The Date header field reflects the time when the request or response is
first sent. Retransmissions have the same Date header field value as the
original. The Date header field contains the date and time. Unlike
HTTP/1.1, SIP only supports the most recent
format for dates.
SIP restricts the time zone in SIP-date to "GMT", while RFC 1123 allows any
The Date header field can be used by simple end systems without a
battery-backed clock to acquire a notion of current time. However, in its
GMT form, it requires clients to know their offset from GMT.
Date: Sat, 13 Nov 2010 23:29:00 GMT
- BEA Systems, NIST