---
title: Multicasts
summary: 'A multicast is a paging group: one announcement that goes out simultaneously to many SIP devices.'
section: features
tags:
  - crud
  - telephony
  - paging
updated: '2026-06-17'
---

> A **multicast** is a paging group: one announcement that goes out simultaneously to many SIP devices. Pick the recipients, pick the audio, trigger the multicast - every targeted phone plays the message at the same time.

## Overview

A multicast is the office PA system for IP phones: overhead pages, emergency announcements, lunch calls. The PBX ships with a fixed number of multicast slots, pre-allocated rather than user-creatable, so you configure existing slots rather than add new ones. Raise a support request if you need more. You do not trigger a multicast from this page - it fires from a *Multicast* call flow step, a phone keypress, or the API.

## What it does

Multicast paging is **one-way** audio, from the PBX to the targets. When an inbound caller triggers a multicast via a call flow step, the caller's audio is what gets broadcast to the targets.

**Place call** selects the delivery mode and is the most consequential setting:

- **Off (streaming)** - the platform sends a single network stream that subscribed phones play at once. Most efficient regardless of phone count, but multicast traffic must be routable on your network and phones must support it. Streaming requires a sound file, so this mode cannot be selected without one.
- **On (call-based)** - the platform places an individual SIP call to each device. Works across segments that block multicast and on any SIP phone, but one call per device adds load (200 devices means 200 simultaneous calls).

Use streaming by default. Switch to call-based only when your network or phones cannot do multicast.

**Priority** flags the page to interrupt non-priority audio already playing on the target devices. Reserve priority for emergency announcements so routine pages do not cut across each other.

**Targets** are a **union** of seven pickers (Users, SIP devices, Groups, Tags, Pools, Locations, Languages) - each picker adds to the same recipient set, so adding a user to a targeted group adds them to the page automatically. An optional **PIN** guards triggering from a keypad or external system.

## See also

- [Call flow steps](call_flow_steps.md) - the *Multicast* step that triggers a multicast from inbound calls.
- [Announcements](announcements.md) - the sound files multicasts play.
- [Groups](groups.md), [Tags](tags.md), [Pools](pools.md) - the dynamic target sources.
- [SIP devices](sip_devices.md) - the phones that receive multicast audio.

```yaml fields
group_number:
  label: 'Group number'
  tab: General
  hint: 'The unique numeric identifier for this multicast group. Assigned by the system and cannot be changed.'
name:
  label: Name
  tab: General
  hint: 'A descriptive name for this multicast group (for example "Building A Paging" or "Emergency Broadcast").'
ip_port:
  label: 'IP address and port number'
  tab: General
  hint: 'The multicast IP address and port number used for audio streaming. Configured by the system and cannot be changed.'
priority:
  label: Priority
  tab: General
  hint: 'When turned on, this multicast interrupts non-priority audio on the target devices. Does not interrupt active phone calls.'
place_call:
  label: 'Place call'
  tab: General
  hint: 'When turned on, the multicast places an individual call to each target device. When off, audio is streamed via multicast. Cannot be turned off if no announcement sound file is configured.'
comment:
  label: Comment
  tab: General
  hint: 'An optional internal note about this multicast group. You can edit this directly from the list view.'
soundFile:
  label: 'Sound file'
  tab: General
  hint: 'The announcement sound file played when the multicast is triggered. Only sound files of type Announcement can be selected.'
users:
  label: Users
  tab: General
  hint: 'Users whose SIP devices will receive the multicast audio.'
groups:
  label: Groups
  tab: General
  hint: "Groups whose members' devices will receive the multicast audio."
tags:
  label: Tags
  tab: General
  hint: 'Users with these tags will receive the multicast audio on their devices.'
pools:
  label: Pools
  tab: General
  hint: 'Pools whose members will receive the multicast audio.'
locations:
  label: Locations
  tab: General
  hint: 'Devices at these locations will receive the multicast audio.'
languages:
  label: Languages
  tab: General
  hint: 'Users who speak these languages will receive the multicast audio on their devices.'
sipDevices:
  label: 'Phones / SIP devices'
  tab: General
  hint: 'Specific SIP devices that will receive the multicast audio, regardless of user targeting rules.'
```