e V= field contains the SDP version number. Because the current version of SDP is 0, a valid SDP message will always begin with v=0. 7.1.2 Origin The O= field contains information about the originator of the session and ses- sion identifiers. This field is used to uniquely identify the session. The field contains: SIP: Understanding the Session Initiation Protocol O=username session-id version network-type address-type address The username parameter contains the originator's login or host or - if none. The session-id parameter is a Network Time Protocol (NTP) [3] timestamp or a random number used to ensure uniqueness. The version is a numeric field that is increased for each change to the session, also recommended to be a NTP timestamp. The network-type is always IN for Internet. The address-type parameter is either IP4 or IP6 for IPv4 or IPv6 address either in dotted decimal form or a fully qualified host name. 7.1.3 Session Name and Information The S= field contains a name for the session. It can contain any non-zero number of characters. The optional i= field contains information about the session. It can contain any number of characters. 7.1.4 The optional u= field contains a uniform resource indicator (URI) with more information about the session. 7.1.5 E-Mail Address and Phone Number The optional e= field contains an e-mail address of the host of the session. If a display name is used, the e-mail address is enclosed in <>. The optional p field contains a phone number. The phone number should be given in globalized for- mat, beginning with a +, then the country code, a space or -, then the local number. Either spaces or - are permitted as spacers in SDP. A comment may be present in (). 7.1.6 Connection Data The C= field contains information about the media connection. The field contains: c=network-type address-type connection-address The network-type parameter is defined as IN for the Internet. The address type is defined as IP4 for IPv4 addresses, IP6 for IPv6 addresses. The connection-address is the IP add