The Expires header field gives the relative time after which the message (or content) expires. The precise meaning of this is method dependent. The expiration time in an INVITE does not affect the duration of the actual session that may result from the invitation. Session description protocols may offer the ability to express time limits on the session duration, however. The value of this field is an integral number of seconds (in decimal) between 0 and (2**32)-1, measured from the receipt of the request. Malformed values SHOULD be treated as equivalent to 3600.
This interface represents the Expires entity-header. The ExpiresHeader is optional in both REGISTER and INVITE Requests.
- REGISTER - When a client sends a REGISTER request, it MAY suggest an expiration interval that indicates how long the client would like the registration to be valid. There are two ways in which a client can suggest an expiration interval for a binding: through an Expires header field or an "expires" Contact header parameter. The latter allows expiration intervals to be suggested on a per-binding basis when more than one binding is given in a single REGISTER request, whereas the former suggests an expiration interval for all Contact header field values that do not contain the "expires" parameter.
- INVITE - The UAC MAY add an Expires header field to limit the validity of the invitation. If the time indicated in the Expires header field is reached and no final answer for the INVITE has been received, the UAC core SHOULD generate a CANCEL request for the INVITE.
Example:
Expires: 5
@author BEA Systems, NIST
@version 1.2