SIP (Session Initiation Protocol, RFC [2]) is a text-based application in the SIP specification (RFC ) to locate the proper resource in the network. RFC Client-Initiated Connections in SIP October the Trust Legal .. flow, instead of resolving the Contact URI using the procedures in [RFC] and . Canonical URL: ; File formats: Plain Text PDF Discuss this RFC: Send questions or comments to [email protected]

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SIP is an exceptionally popular and extensible protocol. The efficient use of network resources, which may include a radio interface or other low-bandwidth ierf, is essential in the IMS in order to provide the user with an acceptable experience in terms of latency. When a client initiates a SIP dialog with a server, it states the extensions it requires to be used and also other extensions that are understood supportedand the server will then send a response with a list of extensions that it requires.

ITU-T A.5 reference justification

This establishment will occur if and only if both the caller and the callee agree that the preconditions are met.

Source routing is the mechanism that allows the sender of a message to specify partially or completely the route the message traverses. By using this site, you agree to the Terms of Use and Privacy Policy.

Moreover, the SIP INFO method extension is designed to carry user information between terminals without affecting the signaling dialog and can be used to transport the dual-tone multi-frequency signaling to provide telephone keypad function for users.

Accept-Contact to describe the desired destination user agents, Reject-Contact to state the user agents to avoid, and Request-Disposition to specify how the request should be handled by servers in the network i. Retrieved December 4, Communicating Presentation Information in Internet Messages: Each kind of event a subscriber can subscribe to is defined in a new event package. Oracle Communications Converged Application Server supports applications that conform to this specification. The Private Header Extensions to SIP, [6] also known as P-Headers, are special header fields whose applicability is limited to private networks with a certain topology and characteristics of lower layers ‘ protocols.


The degree of stability or maturity of the document:.

In order to make an efficient use of the signaling messages, it is also possible to establish a limited notification rate not real-time notifications through a mechanism called event throttling. Likewise, if the server does not support any of the client’s required extensions, it will send an error rtc with a list of its unsupported extensions.

The IMS is meant to provide multimedia services over IP networks, but also needs a mechanism to charge users for it.

In SIP, the route header field, filled by the sender, supports this functionality rfd listing a set of proxies the message will visit. There are several standards that address this requirements, such as the following two for services interworking between the PSTN and the Internet i. There are several mechanisms to achieve this, such as:.

ITU-T work programme

This can be used to negotiate and allocate the call resources before the called party is alerted. Retrieved 15 November The new SDP attributes are meant to describe the current status of the resource reservation, the desired status of the reservation to proceed with session establishment, and the confirmation statusketf indicate when the reservation status should be confirmed.

Event notification is necessary in the IMS framework to inform about the presence of a user i. The functionality of sending instant messages to provide a service similar to text messaging is defined in the instant messaging extension.

RFC – Session Initiation Protocol (SIP): Locating SIP Servers

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. PUBLISH, which is used to request the publication of the state of the resource specified in the request-URI, with reference to the event stated in the Event headerand with the information carried in the message body.


However, as many words are repeated in different messages, the extended operations for SigComp [34] define a way to use a shared dictionary among subsequent messages. Compression algorithms perform this operation by substituting repeated words in the message by its position in a dictionary where all these words only appear once.

In the IMS, the initial session parameter negotiation can be done by using the provisional responses and session description updating extensions, along with SDP in the body of the messages.

Retrieved 3 December Merging the Internet and the Cellular Worlds 3 ed.

SIP extensions for the IP Multimedia Subsystem

In the IMS every user agent is served by rdc 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.

In a first approach, this dictionary may be built for each message by the compressor and sent to the decompressor along with the message itself.

To indicate that the user agent requests or supports reliable provisional responses, the rel option tag will be used. This kind of extensions are called option tagsbut SIP can also be extended with new methods.

PRACK, which is the request message used to tell the sender of a provisional response that his or her message has been received.