X-Msw-Companion-Device header is a custom SIP header used by Sentinel VoLTE when
a companion device may be used on a call.
The terminating MMTel-AS instance inserts this header in the initial INVITE if the served user’s
Metaswitch-TAS-Services transparent data indicates that they have a companion device.
The header conveys this information to the terminating SCC-AS instance.
The T-ADS features in the SCC-AS will use this
information to decide whether the INVITE should be forked to the companion device.
The header name is
X-Msw-Companion-Device, and its value is the radio access type supported by the companion device.
Currently the only supported value is
PS, indicating the subscriber has a companion device supporting packet-switched radio access types, e.g. LTE or WiFi.
Companion device support is an experimental feature, so the header format may change in a future release.