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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Unpublished - rights reserved under the Copyright Laws of the United States. Copyright � 2003 Sun Microsystems, Inc. All rights reserved. U.S. Government Rights - Commercial software. Government users are subject to the Sun Microsystems, Inc. standard license agreement and applicable provisions of the FAR and its supplements. Use is subject to license terms. This distribution may include materials developed by third parties. Sun, Sun Microsystems, the Sun logo, Java, Jini and JAIN are trademarks or registered trademarks of Sun Microsystems, Inc. in the U.S. and other countries. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Module Name : JAIN SIP Specification File Name : Author : Phelim O'Doherty (modified by Peter Musgrave) HISTORY Version Date Author Comments 1.1 08/10/2002 Phelim O'Doherty ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 package gov.nist.javax.sip.header.extensions;
The From header field indicates the logical identity of the initiator of the request, possibly the user's address-of-record. This may be different from the initiator of the dialog. Requests sent by the callee to the caller use the callee's address in the From header field.

Like the To header field, it contains a URI and optionally a display name, encapsulated in a javax.sip.address.Address. It is used by SIP elements to determine which processing rules to apply to a request (for example, automatic call rejection). As such, it is very important that the From URI not contain IP addresses or the FQDN of the host on which the UA is running, since these are not logical names.

The From header field allows for a display name. A UAC SHOULD use the display name "Anonymous", along with a syntactically correct, but otherwise meaningless URI (like sip:thisis@anonymous.invalid), if the identity of the client is to remain hidden.

Usually, the value that populates the From header field in requests generated by a particular UA is pre-provisioned by the user or by the administrators of the user's local domain. If a particular UA is used by multiple users, it might have switchable profiles that include a URI corresponding to the identity of the profiled user. Recipients of requests can authenticate the originator of a request in order to ascertain that they are who their From header field claims they are.

Two From header fields are equivalent if their URIs match, and their parameters match. Extension parameters in one header field, not present in the other are ignored for the purposes of comparison. This means that the display name and presence or absence of angle brackets do not affect matching.

  • The "Tag" parameter - is used in the To and From header fields of SIP messages. It serves as a general mechanism to identify a dialog, which is the combination of the Call-ID along with two tags, one from each participant in the dialog. When a User Agent sends a request outside of a dialog, it contains a From tag only, providing "half" of the dialog ID. The dialog is completed from the response(s), each of which contributes the second half in the To header field. When a tag is generated by a User Agent for insertion into a request or response, it MUST be globally unique and cryptographically random with at least 32 bits of randomness. Besides the requirement for global uniqueness, the algorithm for generating a tag is implementation specific. Tags are helpful in fault tolerant systems, where a dialog is to be recovered on an alternate server after a failure. A UAS can select the tag in such a way that a backup can recognize a request as part of a dialog on the failed server, and therefore determine that it should attempt to recover the dialog and any other state associated with it.
For Example:
From: "Bob" ;tag=a48s
From: Anonymous;tag=hyh8

Sun Microsystems
public interface ReplacesHeader extends ParametersHeader {

Sets the tag parameter of the FromHeader. The tag in the From field of a request identifies the peer of the dialog. When a UA sends a request outside of a dialog, it contains a From tag only, providing "half" of the dialog Identifier.

The From Header MUST contain a new "tag" parameter, chosen by the UAC applicaton. Once the initial From "tag" is assigned it should not be manipulated by the application. That is on the client side for outbound requests the application is responsible for Tag assigmennment, after dialog establishment the stack will take care of Tag assignment.

tag - the new tag of the FromHeader
java.text.ParseException which signals that an error has been reached unexpectedly while parsing the Tag value.
    public void setToTag(String tagthrows ParseException;
    public void setFromTag(String tagthrows ParseException;

Gets the tag of FromHeader. The Tag parameter identified the Peer of the dialogue and must always be present.

the tag parameter of the FromHeader.
    public String getToTag();
    public String getFromTag();

Sets the Call-Id of the CallIdHeader. The CallId parameter uniquely identifies a serious of messages within a dialogue.

callId - the string value of the Call-Id of this CallIdHeader.
java.text.ParseException which signals that an error has been reached unexpectedly while parsing the callId value.
    public void setCallId(String callIdthrows ParseException;

Returns the Call-Id of CallIdHeader. The CallId parameter uniquely identifies a series of messages within a dialogue.

the String value of the Call-Id of this CallIdHeader
    public String getCallId();

Name of FromHeader
    public final static String NAME = "Replaces";
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