What it does

Companion devices are VoLTE UEs that are linked to a primary device such as a smart phone. Smart watches are a common type of companion device. The companion device service enables companion devices to share a phone number with the primary device. This means:

  • calls to the shared number will cause both devices to ring, and

  • calls from the companion device will appear to come from the shared number.

This type of service is sometimes referred to as "One Number", "Multi-SIM", or "Multi-Device".

The companion device will still have its own number called the "undisclosed identity". Depending on service configuration, it may still be possible to use this number to contact the companion device, but the Rhino VoLTE TAS will always attempt to hide and replace it with the shared number.

The companion device service can function for devices connecting over both packet switched (PS) and circuit switched (CS) networks.

Outbound calls

For outbound calls, the companion device will usually use the shared number to identify itself. However, if it uses its undisclosed identity instead, the companion device service will replace it with the shared number before allowing the call to proceed.

Inbound calls

When an incoming call is targeted at the shared number, the companion device service will force the T-ADS service to use parallel routing mode. This ensures that both the primary and companion device will ring at the same time, regardless of whether they are connected to a PS or CS network. When the subscriber answers the call on either device, the other device will stop ringing.

When companion devices are in use, T-ADS may use special handling if one of the devices indicates the subscriber is busy. If the release-all-legs-on-busy field in the T-ADS configuration is set to true, a single busy response from either device will cause the call to be terminated. If the field is false, T-ADS will wait for a response from the other device as per normal behavior.

The companion device service can also be configured to block incoming calls to the undisclosed identity.

Companion device provisioning

Per-subscriber companion device data is provisioned in two places:

  • IMS subscription data in the HSS, and

  • the Metaswitch-TAS-Services document stored in HSS transparent data.

Provisioning of IMS subscription data is not done using the Rhino VoLTE TAS. Contact your HSS provider for more information.


For standard Rhino VoLTE TAS deployments, the Metaswitch-TAS-Services document is disabled. This must be enabled to activate the companion device service.

Further information on configuring the companion device service subscriber data is given in the managing companion device subscriber data page.

Interactions with other services

Terminating Access Domain Selection (T-ADS)

When a companion device is in use, the companion device service will force the T-ADS service to use its parallel routing mode. However, restrictions imposed by the Request-Disposition header will still apply. See Request disposition in the T-ADS section for details.

The companion device service may also provide CS routing numbers (CSRNs) for the T-ADS service to use on its CS network connection attempts.

CAP charging

If CAP charging is in use, on inbound calls there will be a separate session between the Rhino VoLTE TAS and the service control point (SCP) providing the charging service for each forked PS and CS leg for each device. The leg that is answered by the called subscriber will be charged, and the other legs will be recorded as zero length calls with the SCP.

PSAP callback

Certain functions of the companion device service that could interfere with emergency calls are disabled when an emergency call is detected:

  • When a companion device initiates an emergency call, its undisclosed identity will not be hidden.

  • When a PSAP callback attempt is made to the undisclosed identity, the companion device service will not block the call.


Currently, the declarative configuration for the companion device service is only available through low-level overrides, which require the guidance of Metaswitch support.

To configure the service, contact your Metaswitch customer care representative.

Note Full declarative configuration support for this service may become available in a later version.
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Rhino VoLTE TAS Version 4.0.0