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Sipping Workgroup RFCs

Browse Sipping Workgroup RFCs by Number

RFC3324 - Short Term Requirements for Network Asserted Identity
RFC3351 - User Requirements for the Session Initiation Protocol (SIP) in Support of Deaf, Hard of Hearing and Speech-impaired Individuals
RFC3372 - Session Initiation Protocol for Telephones (SIP-T): Context and Architectures
RFC3398 - Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping
RFC3485 - The Session Initiation Protocol (SIP) and Session Description Protocol (SDP) Static Dictionary for Signaling Compression (SigComp)
The Session Initiation Protocol (SIP) is a text-based protocol for initiating and managing communication sessions. The protocol can be compressed by using Signaling Compression (SigComp). Similarly, the Session Description Protocol (SDP) is a text-based protocol intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. This memo defines the SIP/SDP-specific static dictionary that SigComp may use in order to achieve higher efficiency. The dictionary is compression algorithm independent. [STANDARDS-TRACK]
RFC3578 - Mapping of Integrated Services Digital Network (ISDN) User Part (ISUP) Overlap Signalling to the Session Initiation Protocol (SIP)
This document describes a way to map Integrated Services Digital Network User Part (ISUP) overlap signalling to Session Initiation Protocol (SIP). This mechanism might be implemented when using SIP in an environment where part of the call involves interworking with the Public Switched Telephone Network (PSTN). [STANDARDS-TRACK]
RFC3665 - Session Initiation Protocol (SIP) Basic Call Flow Examples
This document gives examples of Session Initiation Protocol (SIP) call flows. Elements in these call flows include SIP User Agents and Clients, SIP Proxy and Redirect Servers. Scenarios include SIP Registration and SIP session establishment. Call flow diagrams and message details are shown.
RFC3666 - Session Initiation Protocol (SIP) Public Switched Telephone Network (PSTN) Call Flows
This document contains best current practice examples of Session Initiation Protocol (SIP) call flows showing interworking with the Public Switched Telephone Network (PSTN). Elements in these call flows include SIP User Agents, SIP Proxy Servers, and PSTN Gateways. Scenarios include SIP to PSTN, PSTN to SIP, and PSTN to PSTN via SIP. PSTN telephony protocols are illustrated using ISDN (Integrated Services Digital Network), ISUP (ISDN User Part), and FGB (Feature Group B) circuit associated signaling. PSTN calls are illustrated using global telephone numbers from the PSTN and private extensions served on by a PBX (Private Branch Exchange). Call flow diagrams and message details are shown.
RFC3680 - A Session Initiation Protocol (SIP) Event Package for Registrations
This document defines a Session Initiation Protocol (SIP) event package for registrations. Through its REGISTER method, SIP allows a user agent to create, modify, and delete registrations. Registrations can also be altered by administrators in order to enforce policy. As a result, these registrations represent a piece of state in the network that can change dynamically. There are many cases where a user agent would like to be notified of changes in this state. This event package defines a mechanism by which those user agents can request and obtain such notifications. [STANDARDS-TRACK]
RFC3702 - Authentication, Authorization, and Accounting Requirements for the Session Initiation Protocol (SIP)
As Session Initiation Protocol (SIP) services are deployed on the Internet, there is a need for authentication, authorization, and accounting of SIP sessions. This document sets out the basic requirements for this work. This memo provides information for the Internet community.
RFC3725 - Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)
Third party call control refers to the ability of one entity to create a call in which communication is actually between other parties. Third party call control is possible using the mechanisms specified within the Session Initiation Protocol (SIP). However, there are several possible approaches, each with different benefits and drawbacks. This document discusses best current practices for the usage of SIP for third party call control. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
RFC3824 - Using E.164 numbers with the Session Initiation Protocol (SIP)
There are a number of contexts in which telephone numbers are employed by Session Initiation Protocol (SIP) applications, many of which can be addressed by ENUM. Although SIP was one of the primary applications for which ENUM was created, there is nevertheless a need to define procedures for integrating ENUM with SIP implementations. This document illustrates how the two protocols might work in concert, and clarifies the authoring and processing of ENUM records for SIP applications. It also provides guidelines for instances in which ENUM, for whatever reason, cannot be used to resolve a telephone number. This memo provides information for the Internet community.
RFC3842 - A Message Summary and Message Waiting Indication Event Package for the Session Initiation Protocol (SIP)
This document describes a Session Initiation Protocol (SIP) event package to carry message waiting status and message summaries from a messaging system to an interested User Agent. [STANDARDS-TRACK]
RFC3959 - The Early Session Disposition Type for the Session Initiation Protocol (SIP)
This document defines a new disposition type (early-session) for the Content-Disposition header field in the Session Initiation Protocol (SIP). The treatment of "early-session" bodies is similar to the treatment of "session" bodies. That is, they follow the offer/answer model. Their only difference is that session descriptions whose disposition type is "early-session" are used to establish early media sessions within early dialogs, as opposed to regular sessions within regular dialogs. [STANDARDS-TRACK]
RFC3960 - Early Media and Ringing Tone Generation in the Session Initiation Protocol (SIP)
This document describes how to manage early media in the Session Initiation Protocol (SIP) using two models: the gateway model and the application server model. It also describes the inputs one needs to consider in defining local policies for ringing tone generation. This memo provides information for the Internet community.
RFC4083 - Input 3rd-Generation Partnership Project (3GPP) Release 5 Requirements on the Session Initiation Protocol (SIP)
The 3rd-Generation Partnership Project (3GPP) has selected Session Initiation Protocol (SIP) as the session establishment protocol for the 3GPP IP Multimedia Core Network Subsystem (IMS). IMS is part of Release 5 of the 3GPP specifications. Although SIP is a protocol that fulfills most of the requirements for establishing a session in an IP network, SIP has never been evaluated against the specific 3GPP requirements for operation in a cellular network. In this document, we express the requirements identified by 3GPP to support SIP for Release 5 of the 3GPP IMS in cellular networks. This memo provides information for the Internet community.
RFC4117 - Transcoding Services Invocation in the Session Initiation Protocol (SIP) Using Third Party Call Control (3pcc)
This document describes how to invoke transcoding services using Session Initiation Protocol (SIP) and third party call control. This way of invocation meets the requirements for SIP regarding transcoding services invocation to support deaf, hard of hearing and speech-impaired individuals. This memo provides information for the Internet community.
RFC4189 - Requirements for End-to-Middle Security for the Session Initiation Protocol (SIP)
A Session Initiation Protocol (SIP) User Agent (UA) does not always trust all intermediaries in its request path to inspect its message bodies and/or headers contained in its message. The UA might want to protect the message bodies and/or headers from intermediaries, except those that provide services based on its content. This situation requires a mechanism called "end-to-middle security" to secure the information passed between the UA and intermediaries, which does not interfere with end-to-end security. This document defines a set of requirements for a mechanism to achieve end-to-middle security. This memo provides information for the Internet community.
RFC4235 - An INVITE-Initiated Dialog Event Package for the Session Initiation Protocol (SIP)
This document defines a dialog event package for the SIP Events architecture, along with a data format used in notifications for this package. The dialog package allows users to subscribe to another user and to receive notification of the changes in state of INVITE-initiated dialog usages in which the subscribed-to user is involved. [STANDARDS-TRACK]
RFC4245 - High-Level Requirements for Tightly Coupled SIP Conferencing
This document examines a wide range of conferencing requirements for tightly coupled SIP conferences. Separate documents will map the requirements to existing protocol primitives, define new protocol extensions, and introduce new protocols as needed. Together, these documents will provide a guide for building interoperable SIP conferencing applications. This memo provides information for the Internet community.
RFC4353 - A Framework for Conferencing with the Session Initiation Protocol (SIP)
The Session Initiation Protocol (SIP) supports the initiation, modification, and termination of media sessions between user agents. These sessions are managed by SIP dialogs, which represent a SIP relationship between a pair of user agents. Because dialogs are between pairs of user agents, SIP's usage for two-party communications (such as a phone call), is obvious. Communications sessions with multiple participants, generally known as conferencing, are more complicated. This document defines a framework for how such conferencing can occur. This framework describes the overall architecture, terminology, and protocol components needed for multi-party conferencing. This memo provides information for the Internet community.
RFC4411 - Extending the Session Initiation Protocol (SIP) Reason Header for Preemption Events
This document proposes an IANA Registration extension to the Session Initiation Protocol (SIP) Reason Header to be included in a BYE Method Request as a result of a session preemption event, either at a user agent (UA), or somewhere in the network involving a reservation-based protocol such as the Resource ReSerVation Protocol (RSVP) or Next Steps in Signaling (NSIS). This document does not attempt to address routers failing in the packet path; instead, it addresses a deliberate tear down of a flow between UAs, and informs the terminated UA(s) with an indication of what occurred. [STANDARDS-TRACK]
RFC4453 - Requirements for Consent-Based Communications in the Session Initiation Protocol (SIP)
The Session Initiation Protocol (SIP) supports communications across many media types, including real-time audio, video, text, instant messaging, and presence. In its current form, it allows session invitations, instant messages, and other requests to be delivered from one party to another without requiring explicit consent of the recipient. Without such consent, it is possible for SIP to be used for malicious purposes, including spam and denial-of-service attacks. This document identifies a set of requirements for extensions to SIP that add consent-based communications. This memo provides information for the Internet community.
RFC4475 - Session Initiation Protocol (SIP) Torture Test Messages
This informational document gives examples of Session Initiation Protocol (SIP) test messages designed to exercise and "torture" a SIP implementation. This memo provides information for the Internet community.
RFC4484 - Trait-Based Authorization Requirements for the Session Initiation Protocol (SIP)
This document lays out a set of requirements related to trait-based authorization for the Session Initiation Protocol (SIP). While some authentication mechanisms are described in the base SIP specification, trait-based authorization provides information used to make policy decisions based on the attributes of a participant in a session. This approach provides a richer framework for authorization, as well as allows greater privacy for users of an identity system. This memo provides information for the Internet community.
RFC4497 - Interworking between the Session Initiation Protocol (SIP) and QSIG
This document specifies interworking between the Session Initiation Protocol (SIP) and QSIG within corporate telecommunication networks (also known as enterprise networks). SIP is an Internet application-layer control (signalling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include, in particular, telephone calls. QSIG is a signalling protocol for creating, modifying, and terminating circuit-switched calls (in particular, telephone calls) within Private Integrated Services Networks (PISNs). QSIG is specified in a number of Ecma Standards and published also as ISO/IEC standards. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
RFC4569 - Internet Assigned Number Authority (IANA) Registration of the Message Media Feature Tag
This document registers with the IANA a new media feature tag associated with the 'message' media type. This media feature tag indicates that a particular device supports 'message' as a streaming media type. Media feature tags can be used to route calls to devices that support certain features. This memo provides information for the Internet community.
RFC4575 - A Session Initiation Protocol (SIP) Event Package for Conference State
This document defines a conference event package for tightly coupled conferences using the Session Initiation Protocol (SIP) events framework, along with a data format used in notifications for this package. The conference package allows users to subscribe to a conference Uniform Resource Identifier (URI). Notifications are sent about changes in the membership of this conference and optionally about changes in the state of additional conference components. [STANDARDS-TRACK]
RFC4579 - Session Initiation Protocol (SIP) Call Control - Conferencing for User Agents
This specification defines conferencing call control features for the Session Initiation Protocol (SIP). This document builds on the Conferencing Requirements and Framework documents to define how a tightly coupled SIP conference works. The approach is explored from the perspective of different user agent (UA) types: conference-unaware, conference-aware, and focus UAs. The use of Uniform Resource Identifiers (URIs) in conferencing, OPTIONS for capabilities discovery, and call control using REFER are covered in detail with example call flow diagrams. The usage of the isfocus feature tag is defined. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
RFC4596 - Guidelines for Usage of the Session Initiation Protocol (SIP) Caller Preferences Extension
This document contains guidelines for usage of the Caller Preferences Extension to the Session Initiation Protocol (SIP). It demonstrates the benefits of caller preferences with specific example applications, provides use cases to show proper operation, provides guidance on the applicability of the registered feature tags, and describes a straightforward implementation of the preference and capability matching algorithm specified in Section 7.2 of RFC 3841. This memo provides information for the Internet community.
RFC4730 - A Session Initiation Protocol (SIP) Event Package for Key Press Stimulus (KPML)
This document describes a SIP Event Package "kpml" that enables monitoring of Dual Tone Multi-Frequency (DTMF) signals and uses Extensible Markup Language (XML) documents referred to as Key Press Markup Language (KPML). The kpml Event Package may be used to support applications consistent with the principles defined in the document titled "A Framework for Application Interaction in the Session Initiation Protocol (SIP)". The event package uses SUBSCRIBE messages and allows for XML documents that define and describe filter specifications for capturing key presses (DTMF Tones) entered at a presentation-free User Interface SIP User Agent (UA). The event package uses NOTIFY messages and allows for XML documents to report the captured key presses (DTMF tones), consistent with the filter specifications, to an Application Server. The scope of this package is for collecting supplemental key presses or mid-call key presses (triggers). [STANDARDS-TRACK]
RFC5039 - The Session Initiation Protocol (SIP) and Spam
Spam, defined as the transmission of bulk unsolicited messages, has plagued Internet email. Unfortunately, spam is not limited to email. It can affect any system that enables user-to-user communications. The Session Initiation Protocol (SIP) defines a system for user-to- user multimedia communications. Therefore, it is susceptible to spam, just as email is. In this document, we analyze the problem of spam in SIP. We first identify the ways in which the problem is the same and the ways in which it is different from email. We then examine the various possible solutions that have been discussed for email and consider their applicability to SIP. This memo provides information for the Internet community.
RFC5057 - Multiple Dialog Usages in the Session Initiation Protocol
Several methods in the Session Initiation Protocol (SIP) can create an association between endpoints known as a dialog. Some of these methods can also create a different, but related, association within an existing dialog. These multiple associations, or dialog usages, require carefully coordinated processing as they have independent life-cycles, but share common dialog state. Processing multiple dialog usages correctly is not completely understood. What is understood is difficult to implement.
This memo argues that multiple dialog usages should be avoided. It discusses alternatives to their use and clarifies essential behavior for elements that cannot currently avoid them.
This is an informative document and makes no normative statements of any kind. This memo provides information for the Internet community.
RFC5118 - Session Initiation Protocol (SIP) Torture Test Messages for Internet Protocol Version 6 (IPv6)
This document provides examples of Session Initiation Protocol (SIP) test messages designed to exercise and "torture" the code of an IPv6-enabled SIP implementation. This memo provides information for the Internet community.
RFC5194 - Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP)
This document lists the essential requirements for real-time Text-over-IP (ToIP) and defines a framework for implementation of all required functions based on the Session Initiation Protocol (SIP) and the Real-Time Transport Protocol (RTP). This includes interworking between Text-over-IP and existing text telephony on the Public Switched Telephone Network (PSTN) and other networks. This memo provides information for the Internet community.
RFC5359 - Session Initiation Protocol Service Examples
This document gives examples of Session Initiation Protocol (SIP) services. This covers most features offered in so-called IP Centrex offerings from local exchange carriers and PBX (Private Branch Exchange) features. Most of the services shown in this document are implemented in the SIP user agents, although some require the assistance of a SIP proxy. Some require some extensions to SIP including the REFER, SUBSCRIBE, and NOTIFY methods and the Replaces and Join header fields. These features are not intended to be an exhaustive set, but rather show implementations of common features likely to be implemented on SIP IP telephones in a business environment. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
RFC5361 - A Document Format for Requesting Consent
This document defines an Extensible Markup Language (XML) format for a permission document used to request consent. A permission document written in this format is used by a relay to request a specific recipient permission to perform a particular routing translation. [STANDARDS-TRACK]
RFC5362 - The Session Initiation Protocol (SIP) Pending Additions Event Package
This document defines the SIP Pending Additions event package. This event package is used by SIP relays to inform user agents about the consent-related status of the entries to be added to a resource list. [STANDARDS-TRACK]
RFC5363 - Framework and Security Considerations for Session Initiation Protocol (SIP) URI-List Services
This document describes the need for SIP URI-list services and provides requirements for their invocation. Additionally, it defines a framework for SIP URI-list services, which includes security considerations applicable to these services. [STANDARDS-TRACK]
RFC5364 - Extensible Markup Language (XML) Format Extension for Representing Copy Control Attributes in Resource Lists
In certain types of multimedia communications, a Session Initiation Protocol (SIP) request is distributed to a group of SIP User Agents (UAs). The sender sends a single SIP request to a server which further distributes the request to the group. This SIP request contains a list of Uniform Resource Identifiers (URIs), which identify the recipients of the SIP request. This URI list is expressed as a resource list XML document. This specification defines an XML extension to the XML resource list format that allows the sender of the request to qualify a recipient with a copy control level similar to the copy control level of existing email systems. [STANDARDS-TRACK]
RFC5369 - Framework for Transcoding with the Session Initiation Protocol (SIP)
This document defines a framework for transcoding with SIP. This framework includes how to discover the need for transcoding services in a session and how to invoke those transcoding services. Two models for transcoding services invocation are discussed: the conference bridge model and the third-party call control model. Both models meet the requirements for SIP regarding transcoding services invocation to support deaf, hard of hearing, and speech-impaired individuals. This memo provides information for the Internet community.
RFC5370 - The Session Initiation Protocol (SIP) Conference Bridge Transcoding Model
This document describes how to invoke transcoding services using the conference bridge model. This way of invocation meets the requirements for SIP regarding transcoding services invocation to support deaf, hard of hearing, and speech-impaired individuals. [STANDARDS-TRACK]
RFC5390 - Requirements for Management of Overload in the Session Initiation Protocol
Overload occurs in Session Initiation Protocol (SIP) networks when proxies and user agents have insufficient resources to complete the processing of a request. SIP provides limited support for overload handling through its 503 response code, which tells an upstream element that it is overloaded. However, numerous problems have been identified with this mechanism. This document summarizes the problems with the existing 503 mechanism, and provides some requirements for a solution. This memo provides information for the Internet community.
RFC5407 - Example Call Flows of Race Conditions in the Session Initiation Protocol (SIP)
This document gives example call flows of race conditions in the Session Initiation Protocol (SIP). Race conditions are inherently confusing and difficult to thwart; this document shows the best practices to handle them. The elements in these call flows include SIP User Agents and SIP Proxy Servers. Call flow diagrams and message details are given. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.
RFC5628 - Registration Event Package Extension for Session Initiation Protocol (SIP) Globally Routable User Agent URIs (GRUUs)
RFC 3680 defines a Session Initiation Protocol (SIP) event package for registration state. This package allows a watcher to learn about information stored by a SIP registrar, including its registered contact.
However, the registered contact is frequently unreachable and thus not useful for watchers. The Globally Routable User Agent URI (GRUU), defined in RFC 5627, is a URI that is capable of reaching a particular contact. However this URI is not included in the document format defined in RFC 3680. This specification defines an extension to the registration event package to include GRUUs assigned by the registrar. [STANDARDS-TRACK]
RFC5629 - A Framework for Application Interaction in the Session Initiation Protocol (SIP)
This document describes a framework for the interaction between users and Session Initiation Protocol (SIP) based applications. By interacting with applications, users can guide the way in which they operate. The focus of this framework is stimulus signaling, which allows a user agent (UA) to interact with an application without knowledge of the semantics of that application. Stimulus signaling can occur to a user interface running locally with the client, or to a remote user interface, through media streams. Stimulus signaling encompasses a wide range of mechanisms, ranging from clicking on hyperlinks, to pressing buttons, to traditional Dual-Tone Multi- Frequency (DTMF) input. In all cases, stimulus signaling is supported through the use of markup languages, which play a key role in this framework. [STANDARDS-TRACK]
RFC5850 - A Call Control and Multi-Party Usage Framework for the Session Initiation Protocol (SIP)
This document defines a framework and the requirements for call control and multi-party usage of the Session Initiation Protocol (SIP). To enable discussion of multi-party features and applications, we define an abstract call model for describing the media relationships required by many of these. The model and actions described here are specifically chosen to be independent of the SIP signaling and/or mixing approach chosen to actually set up the media relationships. In addition to its dialog manipulation aspect, this framework includes requirements for communicating related information and events such as conference and session state and session history. This framework also describes other goals that embody the spirit of SIP applications as used on the Internet such as the definition of primitives (not services), invoker and participant oriented primitives, signaling and mixing model independence, and others. This document is not an Internet Standards Track specification; it is published for informational purposes.
RFC5853 - Requirements from Session Initiation Protocol (SIP) Session Border Control (SBC) Deployments
This document describes functions implemented in Session Initiation Protocol (SIP) intermediaries known as Session Border Controllers (SBCs). The goal of this document is to describe the commonly provided functions of SBCs. A special focus is given to those practices that are viewed to be in conflict with SIP architectural principles. This document also explores the underlying requirements of network operators that have led to the use of these functions and practices in order to identify protocol requirements and determine whether those requirements are satisfied by existing specifications or if additional standards work is required. This document is not an Internet Standards Track specification; it is published for informational purposes.
RFC5876 - Updates to Asserted Identity in the Session Initiation Protocol (SIP)
The Session Initiation Protocol (SIP) has a mechanism for conveying the identity of the originator of a request by means of the P-Asserted-Identity and P-Preferred-Identity header fields. These header fields are specified for use in requests using a number of SIP methods, in particular the INVITE method. However, RFC 3325 does not specify the insertion of the P-Asserted-Identity header field by a trusted User Agent Client (UAC), does not specify the use of P-Asserted-Identity and P-Preferred-Identity header fields with certain SIP methods such as UPDATE, REGISTER, MESSAGE, and PUBLISH, and does not specify how to handle an unexpected number of URIs or unexpected URI schemes in these header fields. This document extends RFC 3325 to cover these situations. This document is not an Internet Standards Track specification; it is published for informational purposes.
RFC5897 - Identification of Communications Services in the Session Initiation Protocol (SIP)
This document considers the problem of service identification in the Session Initiation Protocol (SIP). Service identification is the process of determining the user-level use case that is driving the signaling being utilized by the user agent (UA). This document discusses the uses of service identification, and outlines several architectural principles behind the process. It identifies perils when service identification is not done properly -- including fraud, interoperability failures, and stifling of innovation. It then outlines a set of recommended practices for service identification. This document is not an Internet Standards Track specification; it is published for informational purposes.
RFC6035 - Session Initiation Protocol Event Package for Voice Quality Reporting
This document defines a Session Initiation Protocol (SIP) event package that enables the collection and reporting of metrics that measure the quality for Voice over Internet Protocol (VoIP) sessions. Voice call quality information derived from RTP Control Protocol Extended Reports (RTCP-XR) and call information from SIP is conveyed from a User Agent (UA) in a session, known as a reporter, to a third party, known as a collector. A registration for the application/ vq-rtcpxr media type is also included. [STANDARDS-TRACK]
RFC6080 - A Framework for Session Initiation Protocol User Agent Profile Delivery
This document specifies a framework to enable configuration of Session Initiation Protocol (SIP) user agents (UAs) in SIP deployments. The framework provides a means to deliver profile data that user agents need to be functional, automatically and with minimal or no User and Administrative intervention. The framework describes how SIP user agents can discover sources, request profiles, and receive notifications related to profile modifications. As part of this framework, a new SIP event package is defined for notification of profile changes. The framework provides minimal data retrieval options to ensure interoperability. The framework does not include specification of the profile data within its scope. [STANDARDS-TRACK]
RFC6157 - IPv6 Transition in the Session Initiation Protocol (SIP)
This document describes how the IPv4 Session Initiation Protocol (SIP) user agents can communicate with IPv6 SIP user agents (and vice versa) at the signaling layer as well as exchange media once the session has been successfully set up. Both single- and dual-stack (i.e., IPv4-only and IPv4/IPv6) user agents are considered. [STANDARDS-TRACK]
RFC6795 - A Session Initiation Protocol (SIP) Event Package for Session-Specific Policies
This specification defines a Session Initiation Protocol (SIP) event package for session-specific policies. This event package enables user agents (UAs) to subscribe to session policies for a SIP session and to receive notifications if these policies change. [STANDARDS-TRACK]