Section: 13.8 Instance-ID
Content: An instance-id is a SIP Contact header parameter that uniquely identifies the SIP UA performing a registration. When an IMEI is available, the instance-id shall take the form of a IMEI URN (see RFC 7254 [79]). The format of the instance-id shall take the form "urn:gsma:imei:<imeival>" where by the imeival shall contain the IMEI encoded as defined in RFC 7254 [79]. The optional <sw-version-param> and <imei-version-param> parameters shall not be included in the instance-id. RFC 7255 [104] specifies additional considerations for using the IMEI as an instance-id. An example of such an instance-id is as follows: EXAMPLE: urn:gsma:imei:90420156-025763-0 If no IMEI is available, the instance-id shall take the form of a string representation of a UUID as a URN as defined in IETF RFC 4122 [80]. An example of such an instance-id is as follows: EXAMPLE: urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 For more information on the instance-id and when it is used, see 3GPP TS 24.229[ IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 ]  [81].