SIPPING J. Rosenberg Internet-Draft dynamicsoft Expires: August 16, 2004 P. Kyzivat Cisco Systems February 16, 2004 Guidelines for Usage of the Session Initiation Protocol (SIP) Caller Preferences Extension draft-ietf-sipping-callerprefs-usecases-01 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 16, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document contains guidelines for usage of the Caller Preferences Extension to the Session Initiation Protocol (SIP). It motivates 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 matching algorithm. Rosenberg & Kyzivat Expires August 16, 2004 [Page 1] Internet-Draft Caller Preferences Uses February 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4 2. Motivations for Caller Preferences . . . . . . . . . . . . 5 2.1 One-Number . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Direct-to-Voicemail . . . . . . . . . . . . . . . . . . . 7 3. Caller Preference Use Cases . . . . . . . . . . . . . . . 9 3.1 Routing of INVITE and MESSAGE to different UA . . . . . . 9 3.1.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 9 3.1.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2 Single Contact Not Matching Implicit Preferences . . . . . 10 3.2.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 10 3.2.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3 Package-Based Routing . . . . . . . . . . . . . . . . . . 11 3.3.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 11 3.3.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.4 Package Routing II . . . . . . . . . . . . . . . . . . . . 13 3.4.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 13 3.4.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.5 Audio/Video vs. Audio Only . . . . . . . . . . . . . . . . 13 3.5.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 13 3.5.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.6 Forcing Audio/Video . . . . . . . . . . . . . . . . . . . 15 3.6.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 15 3.6.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.7 Third Party Call Control - Forcing Media . . . . . . . . . 16 3.7.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 16 3.7.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.8 Maximizing Media Overlaps . . . . . . . . . . . . . . . . 17 3.8.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 17 3.8.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.9 Multilingual Lines . . . . . . . . . . . . . . . . . . . . 19 3.9.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 19 3.9.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.10 I Hate Voicemail! . . . . . . . . . . . . . . . . . . . . 20 3.10.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 20 3.10.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.11 I Hate People! . . . . . . . . . . . . . . . . . . . . . . 21 3.11.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 22 3.11.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.12 Prefer Voicemail . . . . . . . . . . . . . . . . . . . . . 22 3.12.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 22 3.12.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.13 Routing to an Executive . . . . . . . . . . . . . . . . . 22 3.13.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 22 3.13.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.14 Speak to the Executive . . . . . . . . . . . . . . . . . . 24 3.14.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 24 Rosenberg & Kyzivat Expires August 16, 2004 [Page 2] Internet-Draft Caller Preferences Uses February 2004 3.14.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.15 Mobile Phone Only . . . . . . . . . . . . . . . . . . . . 24 3.15.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 24 3.15.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.16 Simultaneous Languages . . . . . . . . . . . . . . . . . . 25 3.16.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 25 3.16.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.17 UA Routing . . . . . . . . . . . . . . . . . . . . . . . . 26 3.17.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 26 3.17.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.18 The Number you Have Called.. . . . . . . . . . . . . . . . 27 3.18.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 27 3.18.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.19 The Number you Have Called, Take Two . . . . . . . . . . . 29 3.19.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 29 3.19.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.20 Forwarding to a Colleague . . . . . . . . . . . . . . . . 29 3.20.1 Desired Behavior . . . . . . . . . . . . . . . . . . . . . 29 3.20.2 Solution . . . . . . . . . . . . . . . . . . . . . . . . . 29 4. Capability Use Cases . . . . . . . . . . . . . . . . . . . 32 4.1 Web Redirect . . . . . . . . . . . . . . . . . . . . . . . 32 4.2 Voicemail Icon . . . . . . . . . . . . . . . . . . . . . . 32 5. Usage of the Feature Tags . . . . . . . . . . . . . . . . 34 5.1 Traditional Cell Phone . . . . . . . . . . . . . . . . . . 34 5.2 Traditional Work Phone . . . . . . . . . . . . . . . . . . 35 5.3 PC Messenging Application . . . . . . . . . . . . . . . . 35 5.4 Standalone Videophone . . . . . . . . . . . . . . . . . . 35 6. Security Considerations . . . . . . . . . . . . . . . . . 37 7. IANA Considerations . . . . . . . . . . . . . . . . . . . 38 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 39 9. TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Informative References . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 42 Intellectual Property and Copyright Statements . . . . . . 43 Rosenberg & Kyzivat Expires August 16, 2004 [Page 3] Internet-Draft Caller Preferences Uses February 2004 1. Introduction The Session Initiation Protocol (SIP) [1] extension for Callee Capabilities [3] describes mechanisms that allow a UA to register its capabilities in a REGISTER request. A caller can express preferences [2], either explicitly or implicitly, about how that request is to be handled. This is accomplished with the Accept-Contact and Reject-Contact header fields. The caller preferences extension can serve as a useful tool for supporting many applications. However, it generality makes it difficult to correctly and effectively use in any one situation. To remedy that, this document serves as an compendium to the caller preferences extension. This additional information is broken into four sections. First, Section 2 motivates the usage of caller preferences by describing several concrete applications which are enabled by the extension. Section 3 describes a set of detailed use cases for expressing caller preferences. Each use case presents a situation, describes how caller preferences can be used to handle the requirements for the situation, and verifies that the desired behavior occurs by showing the results of the matching operation. These use cases validate that the caller preferences specification is complete, and capable of meeting a specific set of requirements. Since the caller preferences specification pre-dates the SIP change process [4], no requirements work was ever done for it. To some degree, this document "backfills" requirements. However, this is not an academic exercise only, since the use cases described here did result in changes in the caller preferences document as it evolved. These use cases also help implementors figure out how to use it in their own applications. Section 4 discusses applications for the callee capabilities specification. Section 5 discusses the example registrations of the feature tags described in [3]. Proper usage of the caller preferences extension depends on proper interpretation of the semantics of these tags. More detail is provided on the tags, and example registrations are included that show typical usage. Rosenberg & Kyzivat Expires August 16, 2004 [Page 4] Internet-Draft Caller Preferences Uses February 2004 2. Motivations for Caller Preferences At its core, SIP is protocol to facilitate rendezvous of users. The caller and callee need to meet up in order to exchange session information, so that they may communicate. The rendezvous process is complicated by the fact that a user has multiple points of attachment to the network. A user can have a cell phone, a PDA, a work phone, a home phone, and one of several PC-based communications applications. When someone calls a user, to which of these devices is the call routed? Certainly, the call can be routed to all of them at the same time, a process known as parallel forking. However, that is not always the desired behavior. A user will frequently have preferences for their devices, and wish the call to be routed to one of them first. As an example, a user might prefer that their cell phone ring first, and if no one answers, the call rings their work phone next. As an alternative, a user might prefer that their cell phone ring first, and then their home and work phones ring at the same time, and then, if neither answer, the call is forwarded to voicemail. These variations are all referred to as as find-me/follow-me features. SIP supports find-me/follow-me features in many ways. The most basic is through the SIP registration process. Each device at which a user can be contacted registers to the network. This registration associates the device with the canonical name of the user - called the address-of-record (AOR), which is a SIP URI. Each registration can include a preference value, indicating the relative preference for receiving calls at that device, compared to other devices. When someone makes a call to the AOR, proxies compliant to RFC 3261 will try the registered devices in order of preference, unless administrative policy overrides user preferences. Preference values in SIP registrations can only provide basic find-me/follow-me features. To support more complex features, the Call Processing Language (CPL) [5] has been specified. It is an XML script that provides specific call routing instructions. Users can upload these scripts to the network, instructing the servers how calls should be routed. As an example, a CPL script can instruct a proxy to route a call to the work phone during work hours (9am - 5pm) and then to the cell phone after hours, unless the call is from a family member, in which case it always goes to the cell phone. It is important to note that both CPL scripts and preference values in registrations describe operation of a service from the perspective of the called party. That is, they describe how a call made to them should be routed by the network. However, the called party is not the only one with preferences. A caller will also have preferences for Rosenberg & Kyzivat Expires August 16, 2004 [Page 5] Internet-Draft Caller Preferences Uses February 2004 how they want their call to be routed. As an example, a caller will often want to reach a user on their cell phone. In the current telephone network, this is accomplished by requiring a user to have a separate number for each device. This way, when a caller wishes to reach the cell phone, they dial the number for the cell phone. This requires users to maintain lists of potential reach numbers for a user, and then select the appropriate one. A far better approach is for a user to maintain a single address-of-record. When someone wishes to reach them on their cell phone, they call the AOR, but indicate a preference for the call to be routed to the cell phone. A caller may actually have a wide variety of preferences for how a call should be routed. They may prefer to go right to voicemail. They may prefer to never reach voicemail. The may prefer to reach the user on a device which supports video (because a video-conference is desired). They may wish to reach a device that has an attendant who can answer if the user is not there. The SIP caller preferences extension allows a caller to express these preferences for the way in which their calls are handled. These preferences are expressed in terms of properties of the desired device. These properties are name-value pairs that convey some kind of information about a device. One example is the property "mobility" which can have the values "mobile" or "fixed". When a caller wishes to reach a cell phone, they include information in their call setup request (the INVITE method) which indicates that the call should be routed to a device that has the property "mobility" set to "mobile". When devices register to the network, they include their properties - also known as callee capabilities - as part of the registration. In this way, a proxy can match the caller's preferences against the capabilities of the various devices registered to the user, and route the call appropriately. The caller preferences extension can support a wide variety of call routing applications and features. Two particularly important examples are "one-number" and ``direct-to-voicemail''. 2.1 One-Number In today's circuit-switched telephony networks, users have multiple devices, and each device is associated with its own phone number. A user will typically list all of these numbers on a business card - cell phone, work phone, home office phone, and so on. Other users need to store and manage all of these numbers. It is difficult to keep these numbers complete and up-to-date. Worse, when you want to call someone, you need to pick a number to try. Sometimes, you want a specific device (the cell phone), and other times, you just want to reach them wherever they are. In the latter case, a user is forced to Rosenberg & Kyzivat Expires August 16, 2004 [Page 6] Internet-Draft Caller Preferences Uses February 2004 try each number, one at a time. This is inefficient, and difficult to do while driving, for example. As an alternative, a user can have a single address. This is the one and only address they give out to other users on their business cards. If a caller wishes to reach that user on their cell phone, they select that one address, and then access a pull-down menu of device types. This menu would include home phone, work phone, and cell phone. The caller can select cell-phone, and then the call is placed to the cell phone. There is no need to manage or maintain more than one number for the user - a single one will suffice. If, on the other hand, the caller wishes to reach the user wherever they are, they make a call to that one number without a selection of a preferred device. The network will ring all devices at the same time, and therefore reach the user as fast as possible. This one number service makes use of caller preferences. To express a preference for the cell phone, the caller's device would include a header in the SIP INVITE request indicating a desire to reach a device with "mobility" equal to "mobile". 2.2 Direct-to-Voicemail Frequently, a busy executive on the road wants to quickly pass a message to a colleague by voice. As an example, a boss might want to instruct an employee to call a specific customer and resolve a pending issue. In such a case, the user doesn't actually want to talk to the person; they just want to leave them a voice message. Having a phone conversation may require too much time, whereas a voice message can be quick and to the point. The voice message can also serve as a record of exactly what is desired, whereas a fleeting voice conversation can be forgotten or misremembered. In today's circuit-switched telephone networks, there is often no way to go directly to someones voicemail and leave a message. Sometimes, you can dial the main number for the voicemail system, enter in the extension of the desired party, and leave a message by entering a specific prompt. This is time consuming, and requires the caller to know the main voicemail number. Instead, an address book in a cell phone can have an option called "leave voice message", available for each entry in the address book. When this option is selected, a call is made directly to the voicemail for that user, which immediately picks up and prompts for a message. In fact, a rapid greeting is played, so that the caller can go directly to the recording procedure. Rosenberg & Kyzivat Expires August 16, 2004 [Page 7] Internet-Draft Caller Preferences Uses February 2004 This saves time for the caller, making it very easy to quickly leave recorded messages for a large number of people. This feature is possible using the caller preferences extension. When the user selects the "leave voice message" option, the phone sends a SIP INVITE request, and includes a caller preferences header field that indicates a preference for devices whose "msgserver" attribute has a value of "true". This will cause the proxy to route the call directly to a registered voicemail service. Furthermore, the voicemail server will see that the caller asked to go directly to voicemail, and can therefore play an abbreviated greeting explicitly designed for this case. Rosenberg & Kyzivat Expires August 16, 2004 [Page 8] Internet-Draft Caller Preferences Uses February 2004 3. Caller Preference Use Cases Each use case is described as a situation along with a desired behavior. Then, it demonstrates how the various caller preferences headers and the proxy processing logic would result in the appropriate decision being made. 3.1 Routing of INVITE and MESSAGE to different UA 3.1.1 Desired Behavior Address of Record (AOR) Y has two contacts Y1 and Y2. Y1 is a phone, and supports the standard operations INVITE, ACK, OPTIONS, BYE, and so on, while Y2 is a pager and supports only OPTIONS and MESSAGE. Caller X wants to send pages to Y. There is a lot of traffic in the network of both calls and pages, so there is a goal not to unnecessarily fork messages to devices that can't support them. So, ensure that INVITEs of Y are delivered only to Y1, while MESSAGEs to Y are delivered only to Y2. 3.1.2 Solution Y1 will create a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,ACK,OPTIONS,BYE,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip" ;mobility="mobile" Y2 will create a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="OPTIONS,MESSAGE" ;uri-user="" ;uri-domain="example.com" ;+message ;schemes="sip,im" ;mobility="mobile" Rosenberg & Kyzivat Expires August 16, 2004 [Page 9] Internet-Draft Caller Preferences Uses February 2004 When a UAC sends an INVITE, it will arrive at the proxy for example.com. There are no caller preferences in the request. However, per Section 7.2.2 of [2], the proxy will construct an implicit require-flagged Accept-Contact preference that looks like: (& (methods="INVITE")) Applying the matching algorithm of RFC 2533 [6] to this feature set and those registered by Y1 and Y2, the feature set of Y1 alone matches. Because the Accept-Contact predicate has its require flag set, Y2 is discarded and the INVITE is routed to Y1. If the request was MESSAGE, the proxy constructs an implicit require-tagged Accept-Contact preference that looks like: (& (methods="MESSAGE")) which matches the feature set of Y2, but not Y1. Thus, Y1 is discarded, and the request is routed to Y2. 3.2 Single Contact Not Matching Implicit Preferences 3.2.1 Desired Behavior AOR Y has a single contact Y1. Its a phone, and therefore supports the INVITE, BYE, OPTIONS, CANCEL and ACK methods, but not MESSAGE. A caller X sends a MESSAGE request. The desired behavior is that the request is still routed to the solitary contact so that it can generate a 405 response. 3.2.2 Solution The single contact Y1 will generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,ACK,OPTIONS,BYE,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip" ;mobility="fixed" ;class="personal" Rosenberg & Kyzivat Expires August 16, 2004 [Page 10] Internet-Draft Caller Preferences Uses February 2004 X sends a MESSAGE request. There are no explicit caller preferences. This results in an implicit require-flagged Accept-Contact preference: (& (methods="MESSAGE")) Since Y1 doesn't match and the Accept-Contact predicate is require-flagged, it is discarded. However, according to the specifications, if there are no matching targets, the original target set is used, with its original q-values. Thus, the request is sent to the one original target, Y1, as desired. Y1 then responds with a 405. 3.3 Package-Based Routing 3.3.1 Desired Behavior AOR Y has a number of contacts, Y1, Y2, ..., Yn that can each support normal calls - INVITE, ACK, BYE, etc., and can also support SUBSCRIBE for the "dialog" event package [7]. Y also has another contact Yp that is a presence agent (PA) [8] - it can accept SUBSCRIBE requests for the "presence" event package. The goal is for subscribe requests for presence to be routed to Yp while invites and subscribes for the dialog package are forked to Y1...Yn. 3.3.2 Solution Y1..Yn will generate REGISTER requests which look like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL,SUBSCRIBE" ;events="dialog" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip" ;mobility="fixed" ;class="personal" and Yp will generate a REGISTER request which looks like, in part: Rosenberg & Kyzivat Expires August 16, 2004 [Page 11] Internet-Draft Caller Preferences Uses February 2004 REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="SUBSCRIBE" ;events="presence" ;uri-user="" ;uri-domain="example.com" ;schemes="sip,pres" ;mobility="fixed" ;class="business" A SUBSCRIBE request for presence will arrive at the proxy for example.com. Since there are no explicit preferences, it constructs an implicit require-tagged Accept-Contact preference from the request: (& (methods="SUBSCRIBE") (events="presence")) This feature set only matches the one registered by Yp. Because the require flag is set, the contacts which do not match are removed from the target set. Therefore, Y1..Yn are eliminated. The request is sent to the remaining contact, Yp, representing the PA. An INVITE request without explicit preferences results in an implicit require-flagged Accept-Contact preference: (& (methods="INVITE")) The implicit Accept-Contact feature set matches Y1..Yn, but not Yp. The score for Y1..Yn against this predicate is 1.0. As a result, the caller preference Qa for each contact is 1.0. The registrations did not contain q-values, so the default q-value of 1.0 is applied to each Contact URI. Since the caller and callee preferences are the same, and all equal to 1.0, there is no reordering of contacts. The result is that the proxy will consider Y1..Yn each as equally good targets for the request, and possibly fork the request to each. A SUBSCRIBE request for the dialog event package without explicit preferences will result in an implicit require-flagged Accept-Contact preference: (& (methods="SUBSCRIBE") (events="dialog")) This only matches Y1..Yn, so Yp is discarded, and the request is routed to the remaining contacts just as the INVITE was. Rosenberg & Kyzivat Expires August 16, 2004 [Page 12] Internet-Draft Caller Preferences Uses February 2004 3.4 Package Routing II 3.4.1 Desired Behavior This case is nearly identical to that of Section Section 3.3. However, Y1..Yn omit the "events" feature tag from their registration. Yp registers as in Section Section 3.3. A SUBSCRIBE for the presence event package should still preferentially route to Yp. 3.4.2 Solution The registration from Y1..Yn will look like: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL,SUBSCRIBE" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip" ;mobility="fixed" ;class="personal" When the caller sends a SUBSCRIBE for the presence event package (without explicit preferences), the proxy computes an implicit preference: (& (methods="SUBSCRIBE") (events="presence")) This predicate matches Y1..Yn and Yp. However, the score for Y1..Yn against this predicate is 0.5, and the score of Yp is 1.0. The result is a caller preference Qa of 0.5 for Y1..Yn, and a caller preference Qa of 1.0 for Yp. Since the callee provided no q-values, the proxy will assume a default of 1.0. Thus, all contacts are in the same equivalence class. They are then sorted by Qa, so that Yp is first, followed by Y1 through Yn. It will therefore route the request first to Yp, and if that should fail, to Y1..Yn. 3.5 Audio/Video vs. Audio Only 3.5.1 Desired Behavior X sends an invitation to Y to initiate an audio/video call, including both m=audio and m=video lines in the SDP. AOR Y has two contacts, Y1 and Y2. Y1 represents a normal audio phone, where Y prefers to Rosenberg & Kyzivat Expires August 16, 2004 [Page 13] Internet-Draft Caller Preferences Uses February 2004 receive their calls. It will answer an audio/video call, refusing the video. Y2 represents an audio/video phone that should only used when needed. The caller really wants the called answered by a device that supports video, but will take an audio-only call as a second choice. 3.5.2 Solution Y1 will generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;q=1.0 ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip,tel" ;mobility="fixed" ;class="business" Y2 will generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;q=0.6 ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;video ;schemes="sip,tel" ;mobility="fixed" ;class="business" Note the different q-values, allowing Y2 to be selected as a device of "last resort". To have the call is preferentially routed to a device that supports video, the caller X sends an INVITE that looks like, in part: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: * ;methods="INVITE" ;video Rosenberg & Kyzivat Expires August 16, 2004 [Page 14] Internet-Draft Caller Preferences Uses February 2004 The proxy will convert this to a feature set. This feature set matches Y2 and Y1. However, the score for Y2 is 1.0, and 0.5 for Y1. The two contacts are then ordered by q-value, and broken into equivalence classes. There are two equivalence classes, each with one contact. As a result, the caller preference values have no impact on the ordering. The call will first try the higher priority Y1, which will answer the call and reject the video stream. Thus, the desired behavior is not achieved. The desired behavior could be achieved by adding the "explicit" and "require" tags to the Accept-Contact header field in the INVITE, as is done in Section 3.6. However, doing so may result in calls failing when they could occur, but without video. As discussed in [2], both the "require" and "explicit" tags are generally used only when the request cannot be serviced in any way unless the preferences are met. That is not the case here. OPEN ISSUE: This is a use case that used to work, but no longer works because of the change in the way q-values are used. I think the loss of support for this use case is acceptable. I also believe it is worthwhile to keep this case in the use cases spec to illustrate that not everything is possible. 3.6 Forcing Audio/Video 3.6.1 Desired Behavior This case is similar to that of Section 3.5. However, X requires an audio/video call, and would like the call to fail if this is not possible, rather than succeeding with audio only. 3.6.2 Solution The solution is similar to that of Section 3.5, however the Accept-Contact header field now includes the explicit and require tags, guaranteeing that the call is never established to any UA that had not explicitly indicated support for video: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;video;require;explicit This arrives at the example.com proxy. This explicit feature set matches the feature set for Y2 and Y1. However, the match for Y1 did not have a score of 1. Since the explicit and require tags are present, the contact is discarded. That leaves Y2 only. The call will therefore get routed to the videophone, and if the user is not there, Rosenberg & Kyzivat Expires August 16, 2004 [Page 15] Internet-Draft Caller Preferences Uses February 2004 the audio phone will never ring. Because both the "require" and "explicit" flags are present, a contact will also be discarded if it didn't say anything about support for video. Thus, a UA that can do video, but neglected to indicate it, would not be reached in this case. This is why it is important for a UA to indicate all of its capabilities. Note that this is only true for a contact that indicated other capabilities, just not video. Contacts which don't indicate any capabilities are "immune" from caller preferences filtering, and would not be discarded. 3.7 Third Party Call Control - Forcing Media 3.7.1 Desired Behavior Z is a third party call control controller [9] trying to establish an audio/video call from X to Y. X has contacts X1 and X2, and Y has contacts Y1 and Y2. X1 and X2 have capabilities identical to Y1 and Y2, respectively. Z needs to send an offerless invite to X and use the offer proposed by X to send an invite to Y. When sending the offerless invite to X the 3pcc controller must ensure that an audio/ video contact (X2) is chosen over an audio only contact (X1). 3.7.2 Solution X1 will generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:X@example.com Contact: ;q=1.0 ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip,tel" ;mobility="fixed" ;class="business" X2 will generate a registration which looks like, in part: Rosenberg & Kyzivat Expires August 16, 2004 [Page 16] Internet-Draft Caller Preferences Uses February 2004 REGISTER sip:example.com SIP/2.0 To: sip:X@example.com Contact: ;q=0.6 ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;video ;schemes="sip,tel" ;mobility="fixed" ;class="business" Z would include, in its INVITE, an Accept-Contact header field: INVITE sip:X@example.com SIP/2.0 Accept-Contact: *;audio;video;require;explicit This caller preference matches both X1 and X2. However, it matches X1 with a score of .5 and X2 with a score of 1. Because of the require and explicit tags, X1 is discarded despite X's preference for it. Thus, the call is routed to X2. The same caveats apply here as do in Section 3.6. Generally, it is not advisable to mandate support for features (such as video), which are not strictly neccesary for the request to proceed. 3.8 Maximizing Media Overlaps 3.8.1 Desired Behavior AOR Y has two contacts, Y1 that is a regular audio phone, and Y2 that is a PC capable of supporting both audio and session oriented IM [10]. X is a PC with capability to support audio, video and session oriented IM. X calls Y for the purpose of establishing a voice call. However, X wishes to connect to the device which has the maximal overlap with its media capabilities, in order to maximize the functionality available to the caller. 3.8.2 Solution Y1 will generate a registration which looks like, in part: Rosenberg & Kyzivat Expires August 16, 2004 [Page 17] Internet-Draft Caller Preferences Uses February 2004 REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL" ;uri-user="" ;uri-domain="example.com" ;audio ;schemes="sip,tel" ;mobility="fixed" ;class="business" Y2 will generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: ;methods="INVITE,BYE,OPTIONS,ACK,CANCEL,MESSAGE" ;uri-user="" ;uri-domain="example.com" ;audio ;+message ;schemes="sip,tel" ;mobility="fixed" ;class="business" The solution requires the caller to support caller preferences. They would include, in their INVITE, an Accept-Contact header field that lists all the media types they support. In this case: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;audio;video;+message Both Y1 and Y2 match the predicate. Y1 matches with a score of 0.33, and Y2 matches with a score of 0.66. Since there is only one Accept-Contact predicate, the Qa for each contact is equal to the score. The registered contacts are then sorted by q-value, and broken into equivalence classes. There is a single equivalence class with q-value of 1.0. The two contacts in that class are then re-ordered based on the values of Qa. Y2 has a higher Qa, so it is used first, followed by Y1. The result is that the call is routed to the device with the maximum overlap in media capabilities, as desired. EDITORS NOTE: This is a case that didn't work well before caller prefs -09, but works very well now - as long as the registered contacts have the same q-value. Rosenberg & Kyzivat Expires August 16, 2004 [Page 18] Internet-Draft Caller Preferences Uses February 2004 3.9 Multilingual Lines 3.9.1 Desired Behavior AOR Y represents a shared line in an office. Several employees in the office have phones registered for Y. Some of the employees speak only English, some speak Spanish fluently and have some limited capability for English, and some speak both English and Spanish fluently. Calls from callers that speak only English should be parallel forked to all office workers that speak fluent English. If the call isn't picked up, then the phones of workers that speak English marginally should be rung. Calls from callers that speak only Spanish should be forked only to workers that speak Spanish. 3.9.2 Solution A user at phone Y1 that speaks English only would generate a REGISTER which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y1@pc.example.com;languages="en" A user at a phone Y2 that speak Spanish and a little bit of English would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y2-es@pc2.example.com;languages="es" Contact: ;languages="en";q=0.2 Y2 has registered two contacts. Both of them route to the same device (pc2.example.com), but they differ in their language support and relative q-values. Multiple contacts are needed whenever a UA wishes to express differing preferences for being reached for different feature collections. A user at phone Y3 that speaks English and Spanish fluently would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y3@pc3.example.com;languages="es,en" Notice that only a single contact is needed because the same q-value Rosenberg & Kyzivat Expires August 16, 2004 [Page 19] Internet-Draft Caller Preferences Uses February 2004 is applied across all feature collections. For the language based routing to occur, the caller must indicate its language preferences explicitly: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;languages="en";require The predicate derived from this looks like: (& (languages="en")) This matches all Y1 phones, the second contact registered by Y2 phones, and Y3 phones, all with a score of 1.0. The first contact registered by Y2 does not match, and because of the "require" flag, is discarded. The remaining contacts are sorted by q-value, and divided into equivalence classes. There are two equivalence classes. The first contains Y1 and Y3 with a q-value of 1.0, and the second contains Y2-en with a q-value of 0.2. The contacts in the first class are ordered by Qa. However, since all contacts have the same value of Qa (1.0), there is no change in ordering. Thus, Y1 and Y3 are tried first, followed by Y2-en. This is the desired behavior. A caller that speaks Spanish only would specify their preference thusly: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;languages="es";require This matches the first contact of Y2 phones, and Y3 phones, all with a score of 1.0. The English contact of Y2, Y2-en, doesn't match, and is discarded because of the "require" flag. The remaining contacts are sorted by q-values (Y3, Y2-es), and broken into a single equivalence class containing both contacts. Since the Qa for both contacts is the same - 1.0 - there is no reordering. The result is that the call is routed to either Y3 or Y2-es. 3.10 I Hate Voicemail! 3.10.1 Desired Behavior AOR Y has two contacts, a phone Y1 and a voicemail service Y2. X wishes to call Y and talk in person. X does not want to be sent to voicemail under any circumstance. Rosenberg & Kyzivat Expires August 16, 2004 [Page 20] Internet-Draft Caller Preferences Uses February 2004 3.10.2 Solution The phone would register with a Contact that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y1@pc.example.com ;audio ;mobility="fixed" and the voicemail server would register with a Contact that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y2@pc.example.com ;msgserver ;automata ;attendant ;audio ;q=0.2 The voicemail server registers with a lower q-value so that it is used only after the phone itself is rung. Note that the voicemail server need not actually register. There can be a configured contact and feature set defined for it instead. A caller that wishes to avoid voicemail can include an explicit preference to avoid it. It would do this with the Reject-Contact header field: INVITE sip:Y@example.com SIP/2.0 Reject-Contact: *;msgserver Since this feature set contains a feature tag that is not contained in the registration for Y1, the feature set is discarded when examining Y1. However, the registration for Y2 contains all feature tags listed in the feature set, and so the rule is considered. There is a match, and therefore, Y2 is discarded. The result is that the user is never routed to voicemail. 3.11 I Hate People! Rosenberg & Kyzivat Expires August 16, 2004 [Page 21] Internet-Draft Caller Preferences Uses February 2004 3.11.1 Desired Behavior The situation is similar to Section 3.10, except the caller wishes to only leave a message, not actually speak to the person. 3.11.2 Solution The caller would send an INVITE which looks like, in part: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;msgserver;require;explicit This caller preference matches both Y1 and Y2. Y1 matches, but with a score of zero. Y2 matches with a score of 1. Since both the require and explicit flags are set, Y1 is discarded. Therefore, the call is routed to Y2, the voicemail server, as desired. If these preferences are used with a user that doesn't have voicemail at all, the call will fail completely, rather than connecting to the user. 3.12 Prefer Voicemail 3.12.1 Desired Behavior The situation is similar to that of Section 3.10. However, the caller prefers to leave a message. If voicemail is not available, they are willing to talk to a person. 3.12.2 Solution OPEN ISSUE: This cannot be done with caller prefs -09, as it would require a re-ordering of the callee contacts, which is not done. Is there another way? Is it OK to set a callee contact to q=0.0? 3.13 Routing to an Executive 3.13.1 Desired Behavior Y is the AOR of an executive. It has three contacts. Y1 is the phone on the executive's desk. Y2 is the phone on the desk of the executive's assistant. Y3 is the address of an auto-attendant system that can answer general questions, route calls to other parties, etc. By default, calls to Y should be directed to Y2, and if that fails, Rosenberg & Kyzivat Expires August 16, 2004 [Page 22] Internet-Draft Caller Preferences Uses February 2004 to Y3. If Y3 doesn't answer then Y1 should ring. 3.13.2 Solution This is primarily a called party feature, and is best accomplished with a CPL script [5]. However, it can be accomplished with caller preferences alone by properly setting the q-values across the three devices. Assuming this coordination is possible, here are the settings that would be made: Y1 would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y1@pc.example.com;q=0.1 Y2 would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y2@pc2.example.com;attendant;q=1.0 Y3 would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y3@pc3.example.com;attendant;automata;q=0.5 Note that, in reality, the automated attendant would probably not use REGISTER. Since the attendant would be used for every employee in the company, a static contact would probably be added administratively for each user in the enterprise. However, the information in that static contact would be identical to the information in the registration above. When X makes a call to the executive, Y, and expresses no preference, the proxy computes an implicit preference to support INVITE. All three contacts match such a preference, even though they have not indicated explicit support for INVITE. Thus, no contacts are discarded. Since the contacts each have a different q-value, the caller preferences do not cause any reordering. The result is that the call is first routed to Y2, then Y3, then Y1, all as a result of the proper setting of the q-values. Rosenberg & Kyzivat Expires August 16, 2004 [Page 23] Internet-Draft Caller Preferences Uses February 2004 3.14 Speak to the Executive 3.14.1 Desired Behavior This case is similar to that of Section 3.13, but this time the caller, X, has a preference. X calls Y, but wants to speak directly to the executive. X doesn't want the call to ring either the assistant or the auto attendant (automata). 3.14.2 Solution X's INVITE would look like, in part: INVITE sip:Y@example.com SIP/2.0 Reject-Contact: *;attendant Reject-Contact: *;automata Note that the caller uses two separate Reject-Contact header field values, rather than a single one with two separate feature parameters. The distinction is important. If X had use a single value with two parameters, a matching UA would need to declare that it was BOTH an attendant and an automata. If it only declared that it was one of these, based on the matching rules in the caller preferences specification, it would not be rejected. The above request would result in the elimination of both Y2 and Y3 as contacts. The call would then be routed to Y1, as desired. This case indicates why a CPL script, or some other programmed version of the feature, is preferrable. With caller preferences, a caller can override the desired ring sequence, and disturb the executive without any kind of authorization. A proper version of this service would simply not permit caller preferences to force the call to go directly to the executive. OPEN ISSUE: Should we discard this use case as a result? 3.15 Mobile Phone Only 3.15.1 Desired Behavior The situation is similar to that in Section 3.13. However, the executive also has a mobile phone which they have registered. Caller X knows that the owner of Y is traveling, and that an assistant is covering the office phone. X wants to call Y and ring only the mobile phone. Rosenberg & Kyzivat Expires August 16, 2004 [Page 24] Internet-Draft Caller Preferences Uses February 2004 3.15.2 Solution The mobile phone would generate a registration which looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y4@mobile.example.com;mobility="mobile";q=0.5 The caller would express their preference by generating an INVITE which looks like, in part: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;mobility="mobile";require;explicit All four contacts match. However, Y1 through Y3 match with a score of zero. Y4 matches with a score of 1. Because of the require and explicit tags, Y1 through Y3 are discarded, and only Y4 is used, as desired. 3.16 Simultaneous Languages 3.16.1 Desired Behavior AOR Y is as in Section 3.9. Caller X, fluent in both English and Spanish, has discovered that company's Spanish language documentation is inconsistent with the English language documentation, and wants to discuss the differences between the two. So X wants to speak with one of the workers that is fluent in both English and Spanish. 3.16.2 Solution The caller would generate an INVITE which looks like, in part: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;language="en";require Accept-Contact: *;language="es";require This will require a Contact URI to match both constraints. That means it needs to support English and Spanish. This will achieve the desired property. Note that there are two separate Accept-Contact header fields. If the caller had instead used this INVITE: Rosenberg & Kyzivat Expires August 16, 2004 [Page 25] Internet-Draft Caller Preferences Uses February 2004 INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;language="en,es";require It would have connected them to a UA that speaks either English or Spanish, which is not what is desired here. 3.17 UA Routing 3.17.1 Desired Behavior AOR Y has contacts Y1 and Y2. The addresses Y1 and Y2 are behind a firewall and are not addressable by all callers. Caller X makes a call to Y and is connected to Y1. The call fails for some reason, and X wants to reestablish it, reaching only Y1. 3.17.2 Solution There is currently no generally workable solution to this problem. The best solution that exists does make use of caller preferences. Lets say that the Contact URI for Y1 was sip:Y1@host.example.com. The caller would generate an INVITE which looks like, in part: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: * ;require ;explicit ;uri-user="" ;uri-domain="host.example.com" When this request arrives at the proxy for example.com, it attempts to apply the caller preferences. Following the guidelines in the caller preferences extension, Y1 would have included a uri-user and uri-domain feature tag in its registration: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y1@host.example.com;uri-user="" ;uri-domain="host.example.com" as would have Y2: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:Y2@pc.example.com;uri-user="" ;uri-domain="pc.example.com" Rosenberg & Kyzivat Expires August 16, 2004 [Page 26] Internet-Draft Caller Preferences Uses February 2004 The proxy then applies the caller preferences. Only Y1 is a match. So, Y2 is discarded, and the request is routed to Y1 as desired. The difficulty is that this solution won't always work. In a multi-proxy scenario, it is possible that the routing logic changes, and therefore the request is never even routed to the proxy where Y1 has registered. 3.18 The Number you Have Called.. 3.18.1 Desired Behavior Consider once more the case of the executive, where the caller wishes to reach only their mobile phone (Section 3.15). However, there is a twist. The callee Y has moved to new address YY, and all the configuration described for the callee now applies to YY. The old address Y remains with a pair of statically assigned contacts. One contact is YY. The other is M referencing an automaton that generates a voice message reporting that the number has been changed. The caller is unaware of the move and calls Y, requesting to reach the mobile phone in exactly the same way they did in Section 3.15. The call should connect to the mobile. 3.18.2 Solution There would be four registrations against YY: YY1, the executive, would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:YY@example.com Contact: sip:YY1@pc.example.com;q=0.1 YY2, the attendant, would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:YY@example.com Contact: sip:YY2@pc2.example.com;attendant;q=1.0 YY3, the answering service, would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 Rosenberg & Kyzivat Expires August 16, 2004 [Page 27] Internet-Draft Caller Preferences Uses February 2004 To: sip:YY@example.com Contact: sip:YY3@pc3.example.com;attendant;automata;q=0.5 YY4, the mobile, would generate a REGISTER that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:YY@example.com Contact: sip:YY4@mobile.example.com;mobility="mobile";q=0.5 Athough it would be configured administratively, there are two registered contacts for Y. The first is for the forwarding: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:YY@example.com;q=1.0 and the second for the automated answering service: REGISTER sip:example.com SIP/2.0 To: sip:Y@example.com Contact: sip:machine@example.com;automata;q=0.5 The caller, not knowing that Y has moved, calls Y and asks for their mobile phone: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;mobility="mobile";require;explicit This reaches the example.com proxy, which finds two registrations. Only one of these is associated with feature parameters (the automata). The other has no feature parameters, and is therefore immune from caller preferences processing. The caller preferences are applied to the the automata's contact. The feature sets match, but have a score of zero. Since the require and explicit tags are present, the contact for the automata is dropped. The other contact, YY@example.com, is then added back in as the sole contact. The proxy therefore sends the call to sip:YY@example.com. There, there are four registrations, all of which are associated with feature parameters. The caller preferences are applied. Only YY4 matches explicitly, however. Because of the presence of the require and explicit flags, all other contacts are dropped. As such, the call is forwarded to YY4, and the mobile phone rings. Rosenberg & Kyzivat Expires August 16, 2004 [Page 28] Internet-Draft Caller Preferences Uses February 2004 3.19 The Number you Have Called, Take Two 3.19.1 Desired Behavior This use case is nearly identical to that of Section 3.18. However, this time, the caller wishes to contact the personal phone of Y. They don't feel strongly about it, and will accept other devices. 3.19.2 Solution The INVITE generated by the caller in this case will look like: INVITE sip:Y@example.com SIP/2.0 Accept-Contact: *;class="personal" This reaches the example.com proxy. Once more, the first registration (which forwards to the address-of-record for YY) is unaffected by the caller preferences computation. The other contact, for the automata, is a match, but its score is zero. Its caller preference Qa equals zero. The other contact is added back in with a Qa of 1.0. The contacts are sorted based on q-value, resulting in YY (q=1.0) followed by machine (q=0.5). These are broken into equivalence classes. There are two classes, one for each contact. As a result, the caller's preferences have no impact on the ordering, and the call is routed to YY. When processing the request for YY@example.com, all four contacts match. However, the score for all of them is zero (none are the personal phone). As such, the contacts are ordered based on q-value. Each contact has a different q-value, so no reordering based on caller preference is possible (not that the caller preference would cause a reordering - all contacts have a Qa of 0.0). Thus, the highest q-value contact is tried, which is the executive assistant. 3.20 Forwarding to a Colleague 3.20.1 Desired Behavior Alice wants to forward her phone to Bob, but doesn't want folks calling her to get Bob's voicemail if he doesn't answer. She wants her callers to get her voicemail. 3.20.2 Solution Alice would create three registrations. The first, Y1, represents Alice's phone. The second is Bob's AOR. The third is a voicemail server. The three contacts have decreasing q-values. The registration Rosenberg & Kyzivat Expires August 16, 2004 [Page 29] Internet-Draft Caller Preferences Uses February 2004 for Bob's AOR contains an embedded Reject-Contact header field, which rejects message servers. REGISTER sip:example.com To: Contact: ;q=1.0 REGISTER sip:example.com To: Contact: ;q=0.3 REGISTER sip:example.com To: Contact: ;msgserver; ;automata ;attendant ;q=0.1 Meanwhile, Bob is registered as follows: REGISTER sip:example.com To: Contact: ;q=0.8 REGISTER sip:example.com To: Contact: ;msgserver ;automata ;attendant ;q=0.2 Carol calls Alice, and doesn't include any caller preference parameters. As such, the example.com proxy constructs an implicit preference for INVITE. This preference matches all three registered contacts, with a score of zero. Because each contact has a different q-value, there is no reordering of contacts. So, the proxy tries the highest q-value Contact, Alice's desk phone (Y1). The proxy cancels after a few seconds (no answer). The proxy then tries the next Contact, which is Bob's AOR. When constructing the request for this Contact, the proxy includes the embedded Reject-Contact header field Rosenberg & Kyzivat Expires August 16, 2004 [Page 30] Internet-Draft Caller Preferences Uses February 2004 in the INVITE. This INVITE undergoes caller preferences processing based on Bob's registered Contacts. Bob has two registered Contacts. The second is a message server, and it matches the Reject-Contact in the INVITE. Thus, this contact is discarded. The other remaining Contact, Bob's phone, is tried. Bob is not around, and so his phone rings for a while. Upon timeout, the proxy determines it is unable to reach Bob's AOR. So, the proxy handling Alice tries the final remaining contact, which is Alice's message server. Rosenberg & Kyzivat Expires August 16, 2004 [Page 31] Internet-Draft Caller Preferences Uses February 2004 4. Capability Use Cases The callee capabilities spec [3] allows the Contact header field in OPTIONS responses and dialog initiating messages to contain capabilities of the UA. These capabilities can be very useful for developing new applications. In the subsections below, several usages are outlined. 4.1 Web Redirect A caller sends an INVITE to the called party. However, the called party is not present. The proxy server representing the called party would like to redirect the caller to a web page, where they can find out more information on how to reach the called party. However, the proxy needs to know whether or not the caller supports redirects to web pages. If it doesn't, the proxy would connect the user to an IVR, which would execute an answering machine application. The proxy could make such a determination if the caller included the "schemes" feature tag in the Contact header field of its INVITE: INVITE sip:callee@example.com SIP/2.0 Contact: sip:host22.example.com;schemes="http,sip,sips,tel" This tells the proxy that the UAC can be redirected to an http URI. The INVITE from a normal "black phone" which lacked this capability would look like: INVITE sip:callee@example.com SIP/2.0 Contact: sip:host22.example.com;schemes="sip,sips,tel" which indicates that it needs to be connected to the IVR. 4.2 Voicemail Icon On the circuit network, when a user makes a call, and an answering machine picks up, the caller usually requires several seconds to make the determination that they are speaking to an answering machine. It would be helpful if a phone could display an icon immediately on call completion that indicated that an answering machine was reached. This indication can be provided by the "msgserver" feature parameter. When the answering machine picks up, its 200 OK looks like, in part: SIP/2.0 200 OK Rosenberg & Kyzivat Expires August 16, 2004 [Page 32] Internet-Draft Caller Preferences Uses February 2004 Contact: sip:server33.example.com;msgserver;automata;attendant This tells the caller that its an answering machine. Rosenberg & Kyzivat Expires August 16, 2004 [Page 33] Internet-Draft Caller Preferences Uses February 2004 5. Usage of the Feature Tags The caller preferences extension briefly enumerates a list of media feature tags which can be registered by a device, and included in the Accept-Contact and Reject-Contact header fields in a request. Proper operation of caller preferences depends strongly on consistent interpretation of these feature tags by the caller and the callee. In this section, we provide some guidelines on the usage of these feature tags. Generally speaking, the more information a device provides when it registers, the more effective the caller preferences extension is. This is why the callee capabilities extension recommends that a device register as much information as it can. This point cannot be understated. OPEN ISSUE: Should we advise devices to register things they can't do? As an example, if a phone doesn't support video, it would include a "video=FALSE" feature parameter in its registration to indicate that. This provides more information, and would improve the operation of caller preferences, but can seriously bloat registrations. It also seems odd to have to say what you can't do. The subsections below show example registrations from typical devices. 5.1 Traditional Cell Phone A VoIP cell phone capable of making voice calls would generate a registration that looks like, in part: REGISTER sip:example.com SIP/2.0 To: sip:user@example.com Contact: sip:cell-phone@example.com ;audio ;class="business" ;duplex="full" ;sip-extensions="100rel,path" ;mobility="mobile" ;methods="INVITE,BYE,OPTIONS,CANCEL,ACK" ;schemes="sip,sips,tel" ;uri-user="" ;uri-domain="example.com" Rosenberg & Kyzivat Expires August 16, 2004 [Page 34] Internet-Draft Caller Preferences Uses February 2004 5.2 Traditional Work Phone A traditional landline IP PBX phone would generate a registration that looks like: REGISTER sip:example.com SIP/2.0 To: sip:user@example.com Contact: sip:ippbx-phone@example.com ;audio ;class="business" ;duplex="full" ;events="dialog" ;sip-extensions="100rel,privacy" ;mobility="fixed" ;methods="INVITE,BYE,OPTIONS,CANCEL,ACK,SUBSCRIBE" ;schemes="sip,sips,tel" ;uri-user="" ;uri-domain="example.com" This device also supports the dialog event package and several SIP extensiosn that would be typical in an IP PBX phone. 5.3 PC Messenging Application A PC messenger client, capable of just doing presence and IM (no voice) would generate a registration that looks like: REGISTER sip:example.com SIP/2.0 To: sip:user@example.com Contact: sip:pc-msgr@example.com ;class="personal" ;mobility="fixed" ;methods="OPTIONS,MESSAGE,NOTIFY" ;schemes="sip,sips,im,pres" ;uri-user="" ;uri-domain="example.com" 5.4 Standalone Videophone A standalone IP videophone, capable of audio and video would generate a registration that looks like, in part Rosenberg & Kyzivat Expires August 16, 2004 [Page 35] Internet-Draft Caller Preferences Uses February 2004 REGISTER sip:example.com SIP/2.0 To: sip:user@example.com Contact: sip:vp@example.com ;audio ;video ;class="business" ;duplex="full" ;mobility="fixed" ;methods="INVITE,BYE,OPTIONS,CANCEL,ACK" ;schemes="sip,sips,tel" ;uri-user="" ;uri-domain="example.com" Rosenberg & Kyzivat Expires August 16, 2004 [Page 36] Internet-Draft Caller Preferences Uses February 2004 6. Security Considerations There are no security considerations associated with this specification. Rosenberg & Kyzivat Expires August 16, 2004 [Page 37] Internet-Draft Caller Preferences Uses February 2004 7. IANA Considerations There are no IANA considerations associated with this specification. Rosenberg & Kyzivat Expires August 16, 2004 [Page 38] Internet-Draft Caller Preferences Uses February 2004 8. Acknowledgements The authors would like to thank Rohan Mahy for his input in this specification. Rosenberg & Kyzivat Expires August 16, 2004 [Page 39] Internet-Draft Caller Preferences Uses February 2004 9. TODO o Add a section showing an example implementation of the matching algorithm in caller preferences [[OPEN ISSUE: Do we want this?]]. o Provide additional explanations in each routing use case on why require and/or explicit tags were used. o Show examples using the message server, automata, and attendant tags. Rosenberg & Kyzivat Expires August 16, 2004 [Page 40] Internet-Draft Caller Preferences Uses February 2004 Informative References [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [2] Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Caller Preferences for the Session Initiation Protocol (SIP)", draft-ietf-sip-callerprefs-10 (work in progress), October 2003. [3] Rosenberg, J., "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", draft-ietf-sip-callee-caps-03 (work in progress), January 2004. [4] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J. and B. Rosen, "Change Process for the Session Initiation Protocol (SIP)", BCP 67, RFC 3427, December 2002. [5] Lennox, J. and H. Schulzrinne, "Call Processing Language Framework and Requirements", RFC 2824, May 2000. [6] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC 2533, March 1999. [7] Rosenberg, J. and H. Schulzrinne, "An INVITE Inititiated Dialog Event Package for the Session Initiation Protocol (SIP)", draft-ietf-sipping-dialog-package-03 (work in progress), October 2003. [8] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work in progress), January 2003. [9] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo, "Best Current Practices for Third Party Call Control in the Session Initiation Protocol", draft-ietf-sipping-3pcc-06 (work in progress), January 2004. [10] Campbell, B., "Instant Message Sessions in SIMPLE", draft-ietf-simple-message-sessions-03 (work in progress), January 2004. Rosenberg & Kyzivat Expires August 16, 2004 [Page 41] Internet-Draft Caller Preferences Uses February 2004 Authors' Addresses Jonathan Rosenberg dynamicsoft 600 Lanidex Plaza Parsippany, NJ 07054 US Phone: +1 973 952-5000 EMail: jdrosen@dynamicsoft.com URI: http://www.jdrosen.net Paul Kyzivat Cisco Systems Mail Stop LWL3/12/2 900 Chelmsford St. Lowell, MA 01851 US EMail: pkzivat@cisco.com Rosenberg & Kyzivat Expires August 16, 2004 [Page 42] Internet-Draft Caller Preferences Uses February 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. 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