A first wireless device transmits to a second wireless device, a SIP REGISTER message comprising a first Contact header field comprising an internet Protocol multimedia subsystem (IMS) identifier identifying a mission critical video capability of the first wireless device. The second wireless device transmits to an IMS network entity, a second SIP REGISTER message comprising a second Contact header field comprising the IMS identifier. The IMS network entity identifies a mission critical application server (MC AS) and registers the first wireless device to the MC AS. The MC AS: receives a SIP request from the IMS network entity for the first wireless device; determines that a mission critical video service can be established employing the SIP request and the mission critical video capability; and transmits the SIP request to the first wireless device via the second wireless device.