d in date form rather than second count to be easily converted into delta seconds without requiring knowledge of time zone offsets. A Date example is shown here: Date: Fri, 13 Oct 1998 23:29:00 GMT 6.1.7 Encryption The Encryption header field was defined in RFC 2543 but is not included in RFC 3261. Instead, encryption using S/MIME is defined as discussed in Section 3.9. 6.1.8 From The From header field is a required header field that indicates the originator of the request. It is one of two addresses used to identify the dialog. The From header field contains a URI, but it may not contain the transport, maddr, or ttl URI parameters. A From header field may contain a tag, used to identify a particular call. A From header field may contain a display name, in which case the URI is enclosed in < >. If there is both a URI parameter and a tag, then the URI including any parameters must be enclosed in < >. Examples are shown in Table 6.6. A From tag was optional in RFC 2543 but is mandatory to include in RFC 3261. SIP: Understanding the Session Initiation Protocol Table 6.6 Examples of From Header Field Header Field Meaning From: <sip armstrong@hetrodyne.com: A single SIP URI with a tag ; tag=3342436 From: Thomas Edison A secure SIP URI with a display name <sips: edison@electric.com>;tag=532 f: "James Bardeen" Using the compact form of the header <sip: 555.1313@telephone.com field, a display name in quotes along transport=tcp>;tag=3a320f03 with a SIP URI with a parameter inside the < >. From: tel:911 A tel URI without a display name or tag, so no <> is required. Generated by a RFC 2543 UA 6.1.9 Organization The Organization header field is used to indicate the organization to which the originator of the message belongs. It can also be inserted by proxies as a message is passed from one organization to another. Like all SIP header fields, it can be used by proxies for making routing decisions and by user agents for making call screening decisions. An example is below: Organization: MCI 6.1.10 Record-Route The Record-Rout