on; location = URL for UPnP description for root device, search target2; host = OS/version UPnP/1.0 product/version; location = URL for UPnP description for root device When a device leaves the home network, the following ssdp:byebye message is sent to devices in the UPnP network. NOTIFY * HTTP/1, 1 HOST: address and port for multicast NT: search target © 2009 by Taylor & Francis Group, LLC Home Networking System with SIP NTS: ssdp : byebye USN: advertisement UUID The corresponding operation in SIP is cancellation of registration. To can- cel its registration, a device sends the following REGISTER message with an Expire header zero to the registry server. REGISTER SIP URI of registry server To: advertisement UUID From: advertisement UUID Expire: 0 Call-ID: call identifier CSeq: sequence number NTS: ssdp :byebye Contact: search target 7.5.2 Discovery: Search In the discovery advertisement phase of UPnP, a control point multicasts a message as shown below, allowing the control point to search for a device of interest. Note that the ST header here corresponds to the NT header in the discovery advertisement message. When a device receives an M-SEARCH message with its own uid as the search target, it responds with an OK message to the control point. M-SEARCH * HTTP/1.1 HOST: address and port for multicast MAN: ssdp:discover MX: seconds to delay response ST: search target In SIP, a device of interest is searched for with an INVITE message. When a VoIP client requires a certain person, an INVITE message is sent to a registry server and an actual connection destination is searched for using the contact data. In this redesign, an INVITE message with search target data is used to search for a device of interest. To add this search target information, we need to extend the a field in the SDP. An attribute with a prefix X-upnp is an extension attribute for UPnP. For example, the X-upnp: st attributed speci- fies search targets in the M-SEARCH UPnP message. INVITE advertisement UUID To: SIP URL of registry server From: reques