or detecting silent participants.

\n

Wait URL — music while alone

\n

Default wait behavior plays SignalWire's hold music. Override for branded experience:

\n
<Conference waitUrl=\"https://cdn.example.com/hold-music.mp3\"\n            waitMethod=\"GET\">\n  meeting_42\n</Conference>\n
\n

Or for dynamic wait audio (different music, announcements, \"estimated wait time\"):

\n
<Conference waitUrl=\"https://your.api/wait-twiml\">\n  meeting_42\n</Conference>\n
\n

Your endpoint returns TwiML with <Play> or <Say> instructions that loop.

\n

Max participants and pricing

\n

| Plan tier | Max participants | Pricing model |\n|---|---|---|\n| Standard | 250 | Per-participant per-minute |\n| Enterprise | Higher (negotiated) | Per-minute + flat conference fee |

\n

Per-participant per-minute billing means a 30-minute conference with 5 participants = 150 billable minutes.

\n

Region selection

\n

Conferences are mixed in a SignalWire region. By default, the region is chosen based on the first participant. To force a region for latency optimization:

\n
<Conference region=\"us2\">meeting_42</Conference>\n
\n

Regions: us1 (US East), us2 (US West), eu1 (Europe), eu2, au1 (Australia). Pick the region geographically closest to most participants.

\n

REST conference resource

\n

List active conferences:

\n
GET /api/laml/2010-04-01/Accounts/{project}/Conferences.json?Status=in-progress\n
\n

Update conference attributes mid-flight (e.g., end the conference, mute all):

\n
POST /api/laml/2010-04-01/Accounts/{project}/Conferences/{conf_sid}.json\n  Status=completed\n
\n

This terminates the conference and disconnects all participants.

\n

Common patterns

\n

Three-way call

\n

A is on a call with B. A wants to add C. The standard pattern:

\n
    \n
  1. Move A's leg into a conference: redirect A's call to SWML that joins conference triple_${call_id}.
    2. \n
  2. Move B's leg into the same conference: redirect B's call to SWML joining the same conference.
    3. \n
  3. Dial out to C, route to SWML joining the same conference.
    4. \n
\n

A, B, C are all conferenced.

\n

Customer-agent-supervisor coaching

\n
    \n
  1. Customer-agent call active (peer-to-peer).
    2. \n
  2. Supervisor wants to listen → redirect the agent leg into a conference, dial out and redirect the customer leg into the same conference.
    3. \n
  3. Supervisor joins the conference with coach=${agent_call_sid} — only the agent hears them.
    4. \n
\n

Town hall

\n

Host + 100 listeners. Host joins normally. Listeners join with muted=\"true\" and endConferenceOnExit=\"false\". Host's endConferenceOnExit=\"true\" ends the meeting when the host leaves.

\n

Common pitfalls

\n
    \n
  • Beep fatigue — default beep on every join/leave is annoying with large groups. Set beep=\"false\".
    • \n
  • Host disconnect ends call for all — if host's network drops momentarily and endConferenceOnExit=\"true\", the entire conference dies. Consider grace periods or co-hosts.
    • \n
  • Recording without consent — see call recording compliance. Conferences with consent-required participants need affirmative consent.
    • \n
  • Conference name collision — using meeting as a name globally collides. Always namespace.
    • \n
  • Forgetting startConferenceOnEnter — without it, first participant hears music indefinitely.
    • \n
\n

Related patterns

\n\n

References

\n
    \n
  • SignalWire LaML <Conference> documentation
    • \n
  • SignalWire SWML connect: conference: syntax
    • \n
  • RFC 4575 — SIP Event Package for Conference State
    • \n
\n"}