n in the network. NT (Notification Type) headers, defined in GENA, specify the device and its services. Multiple NOTIFY messages are sent to advertise *In the messages, a typesetting face and an italics face show keywords and actual parameters for a UPnP and SIP message, respectively. A bold face in a SIP message shows the same parameters as ones in the corresponding UPnP message. © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security service types, device types, and a device identifier, which are described in the NT header, to other devices in the network. The information in the NT header is in the URI form and used in the discovery search phase in Section 7.5.2. The CACHE-CONTROL header specifies how long the device advertisement will continue. The USN (Unique Service Name), header is a unique identifier defined by SSDP. NOTIFY * HTTP/1.1 HOST: address and port for multicast CACHE-CONTROL: max-age = seconds until advertisement Expires LOCATION: URL for UPnP description for root device NT: search target NTS: ssdp:alive SERVER: OS/version UPnP/1.0 product/version USN: advertisement UUID A discovery advertisement in UPnP corresponds to registration in SIP. When a device joins a network, it sends a REGISTER message to a SIP registry server. In the context of UPnP, a REGISTER message contains the following headers. Note that a text in bold in the SIP message matches a corresponding field with identical text in the UPnP message. The from and to headers show the unique identifier of the registering, or advertised, device. In the contact headers, the search targets of NT headers in the multiple NOTIFY message can be found because the contact header in a single REGISTER message shows an actual address that can be searched for in SIP. REGISTER SIP URI of registry server To: advertisement UUID From: advertisement UUID Expire: seconds until advertisement expires Call-ID: call identifier CSeq: sequence number NTS: ssdp :alive Contact: search target1; host = OS/version UPnP/1.0 product/versi