these extensions are described in section 4. · RFC A Message Summary and Message Waiting Indication Event Package . Find the most up-to-date version of IETF – RFC at Engineering Find the most up-to-date version of RFC at Engineering
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This kind of extensions are called option tagsbut SIP can also be extended with new methods. There is a mechanism  in 326 for extension negotiation between user agents UA or servers, consisting of three header fields: The event notification framework defines how a user agent can subscribe to events about the state of a resource, but iett does not specify how that state can be published.
Likewise, if the server does not support any of the client’s required extensions, it will send an error response with a list of its unsupported extensions. Event notification is necessary in the IMS framework to inform about the presence of a user i.
In the IMS every user agent is served by its P-CSCF, which is discovered by using the Dynamic Host Configuration Protocol or an equivalent mechanism when the user enters the IMS network, and all requests and responses from or to the user agent must traverse this proxy. An important source of failure is the inability to reserve network resources ieetf support the session, so these resources should be allocated before the phone rings.
When a client initiates a SIP dialog with a server, it states the extensions it requires to be used and also rgc extensions that are understood supportedand the server will then send a response with a list of extensions that it requires. The IMS is meant to provide multimedia services over IP networks, but also needs a mechanism to charge users for it. Other useful information describing the “Quality” of the document:.
The reliability of provisional responses extension  provides a mechanism to confirm that provisional responses such as the Ringing response codethat lets the caller know that the callee is being alerted, are successfully received. Retrieved November 15, RFCs,,,,Errata Exist 7.
SIP and Open Standards
Relationship with other existing or emerging documents: Therefore, a mechanism is needed in order to route requests to the desired device or application. Relationship with other existing or emerging documents:. This way the recipient of the message can decide whether or not to follow the reference to ketf the resource, depending on the bandwidth available.
The SIP extension for event state publication  was defined to allow user agents to publish the state of an event to the entity notifier that is responsible for composing the event state and distributing it to the subscribers.
Therefore, NAT traversal mechanisms are needed for both the signaling plane and the media plane. Other for any supplementary information: The degree of stability or maturity of the document: Other specific requirements are: In the IMS framework it is fundamental ieetf handle user identities for authentication, authorization and accounting purposes. This mechanism is necessary since SIP can run not only over reliable transport protocols TCP that assure that the message is delivered, but also over unreliable ones UDP that offer no delivery guarantees, and it is even possible that both kinds of protocols are present in different parts of the transport network.
Clear description 32265 the referenced document:. To rffc the sender to discover such entities and populate the route header field, there are mainly two extension header fields: The REFER message also implies an event subscription to the result of the operation, so that the sender will know whether or not the recipient could 3256 the third person.
By using the user agent capabilities extension,  user agents terminals can describe themselves when they register so that others can search for them according to their caller preferences extension headers.
In that case, user agents or servers use the Allow header to state which methods they support.
ITU-T work programme
There are several standards that address this requirements, such as the following two for services interworking between the PSTN and the Internet i. Moreover, there is also a mechanism for conditional event notification that allows the notifier to decide whether or not to send the complete NOTIFY message depending on if there is something new to notify since last subscription or there is not.
To obtain transmission resources, the user agent must present an authorization token to the network i. Source routing is the mechanism that allows the sender of a message to specify partially or completely the route the message traverses. Each kind of event a subscriber can subscribe to is defined in a new event package.