javax.sip.header

Interface ToHeader

All Superinterfaces:

Cloneable, Header, HeaderAddress, Parameters, Serializable

All Known Implementing Classes:

To

public interface ToHeader
extends HeaderAddress, Parameters, Header

The To header field first and foremost specifies the desired "logical" recipient of the request, or the address-of-record of the user or resource that is the target of this request. This may or may not be the ultimate recipient of the request. Requests and Responses must contain a ToHeader, indicating the desired recipient of the Request. The UAS or redirect server copies the ToHeader into its Response.

The To header field MAY contain a SIP or SIPS URI, but it may also make use of other URI schemes i.e the telURL, when appropriate. All SIP implementations MUST support the SIP URI scheme. Any implementation that supports TLS MUST support the SIPS URI scheme. Like the From header field, it contains a URI and optionally a display name, encapsulated in a Address.

A UAC may learn how to populate the To header field for a particular request in a number of ways. Usually the user will suggest the To header field through a human interface, perhaps inputting the URI manually or selecting it from some sort of address book. Using the string to form the user part of a SIP URI implies that the User Agent wishes the name to be resolved in the domain to the right-hand side (RHS) of the at-sign in the SIP URI. Using the string to form the user part of a SIPS URI implies that the User Agent wishes to communicate securely, and that the name is to be resolved in the domain to the RHS of the at-sign. The RHS will frequently be the home domain of the requestor, which allows for the home domain to process the outgoing request. This is useful for features like "speed dial" that require interpretation of the user part in the home domain.

The telURL may be used when the User Agent does not wish to specify the domain that should interpret a telephone number that has been input by the user. Rather, each domain through which the request passes would be given that opportunity. As an example, a user in an airport might log in and send requests through an outbound proxy in the airport. If they enter "411" (this is the phone number for local directory assistance in the United States), that needs to be interpreted and processed by the outbound proxy in the airport, not the user's home domain. In this case, tel:411 would be the right choice.

Two To 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 UA 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 UA 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.

A request outside of a dialog MUST NOT contain a To tag; the tag in the To field of a request identifies the peer of the dialog. Since no dialog is established, no tag is present.

For Example:
To: Carol sip:[email protected]
To: Duke sip:[email protected];tag=287447

Version:

1.2

Author:

BEA Systems, NIST

See Also:

HeaderAddress

Field Summary

Fields

Modifier and Type	Field and Description
static String	NAME Name of the ToHeader

Method Summary

Methods

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

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 the ToHeader

See Also:

Constant Field Values

Method Detail

setTag

void setTag(String tag)
            throws ParseException

Sets the tag parameter of the ToHeader. The tag in the To field of a request identifies the peer of the dialog. If no dialog is established, no tag is present.

The To Header MUST contain a new "tag" parameter. When acting as a UAC the To "tag" is maintained by the SipProvider from the dialog layer, however whan acting as a UAS the To "tag" is assigned by the application. That is the tag assignment for outbound responses for messages in a dialog is only the responsibility of the application for the first outbound response. If AUTOMATIC_DIALOG_SUPPORT is set to on (default behavior) then, after dialog establishment, the stack will take care of the tag assignment. Null is acceptable as a tag value. Supplying null for the tag results in a header without a tag.

Parameters:

tag - - the new tag of the To Header

Throws:

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

getTag

String getTag()

Gets tag of ToHeader. The Tag parameter identified the Peer of the dialogue.

Returns:

the tag parameter of the ToHeader. Returns null if no Tag is present, i.e no dialogue is established.

equals

boolean equals(Object obj)

Compare this ToHeader for equality with another. This method overrides the equals method in javax.sip.Header. This method specifies object equality as outlined by RFC3261. Two To 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 ToHeader with.

Returns:

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

Since:

v1.2