javax.sip.header

Interface FromHeader

All Superinterfaces:

Cloneable, Header, HeaderAddress, Parameters, Serializable

All Known Implementing Classes:

From

public interface FromHeader
extends HeaderAddress, Parameters, Header

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 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:[email protected]), 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" sips:[email protected] ;tag=a48s
From: sip:[email protected];tag=887s
From: Anonymous sip:[email protected];tag=hyh8

Version:

1.2

Author:

BEA Systems, NIST

Field Summary

Fields

Modifier and Type	Field and Description
static String	NAME Name of FromHeader

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(Object obj) Compare this FromHeader for equality with another.
String	getTag() Gets the tag of FromHeader.
void	setTag(String tag) Sets the tag parameter of the FromHeader.

Methods inherited from interface javax.sip.header.HeaderAddress

getAddress, setAddress

Methods inherited from interface javax.sip.header.Parameters

getParameter, getParameterNames, removeParameter, setParameter

Methods inherited from interface javax.sip.header.Header

clone, getName, hashCode, toString

Field Detail

NAME

static final String NAME

Name of FromHeader

See Also:

Constant Field Values

Method Detail

setTag

void setTag(String tag)
            throws ParseException

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.

Parameters:

tag - - the new tag of the FromHeader

Throws:

ParseException - which signals that an error has been reached unexpectedly while parsing the Tag value.

getTag

String getTag()

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

Returns:

the tag parameter of the FromHeader.

equals

boolean equals(Object obj)

Compare this FromHeader for equality with another. This method overrides the equals method in javax.sip.Header. This method specifies object equality as outlined by RFC3261. 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. When comparing header fields, field names are always case-insensitive. Unless otherwise stated in the definition of a particular header field, field values, parameter names, and parameter values are case-insensitive. Tokens are always case-insensitive. Unless specified otherwise, values expressed as quoted strings are case-sensitive.

Specified by:

equals in interface Header

Overrides:

equals in class Object

Parameters:

obj - the object to compare this FromHeader with.

Returns:

true if obj is an instance of this class representing the same FromHeader as this, false otherwise.

Since:

v1.2