BLISS A. Johnston, Ed.
Internet-Draft Avaya
Intended status: Standards Track M. Soroushnejad
Expires: January 13, 2011 V. Venkataramanan
Sylantro Systems Corp
July 12, 2010
Shared Appearances of a Session Initiation Protocol (SIP) Address of
Record (AOR)
draft-ietf-bliss-shared-appearances-06
Abstract
This document describes the requirements and implementation of a
group telephony feature commonly known as Bridged Line Appearance
(BLA) or Multiple Line Appearance (MLA), or Shared Call/Line
Appearance (SCA). When implemented using the Session Initiation
Protocol (SIP), it is referred to as shared appearances of an Address
of Record (AOR) since SIP does not have the concept of lines. This
feature is commonly offered in IP Centrex services and IP-PBX
offerings and is likely to be implemented on SIP IP telephones and
SIP feature servers used in a business environment. This feature
allows several user agents (UAs) to share a common AOR, learn about
calls placed and received by other UAs in the group, and pick up or
join calls within the group. This document discusses use cases,
lists requirements and defines extensions to implement this feature.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 13, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Conventions used in this document . . . . . . . . . . . . . . 6
3. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Executive/Assistant Arrangement . . . . . . . . . . . . . 6
3.2. Call Group . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Single Line Extension . . . . . . . . . . . . . . . . . . 7
3.4. Changing UAs . . . . . . . . . . . . . . . . . . . . . . 7
4. Requirements and Implementation . . . . . . . . . . . . . . . 7
4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Implementation . . . . . . . . . . . . . . . . . . . . . 9
5. Normative Description . . . . . . . . . . . . . . . . . . . . 11
5.1. Elements . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Shared Appearance Dialog Package Extensions . . . . . . . 12
5.2.1. The <appearance> element . . . . . . . . . . . . . . . 12
5.2.2. The <exclusive> element . . . . . . . . . . . . . . . 12
5.2.3. The <joined-dialog> element . . . . . . . . . . . . . 13
5.2.4. The <replaced-dialog> element . . . . . . . . . . . . 13
5.3. Shared Appearance User Agents . . . . . . . . . . . . . . 13
5.4. Appearance Agent . . . . . . . . . . . . . . . . . . . . 16
6. XML Schema Definition . . . . . . . . . . . . . . . . . . . . 18
7. User Interface Considerations . . . . . . . . . . . . . . . . 20
7.1. Appearance Number Rendering . . . . . . . . . . . . . . . 20
7.1.1. Single Appearance UAs . . . . . . . . . . . . . . . . 20
7.1.2. Dual Appearance UAs . . . . . . . . . . . . . . . . . 20
7.1.3. Shared Appearance UAs with Fixed Appearance Number . . 20
7.1.4. Shared Appearance UAs with Variable Appearance
Number . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2. Call State Rendering . . . . . . . . . . . . . . . . . . 21
8. Interop with non-Shared Appearance UAs . . . . . . . . . . . . 22
8.1. Appearance Assignment . . . . . . . . . . . . . . . . . . 22
8.2. Appearance Release . . . . . . . . . . . . . . . . . . . 22
8.3. UAs Supporting Dialog Events but Not Shared Appearance . 23
9. Provisioning Considerations . . . . . . . . . . . . . . . . . 23
10. Example Message Flows . . . . . . . . . . . . . . . . . . . . 23
10.1. Registration and Subscription . . . . . . . . . . . . . . 24
10.2. Appearance Selection for Incoming Call . . . . . . . . . 27
10.3. Outgoing Call without Appearance Seizure . . . . . . . . 31
10.4. Outgoing Call with Appearance Seizure . . . . . . . . . . 34
10.5. Outgoing Call without using an Appearance Number . . . . 38
10.6. Appearance Release . . . . . . . . . . . . . . . . . . . 40
10.7. Appearance Pickup . . . . . . . . . . . . . . . . . . . . 41
10.8. Calls between UAs within the Group . . . . . . . . . . . 45
10.9. Consultation Hold with Appearances . . . . . . . . . . . 48
10.10. Joining or Bridging an Appearance . . . . . . . . . . . . 50
10.11. Appearance Allocation - Loss of Appearance . . . . . . . 53
10.12. Appearance Seizure Contention Race Condition . . . . . . 54
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10.13. Appearance Agent Subscription to UAs . . . . . . . . . . 55
10.14. Appearance Pickup Race Condition Failure . . . . . . . . 57
10.15. Appearance Seizure Incoming/Outgoing Contention Race
Condition . . . . . . . . . . . . . . . . . . . . . . . . 60
11. Incoming Appearance Assignment . . . . . . . . . . . . . . . . 61
12. Security Considerations . . . . . . . . . . . . . . . . . . . 62
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
13.1. SIP Event Package Parameter: shared . . . . . . . . . . . 62
13.2. URN Sub-Namespace Registration: sa-dialog-info . . . . . 63
13.3. XML Schema Registration . . . . . . . . . . . . . . . . . 63
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 64
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 64
15.1. Normative References . . . . . . . . . . . . . . . . . . 64
15.2. Informative References . . . . . . . . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 66
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1. Introduction
The feature and functionality requirements for SIP user agents (UAs)
supporting business telephony applications differ greatly from basic
SIP user agents, both in terms of services and end user experience.
In addition to basic SIP support [RFC3261], many of the services in a
business environment require the support for SIP extensions such as
REFER [RFC3515], SUBSCRIBE/NOTIFY primitives
[I-D.ietf-sipcore-rfc3265bis] PUBLISH [RFC3903], the SIP Replaces
[RFC3891], and Join [RFC3911] header fields, etc. Many of the
popular business services have been documented in the SIP Service
Examples [RFC5359].
This specification details a method for implementing a group
telephony feature known variously in telephony as Bridged Line
Appearance (BLA) or Multiple Line Appearances (MLA), one of the more
popular advanced features expected of SIP IP telephony devices in a
business environment. Other names for this feature include Shared
Call/Line Appearance (SCA), Shared Call Status and Multiple Call
Appearance (MCA). A variant of this feature is known as Single Line
Extension.
This document looks at how this feature can be implemented using
standard SIP [RFC3261] in conjunction with SIP events
[I-D.ietf-sipcore-rfc3265bis] and publication [RFC3903] for
exchanging status among user agents, and the SIP dialog state event
package [RFC4235] to exchange dialog state information to achieve the
same. Different approaches will be discussed including the use of
URI parameters, feature tags, and dialog package extensions along
with the strengths and weaknesses of the various approaches.
In traditional telephony, the line is physical. A common scenario in
telephony is for a number of business telephones to share a single or
a small number of lines. The sharing or appearance of these lines
between a number of phones is what gives this feature its name. A
common scenario in SIP is for a number of business telephones to
share a single or a small number of Address of Record (AOR) URIs.
In addition, an AOR can have multiple appearances on a single UA in
terms of the user interface. The appearance number relates to the
user interface for the telephone - typically each appearance of an
AOR has a visual display (lamp that can change color or blink or a
screen icon) and a button (used to select the appearance). The
telephony concept of line appearance is still relevant to SIP due to
the user interface considerations. It is important to keep the
appearance number construct because:
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1. Human users are used to the concept and will expect it in
replacement systems (e.g. an overhead page announcement says "Joe
pickup line 3").
2. It is a useful structure for user interface representation.
The purpose of the appearance number is to identify active calls to
facilitate sharing between users (e.g. passing a call from one user
to another). If a telephone has enough buttons/lamps, calls could be
presented on the nth button. If not, it may still be desirable to
present the call state, but the appearance number should be displayed
so that users know which call, for example, is on hold on which key.
In this document, except for the usage scenarios in the next section,
we will use the term "appearance" rather than "line appearance" since
SIP does not have the concept of lines. Note that this does not mean
that a conventional telephony user interface (lamps and buttons) must
be used - implementations may use another metaphor as long as the
appearance number is readily apparent to the user. Each AOR has a
separate appearance numbering space. As a result, a given UA user
interface may have multiple occurrences of the same appearance
number, but they will be for different AORs.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119] and
indicate requirement levels for compliant mechanisms.
3. Usage Scenarios
The following examples are common applications of the Shared
Appearances feature and are mentioned here as informative use cases.
All these example usages can be supported by the Shared Appearances
feature described in this document. The main differences relate to
the user interface considerations of the device.
3.1. Executive/Assistant Arrangement
The appearances on the executive's UA also appear on the assistant's
UA. The assistant may answer incoming calls to the executive and
then place the call on hold for the executive to pick up. The
assistant can always see the state of all calls on the executive's
UA.
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3.2. Call Group
Users with similar business needs or tasks can be assigned to
specific groups and share an AOR. For example, an IT department
staff of five might answer a help line which has three appearances on
each phone in the IT work area. A call answered on one phone can be
put on hold and picked up on another phone. A shout or an IM to
another staff member can result in them taking over a call on a
particular appearance. Another phone can request to be added/joined/
bridged to an existing appearance resulting in a conference call.
3.3. Single Line Extension
In this scenario, incoming calls are offered to a group of UAs. When
one answers, the other UAs are informed. If another UA in the group
seizes the line (i.e. goes off hook), it is immediately bridged or
joined in with the call. This mimics the way residential telephone
extensions usually operate.
3.4. Changing UAs
A user is on a call on one UA and wishes to change devices and
continue the call on another UA. They place the call on hold, note
the appearance number of the call, then walk to another UA. They are
able to identify the same appearance number on the other UA, pickup
the call, and continue the conversation.
4. Requirements and Implementation
The next section details the requirements and discusses the
implementation of the shared appearances of an AOR feature.
4.1. Requirements
The basic requirements of the shared appearance feature can be
summarized as follows:
REQ-1 Incoming calls to the AOR must be offered to a group of UAs and
can be answered by any of them.
REQ-2 Each UA in the group must be able to learn the call status of
the others in the group for the purpose of rendering this information
to the user.
REQ-3 A UA must be able to join (also called bridge or conference
together) or pick up (take) an active call of another UA in the group
in a secure way.
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REQ-4 The mechanism should require the minimal amount of
configuration. UAs registering against the group AOR should be able
to participate in the appearance group without manual configuration
of group members.
REQ-5 The mechanism must scale for large numbers of appearances, n,
and large numbers of UAs, N, without introducing excessive messaging
traffic.
REQ-6 Each call or session (incoming or outgoing) must be assigned a
common "appearance" number from a managed pool administered for the
AOR group. Once the session has terminated, the appearance number is
released back into the pool and can be reused by another incoming or
outgoing session.
REQ-7 Each UA in the group must be able to learn the status of all
appearances of the group.
REQ-8 There must be mechanisms to resolve appearance contention among
the UAs in the group.
REQ-9 The mechanism must allow all UAs receiving an incoming session
request to utilize the same appearance number at the time of
alerting.
REQ-10 The mechanism must have a way of reconstructing appearance
state after an outage that does not result in excessive traffic and
processing.
REQ-11 The mechanism must have backwards compatibility such that a UA
which is unaware of the feature can still register against the group
AOR and make and receive calls.
REQ-12 The mechanism must not allow UAs outside the group to select,
seize or manipulate appearance numbers.
REQ-13 For privacy reasons, there must be a mechanism so that
appearance information is not leaked outside the group of UAs. (e.g.
"So who do you have on line 1?")
REQ-14 The mechanism must support a way for UAs to request
exclusivity on a line appearance. Exclusivity means that the UA
requesting it desires to have a private conversation with the
external party and other UAs must not be allowed to be joined or
taken. Exclusivity may be requested at the start of an incoming or
outgoing session or during the session. An exclusivity request may
be accepted or rejected by the entity providing the shared appearance
service. Therefore, the mechanism must provide a way of
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communicating the result back to the requester UA.
REQ-15 The mechanism should support a way for a UA to seize a
particular appearance number for outgoing requests prior to sending
the actual request. This is often called seizure.
REQ-16 The mechanism should support a way for a UA to seize a
particular appearance number and also send the request at the same
time. This is needed when an automatic ringdown feature (a telephone
configured to immediately dial a phone number when it goes off hook)
is combined with shared appearances - in this case, seizing the line
is the same thing as dialing.
4.2. Implementation
Many of the requirements for this service can be met using standard
SIP mechanisms such as:
- A SIP Forking Proxy and Registrar/Location Service meets REQ-1.
- The SIP Dialog Package meets REQ-2.
- The SIP Replaces and Join header fields meets REQ-3.
- The use of a State Agent for the Dialog Package meets REQ-4 and
REQ-5.
REQ-6 suggests the need for an entity which manages the appearance
resource. Just as conferencing systems commonly have a single point
of control, known as a focus, a Shared Appearance group has a single
point of control of the appearance shared resource. This is defined
as an Appearance Agent for a group. While an Appearance Agent can be
part of a centralized server, it could also be co-resident in a
member User Agent who has taken on this functionality for a group.
The Appearance Agent knows or is able to determine the dialog state
of all members of the group.
While the appearance resource could be managed co-operatively by a
group of UAs without any central control, this is outside the scope
of this draft. It is also possible that the Appearance Agent logic
could be distributed in all UAs in the group. For example, rules
that govern assigning appearance numbers for incoming requests (e.g.
lowest available appearance number) and rules for contention handling
(e.g. when two UAs request the use of the same appearance number,
hash dialog identifiers and compare with the lowest hash winning)
would need to be defined and implemented.
To best meet REQ-9, the appearance number for an incoming INVITE
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needs to be contained in the INVITE, in addition to being delivered
in the dialog package NOTIFY. Otherwise, if the NOTIFY is delayed or
lost, a UA in the group might receive an incoming INVITE but might
not know which appearance number to render during alerting.
This specification defines an extension parameter for the Alert-Info
header field in RFC 3261 to carry the appearance number:
Alert-Info: <urn:alert:service:normal>;appearance=1
The next section discusses the operations used to implement parts of
the shared appearance feature. An analysis of other mechanisms has
been performed, with the mechanism described here best meeting the
requirements of Section 4.1.
1. A UA is configured with the AOR of a shared appearance group. It
registers against the AOR, then attempts a dialog state
subscription to the AOR. If the subscription fails, loops back
to itself, or returns an error, it knows there is no State Agent,
and hence no Appearance Agent and this feature is not
implemented.
2. If the subscription receives a 200 OK, the UA knows there is a
State Agent and that the feature is implemented. The UA then
follows the steps in this list.
3. Information learned about the dialog state of other UAs in the
group is rendered to the user.
4. Incoming calls are forked to all UAs in the group, and any may
answer. UAs receive the appearance number to use in rendering
the incoming call in a NOTIFY from the Appearance Agent and in
the INVITE itself. The UA will also receive a notification if
the call is answered by another UA in the group so this
information can be rendered to the user.
5. For outgoing calls, the operation depends on the implementation.
If the user seizes a particular appearance number for the call,
the UA publishes this information and waits for a 200 OK before
sending the INVITE.
6. For outgoing calls, if the user does not seize a particular
appearance or does not care, the INVITE can be sent immediately,
and the appearance number learned as the call progresses from a
notification from the Appearance Agent.
7. For outgoing calls, if the user does not wish to seize an
appearance (such as during a consultation call or if a UA is
fetching 'service media' such as music on hold
[I-D.worley-service-example]), the UA also publishes this prior
to sending the INVITE.
8. Established calls within the group may be joined (bridged) or
taken (picked) by another UA. Information in the dialog package
notifications can be used to construct Join or Replaces header
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fields. Since the same appearance number is used for these types
of operations, this information is published prior to sending the
INVITE Join or INVITE Replaces.
9. In some cases, the Appearance Agent may not have full access to
the complete dialog state of some or all of the UAs in the group.
If this is the case, the Appearance Agent will subscribe to the
dialog state of individual UAs in the group to obtain this
information. Normal notifications will be sent every time the
dialog state changes, including calls placed, answered, placed on
and off hold, and hangups.
5. Normative Description
This section normatively describes the shared appearance feature
extensions. The following definitions are used throughout this
document:
Seizing: An appearance can be reserved prior to a call being placed
by seizing the appearance. An appearance can be seized by
communicating an artificial state of "trying" prior to actually
initiating a dialog, in order to appear as it was already initiating
a dialog. The appearance number is confirmed prior to sending the
INVITE.
Selecting(or Not-Seizing): An appearance is merely selected (i.e.,
not seized) if there is no such communication of artificial state of
"trying" prior to initiating a dialog: i.e., the state is
communicated when the dialog is actually initiated. The appearance
number is learned after the INVITE is sent. This is a user interface
only issue.
5.1. Elements
A complete system to implement this feature consists of:
1. User Agents that support publications, subscriptions, and
notifications for the SIP dialog event package, and the shared
appearance dialog package extensions and behavior.
2. An Appearance Agent consisting of a State Agent for the dialog
event package that implements an Event State Compositor (ESC) and
the shared appearance dialog package extensions and behavior.
The Appearance Agent also has logic for assigning and releasing
appearance numbers, and resolving appearance number contention.
3. A forking proxy server that can communicate with the State Agent
4. A registrar that supports the registration event package.
The behavior of these elements is described normatively in the
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following sections after the definitions of the dialog package
extensions.
5.2. Shared Appearance Dialog Package Extensions
This specification defines four new elements as extensions to the SIP
Dialog Event package [I-D.ietf-sipcore-rfc3265bis]. The schema is
defined in Section 6. The elements are <appearance>, <exclusive>,
<joined-dialog>, and <replaced-dialog> which are sub-elements of the
<dialog> element.
5.2.1. The <appearance> element
The <appearance> element is used to convey the appearance number.
The appearance number is a positive integer. When sent in a
publication in state Trying to the Appearance Agent, it is used to
request an appearance number. When sent by the Appearance Agent, it
indicates that the appearance number is associated with a dialog.
5.2.2. The <exclusive> element
The <exclusive> element is a boolean used to indicate whether the UA
will accept Join or Replaces INVITEs for this dialog. For example,
some shared appearance systems only allow call pickup when the call
is on hold. In this case, the <exclusive> element should be used to
explicitly indicate this, rather than implicitly by the hold state.
It is important to note that this element is a hint. Although a UA
may set exclusive to true, the UA must still be ready to reject an
INVITE Join relating to this dialog. Also, an INVITE Replaces might
be sent to the non-shared appearance UA to take the call. For this
reason, a UA MAY also not report full dialog identifier information
to the Appearance Agent for calls set to exclusive. If these dialog
identifiers have already been shared with the Appearance Agent, the
UA could send an INVITE Replaces to change them and then not report
the new ones to the Appearance Agent.
If the proxy knows which dialogs are marked exclusive, the proxy MAY
enforce this exclusivity by rejecting INVITE Join and INVITE Replaces
requests containing those dialog identifiers with a 403 Forbidden
response.
Note that exclusivity has nothing to do with appearance number
selection or seizing - instead, it is about call control
operations that can be performed on a dialog.
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5.2.3. The <joined-dialog> element
The <joined-dialog> element is used to convey dialog identifiers of
any other dialogs which are joined (mixed or bridged) with the
dialog. Only the UA which is performing the actual media mixing
should include this element in publications to the Appearance Agent.
Note that this element should still be used even when the Join header
field was not used to join the dialogs. For example, two separate
dialogs on a UA could be joined without any SIP call control
operations. Joined dialogs will share the same appearance number.
5.2.4. The <replaced-dialog> element
The <replaced-dialog> element is used to convey dialog identifiers of
any other dialogs which will be or have been replaced with this
dialog. For example, a UA in the group picking up a call on another
UA by sending an INVITE with Replaces would include this element for
the replacing dialog. Replaced dialogs will share the same
appearance number.
5.3. Shared Appearance User Agents
User Agents that support the Shared Appearance feature MUST support
the dialog state package [RFC4235] with the shared appearance
extensions and the 'shared' dialog event package parameter defined in
Section 11.
User Agents MUST support the dialog package extensions in Section 5.2
along with SUBSCRIBE and NOTIFY [I-D.ietf-sipcore-rfc3265bis] and
PUBLISH [RFC3903]. SUBSCRIBE, NOTIFY, and PUBLISH requests for the
dialog event package SHOULD include the 'shared' Event header field
parameter.
The presence of the 'shared' Event package parameter tells the
Appearance Agent that this UA supports this specification.
Upon initialization, the UA SHOULD subscribe to the dialog event
package of the AOR and refresh the subscription per the SIP Events
Framework. If the SUBSCRIBE request fails, loops back to itself,
then no Appearance Agent is present and this feature is not active
for this AOR. The UA MAY periodically retry the subscription to see
if conditions have changed.
User Agents which implement call pickup, joining and bridging MUST
support sending an INVITE with Replaces [RFC3891] or Join [RFC3911].
All User Agents supporting INVITE MUST support receiving an INVITE
with a Replaces [RFC3891] or a Join [RFC3911] header field.
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When publishing or notifying dialog package information, a UA MUST
include all dialog identification available at the time of
publication, with the exception that a UA may omit information if it
wishes to prevent other UAs from joining or picking up a call.
Dialog identification includes local and remote target URIs, call-id,
to-tag, and from-tag. When calls are placed on hold, the
"+sip.rendering=no" feature tag MUST be included in dialog package
notifications.
The accurate rendering of the idle/active/alerting/hold state of
other UAs in the group is an important part of the shared
appearance feature.
A UA MUST send dialog package PUBLISH requests in the following
situations:
1. When the user seizes a particular appearance number for an
outgoing call (i.e. seizing the appearance and going "off-hook",
if the UA's user interface uses this metaphor).
2. When the user has requested that an appearance number not be used
for an outgoing call (i.e. during a consultation call, a 'service
media' call such as for music on hold
[I-D.worley-service-example] or for a call not considered part of
the shared appearance group).
3. When the user has selected to join (or bridge) an existing call.
4. When the user has selected to replace (or take) an existing call.
In all these cases, the INVITE SHOULD NOT be sent until the 200 OK
response to the PUBLISH has been received, except for an emergency
call, when a UA MUST never wait for a confirmed seizure before
sending an INVITE. Instead, the emergency call MUST proceed
regardless of the status of PUBLISH transaction.
Note that when a UA seizes an appearance prior to establishment of a
dialog (#1 and #2 in above list), not all dialog information will be
available. In particular, when a UA publishes an attempt to seize an
appearance prior to knowing the destination URI, minimal or no dialog
information may be available. For example, in some cases, only the
local target URI for the call will be known and no dialog
information. If no dialog identification information is present in
the initial PUBLISH, the UA MUST PUBLISH again after receiving the
100 Trying response.
The first publication will cause the Appearance Agent to reserve
the appearance number for this UA. If the publication does not
have any dialog identifiers (e.g. Call-ID, or local tag) the
Appearance Agent cannot assign the appearance number to a
particular dialog of the UA until the second publication which
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will contain some dialog identifiers.
This publication state SHOULD be refreshed during the early dialog
state or the Appearance Agent may reassign the appearance number.
Once the dialog has transitioned to the confirmed state, no
publication refreshes are necessary.
Appearance numbers are a shorthand label for active and pending
dialogs related to an AOR. Many of the features and services built
using this extension rely on the correct rendering of this
information to the human user. In addition, the group nature of the
feature means that the rendering must be similar between different
vendors and different models. Failure to do so will greatly reduce
the value and usefulness of these protocol extensions. The
appearances number for each active and pending dialog SHOULD be
explicitly or implicitly rendered to the user. The far end identity
of each dialog (e.g. the remote party identity) MUST NOT be rendered
in place of the appearance number. The state of each appearance
SHOULD also be rendered (idle, active, busy, joined, etc.). UAs can
tell that a set of dialogs are joined (bridged or mixed) together by
the presence of one or more <joined-dialog> elements containing other
SIP dialog identifiers. Appearance numbers of dialogs can be learned
by dialog package notifications containing the <appearance> element
from the Appearance Agent or from the 'appearance' Alert-Info
parameter in an incoming INVITE. Should they conflict, the dialog
package notification takes precedence.
A UA that does not need to seize a particular appearance number (or
doesn't care) would just send an INVITE as normal to place an
outbound call.
A user may select an appearance number but then abandon placing a
call (go back on hook). In this case, the UA SHOULD free up the
appearance number by removing the event state with a PUBLISH as
described in [RFC3903].
A UA wanting to place a call but not have an appearance number
assigned publishes before sending the INVITE without an 'appearance'
element but with the 'shared' event package parameter present. If
the Appearance Agent policy does not allow calls without an assigned
appearance number, a 409 Conflict response will be received, and the
UA will republish either selecting/seizing an appearance number or
send the INVITE without publishing, in which case the Appearance
Agent will assign one.
Note that if an Appearance Agent rejects calls without an
appearance number, certain operations such as consultation calls
and music on hold may be impacted.
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When an INVITE is generated to attempt to bridge or take a call (i.e.
contains Join or Replaces with a dialog identifier of another dialog
in the shared appearance group), the appearance number of the joined
or replaced call SHOULD be published. The publication MUST contain
the appearance number of the dialog to be joined or replaced and the
dialog identifier in the 'joined-dialog' or 'replaced-dialog'
elements.
Note that this information is provided to the Appearance Agent so
that it can provide proper appearance assignment behavior. If the
INVITE Join or Replaces was sent without publishing first, the
Appearance Agent might assign a new appearance number to this
INVITE, which would be a mistake. With Join, the publication has
the 'joined-dialog' element to prevent the Appearance Agent from
generating a 409 Conflict response due to the reuse of an
appearance number. For Replaces, the purpose of the 'replaced-
dialog' is to prevent a race condition where the BYE could cause
the appearance number to be released when it should stay with the
replacing dialog.
A UA SHOULD register against the AOR only if it is likely the UA will
be answering incoming calls. If the UA is mainly going to be
monitoring the status of the shared appearance group calls and
picking or joining calls, the UA SHOULD only subscribe to the AOR and
not register against the AOR.
All subscribed UAs will received NOTIFYs of Trying state for
incoming INVITEs.
5.4. Appearance Agent
An Appearance Agent defined in this specification MUST implement a
dialog package state agent for the UAs registered against the AOR.
The Appearance Agent MUST support the appearance dialog package
extensions defined in Section 5.2. The Appearance Agent MUST support
publications and subscriptions for this event package.
The Appearance Agent MUST have a way of discovering the state of all
dialogs associated with the AOR. If this information is not
available from a call stateful proxy or B2BUA, the Appearance Agent
MAY use the registration event package [RFC3680] to learn of UAs
associated with the AOR and MAY subscribe to their dialog event
state. Also, an Appearance Agent MAY subscribe to a UAs dialog event
state in order to reconstruct state. As a result, the registrar MUST
support the registration event package. The Appearance Agent SHOULD
send dialog event state notifications whenever the following events
happen to UAs in the AOR group:
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1. A call is received, placed, answered, or terminated.
2. A call is placed on or off hold.
3. A call is joined or replaced.
4. An appearance number is reserved or released.
The Appearance Agent MUST allocate an appearance number for all
incoming calls and send immediate notifications to the UAs subscribed
to the shared group AOR. The Appearance Agent MUST be able to
communicate with the forking proxy to learn about incoming calls and
also to pass the appearance number to the proxy to insert in the
Alert-Info header field.
Note that UAs need to be able to handle incoming INVITEs without
an appearance number assigned. This could be caused by a failure
of the Appearance Agent or other error condition. Although the
proper rendering of the INVITE may not be possible, this is better
than ignoring or failing the INVITE.
An Appearance Agent SHOULD assign an appearance number to an outgoing
dialog if a PUBLISH has not been received selecting/seizing a
particular appearance number.
Note that if the appearance group has appearance-unaware UAs
making calls, the Appearance Agent will still allocate appearance
numbers for INVITEs sent by those UAs.
An Appearance Agent receiving a PUBLISH with an appearance number
checks to make sure the publication is valid. An appearance number
can be assigned to only one dialog unless there is a 'joined-dialog'
or 'replaced-dialog' element indicating that the dialog will be/has
been replaced or joined. A 409 Conflict response is returned if the
chosen appearance number is invalid, and an immediate NOTIFY should
be sent to the UA containing full dialog event state.
An Appearance Agent receiving a PUBLISH without an appearance number
but with the 'shared' event package parameter present interprets this
as a request by the UA to not assign an appearance number. If the
Appearance Agent policy does not allow this, a 409 Conflict response
is returned. If policy does allow this, a 200 OK response is
returned and no appearance number is allocated. An Appearance Agent
does not have to share this dialog information with other UAs in the
group as the information will not be rendered by the other UAs.
The Appearance Agent allocates an appearance number to a dialog from
the time the appearance is requested via a PUBLISH or from the
receipt of an INVITE, to the time when the last dialog associated
with the appearance is terminated, including all dialogs which are
joined or replaced. During the early dialog state, the Appearance
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Agent controls the rate of dialog state publication using the Expires
header field in 200 OK responses to PUBLISH requests. An interval of
3 minutes is RECOMMENDED. After the dialog associated with the
publication has been confirmed, the expiration of the publication
state has no effect on the appearance allocation. If the publication
contains no dialog state information, the Appearance Agent MUST
reserve the appearance number for the UA but can not assign the
appearance to any particular dialog of the UA. When the publication
state is updated with any dialog information, the appearance number
can then be assigned to the particular dialog. A UA which has been
allocated an appearance number using a PUBLISH MAY free up the
appearance number by removing the event state with a PUBLISH as
described in [RFC3903].
During dynamic situations, such as during a call pickup or join
action, the Appearance Agent MAY choose to implement rate limiting to
reduce the amount of notification traffic. For example, an
Appearance Agent may choose not to generate immediate NOTIFYs upon
receipt of PUBLISHes. Instead, a single NOTIFY can convey the
effects of a number of PUBLISHes, thus reducing the NOTIFY traffic
within the group.
If an INVITE is sent by a member of the group using the shared AOR or
sent to the shared AOR and no appearance number is available, the
proxy MAY reject the INVITE with a 403 Forbidden response code.
Appearance numbers are only used for dialogs in which one UA
associated with the group AOR is a participant. If an incoming
INVITE to the group AOR is forwarded to another AOR, the appearance
number is immediately freed up and can be assigned to another dialog.
6. XML Schema Definition
The 'appearance', 'joined-dialog', 'replaced-dialog', and 'exclusive'
elements are defined within a new XML namespace URI. This namespace
is "urn:ietf:params:xml:ns:sa-dialog-info". The schema for these
elements is:
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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:sa-dialog-info-info"
xmlns="urn:ietf:params:xml:ns:sa-dialog-info"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">
<xs:element name="joined-dialog" minOccurs="0"
maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="call-id" type="xs:string"
use="mandatory"/>
<xs:attribute name="local-tag" type="xs:string"
use="mandatory"/>
<xs:attribute name="remote-tag" type="xs:string"
use="mandatory"/>
</xs:complexType>
</xs:element>
<xs:element name="replaced-dialog" minOccurs="0"
maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="call-id" type="xs:string"
use="mandatory"/>
<xs:attribute name="local-tag" type="xs:string"
use="mandatory"/>
<xs:attribute name="remote-tag" type="xs:string"
use="mandatory"/>
</xs:complexType>
</xs:element>
<xs:element name="appearance" minOccurs="0" maxOccurs="1">
<xs:simpleType type="xs:integer">
</xs:simpleType>
</xs:element>
<xs:element name="exclusive" minOccurs="0" maxOccurs="1">
<xs:simpleType type="xs:boolean">
</xs:simpleType>
</xs:element>
</xs:schema>
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7. User Interface Considerations
The "appearance number" allocated to a call is an important concept
that enables calls to be handled by multiple devices with
heterogeneous user interfaces in a manner that still allows users to
see a consistent model. Careful treatment of the appearance number
is essential to meet the expectations of the users. Also, rendering
the correct call/appearance state to users is also important.
7.1. Appearance Number Rendering
Since different UAs have different user interface capabilities, it is
usual to find that some UAs have restrictions that others do not.
Perfect interoperability across all UAs is clearly not possible, but
by careful design, interoperability up to the limits of each UA can
be achieved.
The following guidelines suggest how the appearance number should be
handled in three typical user interface implementations.
7.1.1. Single Appearance UAs
These devices are constrained by only having the capability of
displaying status indications for a single appearance. Despite this,
it is important that devices of this type do not ignore the
appearance number. The UA should still send messages annotated with
an appropriate appearance number (i.e. "0"). Any call indications
for appearances other than for number "0" should be rejected with a
486 or 480 response.
7.1.2. Dual Appearance UAs
These devices are essentially single appearance phones that implement
call waiting. They have a very simple user interface that allows
them to switch between two appearances (toggle or flash hook) and
perhaps audible tones to indicate the status of the other appearance.
7.1.3. Shared Appearance UAs with Fixed Appearance Number
This UA is the typical 'business-class' hard-phone. A number of
appearances are typically configured statically and labeled on
buttons, and calls may be managed using these configured appearances.
Any calls outside this range should be ignored, and not mapped to a
free button. Users of these devices often seize specific appearance
numbers for outgoing calls, and the UA will need to seize the
appearance number and wait for confirmation from the Appearance Agent
before proceeding with calls.
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7.1.4. Shared Appearance UAs with Variable Appearance Number
This UA is typically a soft-phone or graphically rich user interface
hard-phone. In these cases, even the idea of an appearance index may
seem unnecessary. However, for these phones to be able to interwork
successfully with other phone types, it is important that they still
use the appearance index to govern the order of appearance of calls
in progress. No specific guidance on presentation is given except
that the order should be consistent. These devices can typically
make calls without waiting for confirmation from the Appearance Agent
on the appearance number.
The problems faced by each style of user interface are readily seen
in this example:
1. A call arrives at the shared appearance group, and is assigned an
appearance number of 0. All UAs should be able to render to the
user the arrival of this call.
2. Another call arrives at the shared appearance group, and is
assigned an appearance number of 1. The single appearance UA
should not present this call to the user. Other user agents
should have no problems presenting this call distinctly from the
first call.
3. The first call clears, releasing appearance number "0". The
single appearance UA should now be indicating no calls since it
is unable to manage calls other than on the first appearance.
Both shared appearance UAs should clearly show that appearance
number 0 is now free, but that there is still a call on
appearance number 1.
4. A third call arrives, and is assigned the appearance number of 0.
All UAs should be able to render the arrival of this new call to
the user. Multiple appearance UAs should continue to indicate
the presence of the second call, and should also ensure that the
presentation order is related to the appearance number and not
the order of call arrival.
7.2. Call State Rendering
UAs that implement the shared appearance feature typically have a
user interface that provides the state of other appearances in the
group. As dialog state NOTIFYs from the Appearance Agent are
processed, this information can be rendered. Even the simplest user
interface typically has three states: idle, active, and hold. The
idle state, usually indicated by lamp off, is indicated for an
appearance when the appearance number is not associated with any
dialogs, as reported by the Appearance Agent. The active state,
usually indicated by a lamp on, is indicated by an appearance number
being associated with at least one dialog, as reported by the
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Appearance Agent. The hold state, often indicated by a blinking
lamp, means the call state from the perspective of the UA in the
shared appearance group is hold. This can be determined by the
presence of the "sip+rendering=no" feature tag [RFC3840] with the
local target URI. Note that the hold state of the remote target URI
is not relevant to this display. For joined dialogs, the state is
rendered as hold only if all local target URIs are indicated with the
"sip+rendering=no" feature tag.
8. Interop with non-Shared Appearance UAs
It is desirable to allow a basic UA that does not directly support
shared appearance to be part of a shared appearance group. To
support this the Proxy must collaborate with the Appearance Agent.
This is not required in the basic shared appearance architecture,
consequently shared appearance interop with non-shared appearance UAs
will not be available in all shared appearance deployments.
First, a UA which does not support dialog events or the shared
appearance feature will be discussed. Then, a UA which does support
dialog events but not the shared appearance feature will be
discussed.
8.1. Appearance Assignment
A UA that has no knowledge of appearances must will only have
appearance numbers for outgoing calls if assigned by the Appearance
Agent. If the non-shared appearance UA does not support Join or
Replaces, all dialogs could be marked "exclusive" to indicate that
these options are not available.
8.2. Appearance Release
In all cases the Appearance Agent must be aware of dialog lifetime to
release appearances back into the group.
It is also desirable that any dialog state changes (such as hold,
etc) be made available to other UAs in the group through the Dialog
Event Package. If the Appearance Agent includes a proxy which
Record-Routes for dialogs from the non-shared appearance aware UA,
the Appearance Agent will know about the state of dialogs including
hold, etc. This information could be determined from inspection of
INVITE and re-INVITE messages and added to the dialog information
conveyed to other UAs.
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8.3. UAs Supporting Dialog Events but Not Shared Appearance
Interoperability with UAs which support dialog events but not the
shared appearance feature is more straightforward. As before, all
appearance number assignment must be done by the Appearance Agent.
The Appearance Agent can include appearance information in NOTIFYs -
this UA will simply ignore this extra information. This type of UA
will ignore appearance number limitations and may attempt to Join or
Replace dialogs marked exclusive. As a result, the Proxy or UAs may
need to reject such requests.
9. Provisioning Considerations
UAs can automatically discover if this feature is active for an AOR
by sending a SUBSCRIBE to the AOR, so no provisioning for this is
needed.
The registrar will need to be provisioned to accept either first or
third party registrations for the shared AOR. First party
registration means the To and From URIs in the REGISTER request are
the shared AOR URI. Third party registration means the To URI is the
shared AOR URI and the From URI is a different AOR, perhaps that of
the individual user. Either the credentials of the shared AOR or the
user MUST be accepted by the registrar and the Appearance Agent,
depending on the authorization policy in place for the domain.
If the Appearance Agent needs to subscribe to the dialog state of the
UAs, then the Appearance Agent and the UAs need to be provisioned
with credentials so the UAs can authenticate the Appearance Agent.
In some cases, UAs in the shared appearance group might have a UI
limitation on the number of appearances that can be rendered.
Typically this will be hard phones with buttons/lamps instead of more
flexible UIs. In this case, it can be useful for the Appearance
Agent to know this maximum number. This can allow the Appearance
Agent to apply policy when this limit is reached, e.g. deny a call.
However, this mechanism does not provide any way to discover this by
protocol means.
10. Example Message Flows
The next section shows call flow and message examples. The flows and
descriptions are non-normative. Note that in these examples, all
INVITEs sent by a UA in the group will be From the shared AOR
(sip:HelpDesk@example.com in this case), and all INVITES sent to the
group will have a Request-URI of the shared AOR. Any other requests
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would not apply to this feature and would be handled using normal SIP
mechanisms.
Note that the first twelve examples assume the Appearance Agent is
aware of dialog state events. Example 10.13 shows the case where
this is not the case and as a result the Appearance Agent initiates a
subscription to users of the shared AOR. Any of the other call flow
examples could have shown this mode of operation as it is equally
valid.
10.1. Registration and Subscription
Bob and Alice are in an appearance group identified by the shared
appearance AOR sip:HelpDesk@example.com. Bob REGISTERs using contact
sip:bob@ua2.example.com. Alice REGISTERs with contact
sip:alice@ua1.example.com.
User Agents for Alice and Bob subscribe to the dialog package for the
appearance AOR and publish dialog state to the Appearance Agent.
Message exchanges between the Registrar, Appearance Agent, Alice, and
Bob are shown below. The call flow examples below do not show the
authentication of subscriptions, publications, and notifications. It
should be noted that for security purposes, all subscriptions must be
authorized before the same is accepted.
Also note that registrations and subscriptions must all be refreshed
by Alice at intervals determined by the expiration intervals returned
by the Registrar or Appearance Agent.
Registrar Appearance Agent Alice Bob
| | | |
| | | |
|<--------------------------- REGISTER F1<| |
| | | |
|>F2 200 OK ----------------------------->| |
| | | |
| |<----- SUBSCRIBE F3<| |
| | | |
| |>F4 200 OK -------->| |
| | | |
| |>F5 NOTIFY -------->| |
| | | |
| |<-------- 200 OK F6<| |
| | | |
|<-------------------------------------------- REGISTER F7<|
| | | |
|>F8 200 OK ---------------------------------------------->|
| | | |
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| |<---------------------- SUBSCRIBE F9<|
| | | |
| |>F10 200 OK ------------------------>|
| | | |
| |>F11 NOTIFY ------------------------>|
| | | |
| |<------------------------ 200 OK F12<|
| | | |
Figure 1.
F1-F2: Alice registers AOR with
contact: <sip:alice@ua1.example.com>
F1 Alice ----> Registrar
REGISTER sip:registrar.example.com SIP/2.0
Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bK527b54da8ACC7B09
From: <sip:alice@example.com>;tag=CDF9A668-909E2BDD
To: <sip:HelpDesk@example.com>
CSeq: 2 REGISTER
Call-ID: d3281184-518783de-cc23d6bb
Contact: <sip:alice@ua1.example.com>
Max-Forwards: 70
Expires: 3600
Content-Length: 0
F2 Registrar ----> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKfbf176ef7F1D5FA2
CSeq: 2 REGISTER
Call-ID: d3281184-518783de-cc23d6bb
From: <sip:alice@example.com>;tag=CDF9A668-909E2BDD
To: <sip:HelpDesk@example.com>;tag=1664573879820199
Contact: <sip:alice@ua1.example.com>
Expires: 3600
Content-Length: 0
F3 to F6: Alice also subscribes to the events associated with the
Appearance AOR. Appearance Agent notifies Alice of the status.
F3 Alice ----> Appearance Agent
SUBSCRIBE sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKf10fac97E7A76D6A
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From: <sip:alice@example.com>;tag=925A3CAD-CEBB276E
To: <sip:HelpDesk@example.com>
CSeq: 91 SUBSCRIBE
Call-ID: ef4704d9-bb68aa0b-474c9d94
Contact: <sip:alice@ua1.example.com>
Event: dialog;shared
Accept: application/dialog-info+xml
Max-Forwards: 70
Expires: 3700
Content-Length: 0
F4 Appearance Agent ----> Alice
SIP/2.0 200 OK
Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKf10fac97E7A76D6A
CSeq: 91 SUBSCRIBE
Call-ID: ef4704d9-bb68aa0b-474c9d94
From: <sip:alice@example.com>;tag=925A3CAD-CEBB276E
To: <sip:HelpDesk@example.com>;tag=1636248422222257
Allow-Events: dialog
Expires: 3700
Contact: <sip:appearanceagent.example.com>
Content-Length: 0
F5 Appearance Agent ----> Alice
NOTIFY sip:alice@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=1636248422222257
To: <sip:alice@example.com>;tag=925A3CAD-CEBB276E
Call-ID: ef4704d9-bb68aa0b-474c9d94
CSeq: 232 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1846
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
version="40"
state="full"
entity="sip:HelpDesk@example.com">
</dialog-info>
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F6 Alice ----> Appearance Agent
SIP/2.0 200 OK
Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1846
From: <sip:HelpDesk@example.com>;tag=1636248422222257
To: <sip:alice@example.com>;tag=925A3CAD-CEBB276E
CSeq: 232 NOTIFY
Call-ID: ef4704d9-bb68aa0b-474c9d94
Contact: <sip:alice@ua1.example.com>
Event: dialog;shared
Content-Length: 0
F7 Bob ----> Registrar
REGISTER sip:registrar.example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4b53b54d87B
From: <sip:bob@example.com>;tag=34831131
To: <sip:HelpDesk@example.com>
CSeq: 72 REGISTER
Call-ID: 139490230230249348
Contact: <sip:bob@ua2.example.com>
Max-Forwards: 70
Expires: 3600
Content-Length: 0
F8 Registrar ----> Bob
SIP/2.0 200 OK
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4b53b54d87B
From: <sip:bob@example.com>;tag=34831131
To: <sip:HelpDesk@example.com>;tag=fkwlwqi1
CSeq: 72 REGISTER
Call-ID: 139490230230249348
Contact: <sip:alice@ua1.example.com>;expires=3200
Contact: <sip:bob@ua2.example.com>;expires=3600
Content-Length: 0
10.2. Appearance Selection for Incoming Call
In the call flow below Bob and Alice are in an appearance group.
Carol places a call to the appearance group AOR. The Appearance
Agent sends NOTIFYs to Alice and Bob telling them what appearance the
call is using. Both Alice and Bob's devices are alerted of the
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incoming call. Bob answers the call.
Note that it is possible that both Alice and Bob answer the call and
send 200 OK responses to Carol. It is up to Carol to resolve this
situation. Typically, Carol will send ACKs to both 200 OKs but send
a BYE to terminate one of the dialogs. As a result, either Alice or
Bob will receive the BYE and publish that their dialog is over.
However, if Carol answers both Alice and Bob and keeps both dialogs
active, then the Appearance Agent will need to resolve the situation
by moving either Alice or Bob's dialog to a different appearance.
All NOTIFY messages in the call flow below carry dialog events and
only dialog states are mentioned for simplicity. For brevity, the
details of some messages are not shown below. Note that the order of
F2 - F5 and F7 - F8 could be reversed.
Forking Appearance
Carol Proxy Agent Alice Bob
| | | | |
|>F1 INVITE >| | | |
| |< - - - - - >| | |
| | |>F2 NOTIFY ----------->|
| | | | |
| | |<F3 200 OK -----------<|
| | | | |
| | |>F4 NOTIFY ->| |
| | | | |
| | |<-200 OK F5-<| |
|<- 100 F6 -<| | | |
| |>F7 INVITE (appearance=1) ---------->|
| | | | |
| |>F8 INVITE (appearance=1) >| |
| | | | |
| |<-------------------- Ringing 180 F9<|
|< 180 F10 -<| | | |
| |<--------- 180 Ringing F11<| |
|< 180 F12 -<| | | |
| | | | |
| |<------------------------ 200 OK F13<|
|< 200 F14 -<| | | |
| | | | |
| |>F15 CANCEL -------------->| |
| | | | |
| |<-------------- 200 OK F16<| |
| | | | |
| |<Request Cancelled 487 F17<| |
| | | | |
| |>F18 ACK ----------------->| |
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|>F19 ACK -->| | | |
| |>F20 ACK --------------------------->|
| | | | |
|<=============Both way RTP established===========>|
| | | | |
| |< - - - - - >| | |
| | | | |
| | |>F21 NOTIFY >| |
| | | | |
| | |<- 200 F22 -<| |
| | | | |
| | |>F23 NOTIFY ---------->|
| | | | |
| | |<F24 200 OK ----------<|
| | | |
Figure 2.
F4 Appearance Agent ----> Alice
NOTIFY sip:alice@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=151702541050937
To: <sip:alice@example.com>;tag=18433323-C3D237CE
Call-ID: 1e361d2f-a9f51109-bafe31d4
CSeq: 12 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1403
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="13"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="2a7294823093f5274e3fd2ec54a2d76c"
call-id="14-1541707345"
remote-tag="44BAD75D-E3128D42"
direction="recipient">
<sa:appearance>1</sa:appearance>
<state>trying</state>
<remote>
<identity>sip:carol@ua.example.com</identity>
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</remote>
</dialog>
</dialog-info>
F7 Proxy ----> Bob
INVITE sip:bob@ua2.example.com SIP/2.0
Via: SIP/2.0/UDP ua3.example.com;branch=z9hG4bK4324ea
Via: SIP/2.0/UDP proxy.example.com;branch=z9hG4bK38432ji
From: <sip:carol@example.com>;tag=44BAD75D-E3128D42
To: <sip:HelpDesk@example.com>
CSeq: 106 INVITE
Call-ID: 14-1541707345
Contact: <sip:carol@ua3.example.com>
Max-Forwards: 69
Alert-Info: <urn:alert:service:normal>;appearance=1
Content-Type: application/sdp
Content-Length: ...
v=0
o=- 1102980499 1102980499 IN IP4 ua3.example.com
s=
c=IN IP4 ua3.example.com
t=0 0
m=audio 2238 RTP/AVP 0 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
F21 Appearance Agent ----> Alice
NOTIFY sip:alice@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=151702541050937
To: <sip:alice@example.com>;tag=18433323-C3D237CE
Call-ID: 1e361d2f-a9f51109-bafe31d4
CSeq: 12 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK1403
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
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xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="13"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="2a7294823093f5274e3fd2ec54a2d76c"
call-id="14-1541707345"
remote-tag="44BAD75D-E3128D42"
local-tag="7349dsfjkFD03s"
direction="recipient">
<sa:appearance>1</sa:appearance>
<state>confirmed</state>
<local>
<target>sip:bob@ua2.example.com</target>
</local>
<remote>
<identity>sip:carol@ua.example.com</identity>
</remote>
</dialog>
</dialog-info>
10.3. Outgoing Call without Appearance Seizure
In this scenario, Bob's UA places a call without first selecting/
seizing an appearance number. After Bob sends the INVITE, the
appearance assigns an appearance number for it and notifies both
Alice and Bob.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | | |
| |<------------------------------------- INVITE F1<|
| | | | |
| |>F2 100 Trying --------------------------------->|
|<-- INVITE F3<| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<-- NOTIFY F4<| |
| | | | |
| | |>F5 200 OK -->| |
| | | |------- NOTIFY F6>|
| | | | |
| | | |<F7 200 OK ------<|
|>F8 180 ---->| | | |
| |>F9 180 Ringing -------------------------------->|
| | | | |
| |< - - - - - - - - - - - - - ->| |
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| | | | |
| | |<- NOTIFY F10<| |
| | | | |
| | |>F11 200 OK ->| |
| | | |------ NOTIFY F12>|
| | | | |
| | | |<F13 200 OK -----<|
|>F14 200 OK ->| | | |
| |>F15 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F16<|
|<---- ACK F17<| | | |
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F18<| |
| | | | |
| | |>F19 200 OK ->| |
| | | |------ NOTIFY F20>|
| | | | |
| | | |<F21 200 OK -----<|
| | | | |
Figure 3.
F1 Bob ----> Proxy
INVITE sip:carol@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK98c87c52123A08BF
From: <sip:HelpDesk@example.com>;tag=15A3DE7C-9283203B
To: <sip:carol@example.com>
CSeq: 1 INVITE
Call-ID: f3b3cbd0-a2c5775e-5df9f8d5
Contact: <sip:bob@ua2.example.com>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 223
v=0
o=- 1102980499 1102980499 IN IP4 ua2.example.com
s=IP SIP UA
c=IN IP4 ua2.example.com
t=0 0
a=sendrecv
m=audio 2236 RTP/AVP 0 8 101
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a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
F4 Appearance Agent ----> Alice
NOTIFY sip:alice@ua1.example.com SIP/2.0
Via: SIP/2.0/UDP appearanceagent.example.com;branch=z9hG4bK81d84f62
From: <sip:HelpDesk@example.com>;tag=1636248422222257
To: <sip:alice@example.com>;tag=925A3CAD-CEBB276E
Call-ID: ef4704d9-bb68aa0b-474c9d94
CSeq: 233 NOTIFY
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="27"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="fa02538339df3ce597f9e3e3699e28fc"
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
local-tag="15A3DE7C-9283203B" direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
</dialog>
</dialog-info>
F6 Appearance Agent ----> Bob
NOTIFY sip:bob@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=497585728578386
To: <sip:bob@example.com>;tag=633618CF-B9C2EDA4
Call-ID: a7d559db-d6d7dcad-311c9e3a
CSeq: 7 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com
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;branch=z9hG4bK1711759878512309
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <sip:appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="27"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="fa02538339df3ce597f9e3e3699e28fc"
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
local-tag="15A3DE7C-9283203B" direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
</dialog>
</dialog-info>
10.4. Outgoing Call with Appearance Seizure
In this scenario, Bob's UA sends out a dialog event PUBLISH with
state (trying) selecting/seizing an appearance number before sending
the INVITE. After receiving the 200 OK from the Appearance Agent
confirming the appearance number, Bob's UA sends the INVITE to Carol
and establishes a session. For brevity, details of some of the
messages are not included in the message flows.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | |<----- PUBLISH F1<|
| | | | |
| | | |>F2 200 OK ------>|
| | | | |
| | |<-- NOTIFY F3<| |
| | | | |
| | |>F4 200 OK -->| |
| | | |------- NOTIFY F5>|
| | | | |
| | | |<F6 200 OK ------<|
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| | | | |
| |<------------------------------------- INVITE F7<|
| | | | |
| |>F8 100 Trying --------------------------------->|
|<-- INVITE F9<| | | |
| | | |<---- PUBLISH F10<|
| | | | |
| | | |>F11 200 OK ----->|
| | | | |
|>F12 180 --->| | | |
| |>F13 180 Ringing ------------------------------->|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F14<| |
| | | | |
| | |>F15 200 OK ->| |
| | | |------ NOTIFY F16>|
| | | | |
| | | |<F17 200 OK -----<|
|>F18 200 OK ->| | | |
| |>F19 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F20<|
|<---- ACK F21<| | | |
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F22<| |
| | | | |
| | |>F23 200 OK ->| |
| | | |------ NOTIFY F24>|
| | | | |
| | | |<F25 200 OK -----<|
| | | | |
Figure 4.
F1 to F4: Bob uses the shared appearance of the Help Desk on his UA
to place an outgoing call (e.g., he goes off-hook). Before sending
the outgoing INVITE request, Bob publishes to the Appearance Agent
reserving appearance number 1. The Appearance Agent notifies Alice
(and all other UAs, including Bob) of the event by sending NOTIFYs.
F1 Bob ----> Appearance Agent
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PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79
From: <sip:bob@example.com>;tag=44150CC6-A7B7919D
To: <sip:HelpDesk@example.com>
CSeq: 7 PUBLISH
Call-ID: 44fwF144-F12893K38424
Contact: <sip:bob@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="6"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83" direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
</dialog>
</dialog-info>
F2 Appearance Agent ----> Bob
SIP/2.0 200 OK
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79
From: <sip:bob@example.com>;tag=44150CC6-A7B7919D
To: <sip:HelpDesk@example.com>
CSeq: 7 PUBLISH
Call-ID: 44fwF144-F12893K38424
Contact: <sip:bob@ua2.example.com>
Event: dialog;shared
SIP-Etag: 482943245
Allow-Events: dialog
Expires: 60
Content-Length: 0
F7 Bob ---> Proxy
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INVITE sip:carol@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK342122
Max-Forwards: 70
From: <sip:HelpDesk@example.com>;tag=15A3DE7C-9283203B
To: <sip:carol@example.com>
Call-ID: f3b3cbd0-a2c5775e-5df9f8d5
CSeq: 31 INVITE
Contact: <sip:bob@ua2.example.com>
Content-Type: application/sdp
Content-Length: ...
(SDP Not Shown)
F10 Bob ----> Appearance Agent
PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK6d644638E7
From: <sip:bob@example.com>;tag=0CCf6-A7FdsB79D
To: <sip:HelpDesk@example.com>
CSeq: 437 PUBLISH
Call-ID: fwF14d4-F1FFF2F2893K38424
Contact: <sip:bob@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="6"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83"
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
local-tag="15A3DE7C-9283203B"
direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
<remote>
<identity uri="sip:carol@example.com">
</identity>
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</remote>
</dialog>
</dialog-info>
10.5. Outgoing Call without using an Appearance Number
In this scenario, Bob's UA sends out a dialog event PUBLISH with
state (trying) indicating that he does not want to utilize an
appearance number for this dialog. The PUBLISH does not have an
appearance element but does have the 'shared' dialog event parameter.
As a result, the Appearance Agent knows the UA does not wish to use
an appearance number for this call. If the Appearance Agent does not
wish to allow this, it would reject the PUBLISH with a 409 Conflict
response and the UA would know to re-PUBLISH selecting/seizing an
appearance number.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | |<----- PUBLISH F1<|
| | | | |
| | | |>F2 200 OK ------>|
| | | | |
| | |<-- NOTIFY F3<| |
| | | | |
| | |>F4 200 OK -->| |
| | | |------- NOTIFY F5>|
| | | | |
| | | |<F6 200 OK ------<|
| | | | |
| |<------------------------------------- INVITE F7<|
| | | | |
| |>F8 100 Trying --------------------------------->|
|<-- INVITE F9<| | | |
| | | |<---- PUBLISH F10<|
| | | | |
| | | |>F11 200 OK ----->|
| | | | |
|>F12 180 --->| | | |
| |>F13 180 Ringing ------------------------------->|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F14<| |
| | | | |
| | |>F15 200 OK ->| |
| | | |------ NOTIFY F16>|
| | | | |
| | | |<F17 200 OK -----<|
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|>F18 200 OK ->| | | |
| |>F19 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F20<|
|<---- ACK F21<| | | |
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F22<| |
| | | | |
| | |>F23 200 OK ->| |
| | | |------ NOTIFY F24>|
| | | | |
| | | |<F25 200 OK -----<|
| | | | |
Figure 5.
F1 Bob ----> Appearance Agent
PUBLISH sip:appearanceagent.example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bK61314d6446383E79
From: <sip:bob@example.com>;tag=4415df82k39sf
To: <sip:HelpDesk@example.com>
CSeq: 7 PUBLISH
Call-ID: 44fwF144-F12893K38424
Contact: <sip:bob@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="6"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83" direction="initiator">
<sa:exclusive>false</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
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</dialog>
</dialog-info>
Note that F7 would be the same as the previous example.
10.6. Appearance Release
Bob and Carol are in a dialog, created, for example as in Section
10.3. Carol sends a BYE to Bob to terminate the dialog and the
Appearance Agent de-allocates the appearance number used, sending
notifications out to the UAs in the shared group.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
|>F22 BYE ---->| | | |
| |>F23 BYE --------------------------------------->|
| | | | |
| |<------------------------------------ 200 OK F24<|
|<--200 OK F25<| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F26<| |
| | | | |
| | |>F27 200 OK ->| |
| | | |------ NOTIFY F28>|
| | | | |
| | | |<F29 200 OK -----<|
Figure 6.
F28 Appearance Agent ----> Bob
NOTIFY sip:bob@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=497585728578386
To: <sip:bob@example.com>
Call-ID: a7d559db-d6d7dcad-311c9e3a
CSeq: 7 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com
;branch=z9hG4bK759878512309
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <sip:appearanceagent.example.com>
Content-Length: ...
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<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="27"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="fa02538339df3ce597f9e3e3699e28fc"
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
local-tag="15A3DE7C-9283203B"
remote-tag="65a98f7c-1dd2-11b2-88c6-b0316298f7c"
direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>terminated</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
</dialog>
</dialog-info>
10.7. Appearance Pickup
In this scenario, Bob has an established dialog with Carol created
using the call flows of Figure 1 or Figure 2. Bob then places Carol
on hold. Alice receives a notification of this and renders this on
Alice's UI. Alice subsequently picks up the held call and has a
established session with Carol. Finally, Carol hangs up. Alice must
PUBLISH F32 to indicate that the INVITE F38 will be an attempt to
pickup the dialog between Carol and Bob, and hence may use the same
appearance number.
Carol Proxy Alice Appearance Agent Bob
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |<------------------------------(hold) INVITE F22<|
|<- INVITE F23<| | | |
| | | | |
|>F24 200 OK ->| | | |
| |>F25 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F26<|
|<---- ACK F27<| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F28<| |
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| | | | |
| | |>F29 200 OK ->| |
| | | |>F30 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F31<|
| | | | |
| | Alice decides to pick up the call |
| | | | |
| | |>F32 PUBLISH->| |
| | | | |
| | |<- 200 OK F33<| |
| | | | |
| | |<- NOTIFY F34<| |
| | | | |
| | |>F35 200 OK ->| |
| | | |>F36 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F37<|
| |<-- INVITE F38<| | |
|<- INVITE F39<|(w/ Replaces) | | |
|( w/ Replaces)| | | |
|>F40 200 OK ->| | | |
| |>F41 200 OK -->| | |
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | | |>F42 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F43<|
| | |<- NOTIFY F44<| |
| | | | |
| | |>F45 200 OK ->| |
| | | | |
| |<----- ACK F46<| | |
|<---- ACK F47<| | | |
| | | | |
|<= Both way RTP established =>| | |
| | | | |
|>F48 BYE ---->| | | |
| |>F49 BYE --------------------------------------->|
| | | | |
| |<------------------------------------ OK 200 F50<|
|<- 200 OK F51<| | | |
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F52<| |
| | | | |
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| | |>F53 200 OK ->| |
| | | | |
| | | |>F54 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F55<|
Figure 7.
F28 Appearance ----> Alice
NOTIFY sip:alice@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=151702541050937
To: <sip:alice@example.com>;tag=18433323-C3D237CE
Call-ID: 1e361d2f-a9f51109-bafe31d4
CSeq: 12 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com
;branch=z9hG4bK1403
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <sip:appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83"
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
local-tag="15A3DE7C-9283203B"
remote-tag="65a98f7c-1dd2-11b2-88c6-b0316298f7c"
direction="initiator">
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<state>active</state>
<local>
<target uri="sip:bob@ua2.example.com">
<param pname="+sip.rendering" pval="no"/>
</target>
</local>
<remote>
<identity>sip:carol@example.com</identity>
<target uri="sip:carol@ua3.example.com" />
</remote>
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</dialog>
</dialog-info>
F32 Alice ----> Appearance Agent
PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A
From: <sip:HelpDesk@example.com>;tag=44150CC6-A7B7919D
To: <sip:alice@example.com>;tag=428765950880801
CSeq: 11 PUBLISH
Call-ID: 87837Fkw87asfds
Contact: <sip:alice@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83"
call-id="3d57cd17-47deb849-dca8b6c6"
local-tag="8C4183CB-BCEAB710" >
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<sa:replaced-dialog
call-id="f3b3cbd0-a2c5775e-5df9f8d5"
from-tag="15A3DE7C-9283203B"
to-tag="65a98f7c-1dd2-11b2-88c6-b03162323164+65a98f7c" />
<state>trying</state>
<local>
<target uri="sip:alice@ua1.example.com">
<param pname="+sip.rendering" pval="yes"/>
</target>
</local>
<remote>
<target uri="sip:carol@ua3.example.com" />
</remote>
</dialog>
</dialog-info>
F38 Alice ----> Proxy
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INVITE sip:carol@example.com SIP/2.0
Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bK4ea695b5B376A60C
From: <sip:HelpDesk@example.com>;tag=8C4183CB-BCEAB710
To: <sip:carol@example.com:5075>
CSeq: 1 INVITE
Call-ID: 3d57cd17-47deb849-dca8b6c6
Contact: <sip:alice@ua1.example.com>
<all-one-line>
Replaces: f3b3cbd0-a2c5775e-5df9f8d5;to-tag=65a98f7c
-1dd2-11b2-88c6-b03162323164+65a98f7c;from-tag=15A3DE7C-9283203B
</all-one-line>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 223
v=0
o=- 1102980497 1102980497 IN IP4 ua1.example.com
s=IP SIP UA
c=IN IP4 ua1.example.com
t=0 0
a=sendrecv
m=audio 2238 RTP/AVP 0 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
10.8. Calls between UAs within the Group
In this scenario, Bob calls Alice who is also in the Appearance
group. Only one appearance number is used for this dialog. This
example also shows the use of the 'exclusive' tag to indicate that
other UAs in the group can not join or take this dialog.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| |<-------------------- INVITE (to Alice's UA) F1<|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | | | |
| | |<-- NOTIFY F2<| |
| | | | |
| | |>F3 200 OK -->| |
| | | |>F4 NOTIFY ------>|
| | | | |
| | | |<------ 200 OK F5<|
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| |>F6 INVITE --->| | |
| | (appearance=1)| | |
| | | | |
| |<------ 180 F7<| | |
| | | | |
| |>F8 180 --------------------------------------->|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<-- NOTIFY F9<| |
| | | | |
| | |>F10 200 OK ->| |
| | | |>F11 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F12<|
| |<-- 200 OK F13<| | |
| | | | |
| |>F14 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F15<|
| | | | |
| |>F16 ACK ----->| | |
| | | | |
| | |<======= RTP established =======>|
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F17<| |
| | | | |
| | |>F18 200 OK ->| |
| | | |>F19 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F24<|
| | | | |
Figure 8.
F19 Appearance Agent ----> Bob
NOTIFY sip:bob@ua1.example.com SIP/2.0
From: <sip:HelpDesk@example.com>;tag=497585728578386
To: <sip:bob@example.com>;tag=633618CF-B9C2EDA4
Call-ID: a7d559db-d6d7dcad-311c9e3a
CSeq: 7 NOTIFY
Via: SIP/2.0/UDP appearanceagent.example.com
;branch=z9hG4bK1711759878512309
Max-Forwards: 70
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Content-Type: application/dialog-info+xml
Event: dialog;shared
Subscription-State: active
Contact: <sip:appearanceagent.example.com>
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="3xdsd4f9c83"
call-id="b3cbd0-ad2c5775e-5df9f8d5"
local-tag="34322kdfr234f"
remote-tag="3153DE7C-928203B"
direction="initiator">
<sa:exclusive>true</sa:exclusive>
<sa:appearance>1</sa:appearance>
<state>confirmed</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
<remote>
<identity>sip:HelpDesk@example.com</identity>
<target uri="sip:alice@ua1.example.com" />
</remote>
</dialog>
<dialog id="4839589"
call-id="b3cbd0-ad2c5775e-5df9f8d5"
local-tag="3153DE7C-928203B"
remote-tag="34322kdfr234f"
direction="responder">
<sa:exclusive>true</sa:exclusive>
<sa:appearance>1</sa:appearance>
<state>confirmed</state>
<local>
<target uri="sip:alice@ua1.example.com" />
</local>
<remote>
<identity>sip:HelpDesk@example.com</identity>
<target uri="sip:bob@ua2.example.com" />
</remote>
</dialog>
</dialog-info>
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10.9. Consultation Hold with Appearances
In this scenario, Bob has a call with Carol. Bob makes a
consultation call to Alice by putting Carol on hold and calling
Alice. Bob chooses not to have an appearance number for the call to
Alice since he is treating it as part of the call to Carol. He
indicates this in his PUBLISH F32 which contains the 'shared' Event
parameter but no <appearance> element. The PUBLISH is sent before
the INVITE to Alice to ensure no appearance number is assigned by the
Appearance Agent. Finally, Bob hangs up with Alice and resumes the
call with Carol. Note that the Appearance Agent does not generate
notifications on the dialog state of the consultation call.
Note that if Carol hangs up while Bob is consulting with Alice, Bob
can decide if he wants to reuse the appearance number used with Carol
for the call with Alice. If not, Bob publishes the termination of
the dialog with Carol and the Appearance Agent will re-allocate the
appearance. If he wants to keep the appearance, Bob will publish the
termination of the dialog with Carol and also publish the appearance
with the dialog with Alice. This will result in Bob keeping the
appearance number until he reports the dialog with Alice terminated.
Note that the call flow would be similar if Bob called a music on
hold server instead of Alice to implement a music on hold service as
described in [I-D.worley-service-example].
Carol Proxy Alice Appearance Agent Bob
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |<------------------------------(hold) INVITE F22<|
|<- INVITE F23<| | | |
| | | | |
|>F24 200 OK ->| | | |
| |>F25 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F26<|
|<---- ACK F27<| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F28<| |
| | | | |
| | |>F29 200 OK ->| |
| | | |>F30 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F31<|
| | | | |
| | Bob makes a consultation call to Alice |
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| | | | |
| | | |<---- PUBLISH F32<|
| | | | |
| | | |>F33 200 OK ----->|
| | | | |
| |<------------------------------------ INVITE F34<|
| | | | |
| |>F35 INVITE -->| | |
| | | | |
| |<-- 200 OK F36<| | |
| | | | |
| |>F37 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F38<|
| | | | |
| |>F39 ACK ----->| | |
| | | | |
| | |<======= RTP established =======>|
| | | | |
| | Bob hangs up with Alice |
| | | | |
| |<--------------------------------------- BYE F40<|
| | | | |
| |>F41 BYE ----->| | |
| | | | |
| |<-- 200 OK F42<| | |
| | | | |
| |>F43 200 OK ------------------------------------>|
| | | | |
| |<----------------------------(unhold) INVITE F44<|
|<- INVITE F45<| | | |
| | | | |
|>F46 200 OK ->| | | |
| |>F47 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F48<|
|<---- ACK F49<| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F50<| |
| | | | |
| | |>F51 200 OK ->| |
| | | |>F52 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F53<|
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
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Figure 9.
F32 Bob ----> Appearance Agent
PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A
From: <sip:bob@example.com>;tag=44150CC6-A7B7919D
To: <sip:HelpDesk@example.com>;tag=428765950880801
CSeq: 11 PUBLISH
Call-ID: 44fwF144-F12893K38424
Contact: <sip:bob@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83"
call-id="b3cbd0-ad2c5775e-5df9f8d5"
local-tag="3153DE7C-928203B"
direction="initiator">
<sa:exclusive>true</sa:exclusive>
<state>trying</state>
<local>
<target uri="sip:bob@ua2.example.com">
</target>
</local>
<remote>
<identity>sip:HelpDesk@example.com</identity>
<target uri="sip:alice@ua1.example.com" />
</remote>
</dialog>
</dialog-info>
10.10. Joining or Bridging an Appearance
In this call flow, a call answered by Bob is joined by Alice or
"bridged". The Join header field is used by Alice to request this
bridging. If Bob did not support media mixing, Bob could obtain
conferencing resources as described in [RFC4579].
Carol Forking Proxy Appearance Agent Alice Bob
| | | | |
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|<=============Both way RTP established===========>|
| | | | |
| | |< PUBLISH F22| |
| | | | |
| | |>F23 200 OK >| |
| | | | |
| |<---- INVITE (w/ Join) F24<| |
| | | | |
| |>F25 INVITE (w/Join)---------------->|
| | | | |
| |<---- OK 200 Contact:Bob;isfocus F26<|
| | | | |
| |< - - - - - >| | |
| | | | |
| | |>F27 NOTIFY >| |
| | | | |
| | |< 200 OK F28<| |
| | | | |
| | |>F29 NOTIFY ---------->|
| | | | |
| | |<F30 200 OK ----------<|
| | | | |
| |>F31 200 OK Contact:B----->| |
| | | | |
| |<----------------- ACK F32<| |
| | | | |
| |>ACK F33---------------------------->|
| | | | |
| |<-----INVITE Contact:Bob;isfocus F34<|
|<-INVITE F35| | | |
| | | | |
|>F26 200 -->| | | |
| |>F37 200 OK ------------------------>|
| | | | |
| |<--------------------------- ACK F38<|
|<--- ACK F39| | | |
| | | |<==RTP==>|
|<=============Both way RTP established===========>|
| | | | |
| |< - - - - - >| | |
| | | | |
| | |>F40 NOTIFY >| |
| | | | |
| | |< 200 OK F41<| |
| | | | |
| | |>F42 NOTIFY ---------->|
| | | | |
| | |<F43 200 OK ----------<|
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| | | | |
Figure 10.
F22 Alice ----> Appearance Agent
PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A
From: <sip:alice@example.com>;tag=44150CC6-A7B7919D
To: <sip:HelpDesk@example.com>;tag=428765950880801
CSeq: 11 PUBLISH
Call-ID: 87837Fkw87asfds
Contact: <sip:alice@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com:5060">
<dialog id="id3d4f9c83"
call-id="dc95da63-60db1abd-d5a74b48"
local-tag="605AD957-1F6305C2" >
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<sa:joined-dialog
call-id="14-1541707345"
from-tag="44BAD75D-E3128D42"
to-tag="d3b06488-1dd1-11b2-88c5-b03162323164+d3e48f4c" />
<state>trying</state>
<local>
<target uri="sip:alice@ua1.example.com">
</target>
</local>
<remote>
<target uri="sip:bob@example.com" />
</remote>
</dialog>
</dialog-info>
F24 Alice ----> Proxy
INVITE sip:bob@ua.example.com SIP/2.0
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Via: SIP/2.0/UDP ua1.example.com;branch=z9hG4bKcc9d727c2C29BE31
From: <sip:HelpDesk@example.com>;tag=605AD957-1F6305C2
To: <sip:bob@ua.example.com>
CSeq: 2 INVITE
Call-ID: dc95da63-60db1abd-d5a74b48
Contact: <sip:alice@ua1.example.com>
<all-one-line>
Join: 14-1541707345;to-tag=d3b06488-1dd1-11b2-88c5
-b03162323164+d3e48f4c;from-tag=44BAD75D-E3128D42
</all-one-line>
Max-Forwards: 70
Content-Type: application/sdp
Content-Length: 223
v=0
o=- 1103061265 1103061265 IN IP4 ua1.example.com
s=IP SIP UA
c=IN IP4 ua1.example.com
t=0 0
a=sendrecv
m=audio 2236 RTP/AVP 0 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
10.11. Appearance Allocation - Loss of Appearance
Bob reserves an appearance with a PUBLISH, sends an INVITE to Carol,
then becomes unreachable. When he fails to refresh his publication
to the appearance agent, the Appearance Agent declares the dialog
terminated and frees up the appearance using NOTIFYs F14 and F16.
After retransmitting the NOTIFY to Bob (in not shown messages F17,
F18, etc.), the subscription is terminated.
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Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | |<----- PUBLISH F1<|
| | | | |
| | | |>F2 200 OK ------>|
| | | | |
| | |<-- NOTIFY F3<| |
| | | | |
| | |>F4 200 OK -->| |
| | | |------- NOTIFY F5>|
| | | | |
| | | |<F6 200 OK ------<|
| | | | |
| |<------------------------------------- INVITE F7<|
| | | | |
| |>F8 100 Trying --------------------------------->|
|<-- INVITE F9<| | | |
| | | |<---- PUBLISH F10<|
| | | | |
| | | |>F11 200 OK ----->|
| | | | |
|>F12 180 --->| | | |
| |>F13 180 Ringing ------------------------------->|
| | | | |
| | | | Bob goes offline |
| | | | |
| | | Appearance selection times out |
| | | | |
| | |<- NOTIFY F14<| |
| | | | |
| | |>F15 200 OK ->| |
| | | |------ NOTIFY F16>|
| | | | |
| | | NOTIFY is retransmitted |
Figure 11.
10.12. Appearance Seizure Contention Race Condition
Bob and Alice both try to reserve appearance 2 by publishing at the
same time. The Appearance Agent allocates the appearance to Bob by
sending a 200 OK and denies it to Alice by sending a 409 Conflict.
After the NOTIFY F5, Alice learns that Bob is using appearance 2.
Alice then attempts to reserve appearance 3 by publishing, which is
then accepted.
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Carol Proxy Alice Appearance Agent Bob
| | | | |
| | | |<----- PUBLISH F1<|
| | | | (appearance=2)
| | |>F2 PUBLISH ->| |
| | | (appearance=2) |
| | | | |
| | | |>F3 200 OK ------>|
| | |<---- F4 409 <| |
| | | | |
| | |<-- NOTIFY F5<| |
| | | | |
| | |>F6 200 OK -->| |
| | | |------- NOTIFY F7>|
| | | | |
| | | |<F8 200 OK ------<|
| | | | |
| |<------------------------------------- INVITE F9<|
| | | | |
| |>F10 100 Trying -------------------------------->|
|<- INVITE F11<| | | |
| | | |<---- PUBLISH F12<|
| | | | (appearance=2)
| | | |>F13 200 OK ----->|
| | |>F14 PUBLISH->| |
| | | (appearance=3) |
| | | | |
| | |<--- F15 200 <| |
| | | | |
| | |<- NOTIFY F16<| |
| | | | |
| |>F17 200 OK ->| |
Dave | | |------ NOTIFY F18>|
| | | | |
| | | |<F19 200 OK -----<|
| |<-- INVITE F20<| | |
| | | | |
| |>F21 100 ----->| | |
|<- INVITE F22<| | | |
Figure 12.
10.13. Appearance Agent Subscription to UAs
In this scenario, the Appearance Agent does not have any way of
knowing Bob's dialog state information, except through Bob. This
could be because the Appearance Agent is not part of a B2BUA, or
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perhaps Bob is remotely registering. When Bob registers, the
Appearance Agent receives a registration event package notification
from the registrar. The Appearance Agent then SUBSCRIBEs to Bob's
dialog event state using Event:dialog in the SUBSCRIBE. Whenever
Bob's dialog state changes, a NOTIFY is sent to the Appearance Agent
who then notifies the other other UAs in the group.
Carol Proxy Alice Appearance Agent Bob
| | | | |
| |<----------------------------------- REGISTER F1<|
| | | | |
| |>F2 200 OK ------------------------------------->|
| | | | |
| |>F3 NOTIFY ------------------>| |
| | | | |
| |<------------------ 200 OK F4<| |
| | | |---- SUBSCRIBE F5>|
| | | | |
| | | |<F6 200 OK ------<|
| | | | |
| | | |<------ NOTIFY F7<|
| | | | |
| | | |>F8 200 OK ------>|
| | | | |
| | | |<--- SUBSCRIBE F9<|
| | | | |
| | | |>F10 200 OK ----->|
| | | | |
| | | |------ NOTIFY F11>|
| | | | |
| | | |<F12 200 OK -----<|
| | | | |
| |<------------------------------------ INVITE F13<|
| | | | |
| |>F14 100 Trying -------------------------------->|
|<- INVITE F15<| | | |
| | | |<----- NOTIFY F16<|
| | | | |
| | | |>F17 200 OK ----->|
| | |<- NOTIFY F18<| |
| | | | |
| | |>F19 200 OK ->| |
| | | |------ NOTIFY F20>|
| | | | |
| | | |<F21 200 OK -----<|
|>F22 180 --->| | | |
| |>F23 180 Ringing ------------------------------->|
| | | | |
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| | | |<----- NOTIFY F24<|
| | | | |
| | | |>F25 200 OK ----->|
| | |<- NOTIFY F26<| |
| | | | |
| | |>F27 200 OK ->| |
| | | |------ NOTIFY F28>|
| | | | |
| | | |<F29 200 OK -----<|
|>F30 200 OK ->| | | |
| |>F31 200 OK ------------------------------------>|
| | | | |
| | | |<----- NOTIFY F32<|
| | | | |
| | | |>F33 200 OK ----->|
| | | | |
| |<--------------------------------------- ACK F34<|
|<---- ACK F35<| | | |
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| | |<- NOTIFY F36<| |
| | | | |
| | |>F37 200 OK ->| |
| | | |------ NOTIFY F38>|
| | | | |
| | | |<F39 200 OK -----<|
| | | | |
Figure 13.
10.14. Appearance Pickup Race Condition Failure
In this scenario, Bob has an established dialog with Carol created
using the call flows of Figure 1 or Figure 2. Bob then places Carol
on hold. Alice receives a notification of this and renders this on
Alice's UI. Alice attempts to pick up the call but Carol hangs up
before the pickup can complete. Alice cancels the pickup attempt
with the PUBLISH F48. Note that the call flow for a failed Join
would be almost identical.
Carol Proxy Alice Appearance Agent Bob
| | | | |
|<================= Both way RTP established ===================>|
| | | | |
| |<------------------------------(hold) INVITE F22<|
|<- INVITE F23<| | | |
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| | | | |
|>F24 200 OK ->| | | |
| |>F25 200 OK ------------------------------------>|
| | | | |
| |<--------------------------------------- ACK F26<|
|<---- ACK F27<| | | |
| | | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |<- NOTIFY F28<| |
| | | | |
| | |>F29 200 OK ->| |
| | | |>F30 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F31<|
| | | | |
| | Alice decides to pick up the call |
| | | | |
| | |>F32 PUBLISH->| |
| | | | |
| | |<- 200 OK F33<| |
| | | | |
| | |<- NOTIFY F34<| |
| | | | |
| | |>F35 200 OK ->| |
| | | |>F36 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F37<|
|>F38 BYE ---->| | | |
| |>F39 BYE --------------------------------------->|
| | | | |
| |<------------------------------------ OK 200 F40<|
|<- 200 OK F41<| | | |
| |<-- INVITE F42<| | |
|<- INVITE F43<|(w/ Replaces) | | |
|( w/ Replaces)| | | |
| | | | |
|>F44 481 ---->| | | |
| |>F45 481 ----->| | |
|<---- ACK F46<| | | |
| |<----- ACK F47<| | |
| | |>F48 PUBLISH->| |
| | | | |
| | |<- 200 OK F49<| |
| | | | |
| | |<- NOTIFY F50<| |
| | | | |
| | |>F51 200 OK ->| |
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| | | |>F52 NOTIFY ----->|
| | | | |
| | | |<----- 200 OK F53<|
Figure 14.
F48 Alice ----> Appearance Agent
PUBLISH sip:HelpDesk@example.com SIP/2.0
Via: SIP/2.0/UDP ua2.example.com;branch=z9hG4bKa5d6cf61F5FBC05A
From: <sip:alice@example.com>;tag=44150CC6-A7B7919D
To: <sip:HelpDesk@example.com>;tag=428765950880801
CSeq: 11 PUBLISH
Call-ID: 87837Fkw87asfds
Contact: <sip:alice@ua2.example.com>
Event: dialog;shared
Max-Forwards: 70
Content-Type: application/dialog-info+xml
Content-Length: ...
<?xml version="1.0"?>
<dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
xmlns:sa="urn:ietf:params:xml:ns:sa-dialog-info"
version="10"
state="partial"
entity="sip:HelpDesk@example.com">
<dialog id="id3d4f9c83"
call-id="dc95da63-60db1abd-d5a74b48"
local-tag="605AD957-1F6305C2" >
<sa:appearance>1</sa:appearance>
<sa:exclusive>false</sa:exclusive>
<sa:replaced-dialog
call-id="14-1541707345"
from-tag="44BAD75D-E3128D42"
to-tag="d3b06488-1dd1-11b2-88c5-b03162323164+d3e48f4c" />
<state>terminated</state>
<local>
<target uri="sip:alice@ua1.example.com">
</target>
</local>
<remote>
<target uri="sip:carol@ua3.example.com" />
</remote>
</dialog>
</dialog-info>
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10.15. Appearance Seizure Incoming/Outgoing Contention Race Condition
Alice tries to seize appearance 2 at the same time appearance 2 is
allocated to an incoming call. The Appearance Agent resolves the
conflict by sending a 409 Conflict to Alice. After the NOTIFY F6,
Alice learns that the incoming call is using appearance 2. Alice
republishes for appearance 3, which is accepted. Note that this
example shows the INVITE being received before the NOTIFY from the
Appearance Agent.
Carol Proxy Alice Appearance Agent Bob
| | | | |
|>-- INVITE F1>| | | |
| |< - - - - - - - - - - - - - ->| |
| | | | |
| | |>F2 PUBLISH ->| |
| | | (appearance=2) |
| | | | |
| |>F3 INVITE (appearance=2) ---------------------->|
| | | | |
| |>F4 INVITE | | |
| |(appearance=2)>| | |
| | |<---- F5 409 <| |
| | | | |
| | |<-- NOTIFY F6<| |
| | | | |
| | |>F7 200 OK -->| |
| | | |------- NOTIFY F8>|
| | | | |
| | | |<F9 200 OK ------<|
| | | | |
| | |>F10 PUBLISH->| |
| | | (appearance=3) |
| | | | |
| | |< F11 200 OK <| |
| | | | |
| | |<- NOTIFY F12<| |
| | | | |
| |>F13 200 OK ->| |
Dave | | |------ NOTIFY F14>|
| | | | |
| | | |<F15 200 OK -----<|
| |<-- INVITE F16<| | |
| | | | |
| |>F17 100 ----->| | |
|<- INVITE F18<| | | |
Figure 15.
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11. Incoming Appearance Assignment
A proxy inserting an 'appearance' Alert-Info parameter follows normal
policies Alert-Info policies. If an Alert-Info is already present,
the proxy either removes the Alert-Info if it is not trusted, or adds
the 'appearance' parameter to the Alert-Info header field. If an
appearance number parameter is already present (associated with
another AOR or by mistake), the value is rewritten adding the new
appearance number. There MUST NOT be more than one appearance
parameter in an Alert-Info header field.
If no special ringtone is desired, a normal ringtone should be
indicated using the urn:alert:service:normal in the Alert-Info, as
per [I-D.liess-dispatch-alert-info-urns]. The appearance number
present in an Alert-Info header field SHOULD be rendered by the UA to
the user, following the guidelines in Section 5.3. If the INVITE is
forwarded to another AOR, the appearance parameter in the Alert-Info
SHOULD be removed before forwarding outside the group.
The determination as to what value to use in the appearance parameter
can be done at the proxy that forks the incoming request to all the
registered UAs.
There are a variety of ways the proxy can use to determine what
value it should use to populate this parameter. For example, the
proxy could fetch this information by initiating a SUBSCRIBE
request with Expires: 0 to the Appearance Agent for the AOR to
fetch the list of lines that are in use. Alternatively, it could
act like a UA that is a part of the appearance group and SUBSCRIBE
to the State-Agent like any other UA. This would ensure that the
active dialog information is available without having to poll on a
need basis. It could keep track of the list of active calls for
the appearance AOR based on how many unique INVITE requests it has
forked to or received from the appearance AOR. Another approach
would be for the Proxy to first send the incoming INVITE to the
Appearance Agent which would redirect to the appearance group URI
and escape the proper Alert-Info header field for the Proxy to
recurse and distribute to the other UAs in the group.
The Appearance Agent needs to know about all incoming requests to
the AOR in order to seize the appearance number. One way in which
this could be done is for the Appearance Agent to register against
the AOR with a higher q value. This will result in the INVITE
being sent to the Appearance Agent first, then being offered to
the UAs in the group.
The changes to RFC 3261 ABNF are:
alert-param = LAQUOT absoluteURI RAQUOT *( SEMI (generic-param /
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appearance-param) )
appearance-param = "appearance" EQUAL *DIGIT
12. Security Considerations
Since multiple line appearance features are implemented using
semantics provided by [RFC3261], Event Package for Dialog State as
define in , and Event Notification [I-D.ietf-sipcore-rfc3265bis],
[RFC3903], security considerations in these documents apply to this
draft as well.
Specifically, since dialog state information and the dialog
identifiers are supplied by UA's in an appearance group to other
members, the same is prone to "call hijacks". For example, a rogue
UA could snoop for these identifiers and send an INVITE with Replaces
header containing these call details to take over the call. As such
INVITES with Replaces header MUST be authenticated using the standard
mechanism (like Digest or S/MIME) described in [RFC3261]. before it
is accepted. NOTIFY or PUBLISH message bodies that provide the
dialog state information and the dialog identifiers MAY be encrypted
end-to-end using the standard mechanics. All SUBSCRIBES between the
UA's and the Appearance Agent MUST be authenticated.
13. IANA Considerations
This section registers the SIP event package parameter 'shared', the
SIP Alert-Info header field parameter "appearance" and the XML
namespace extensions to the SIP Dialog Package.
13.1. SIP Event Package Parameter: shared
This specification defines a new event parameter 'shared' for the
Dialog Package. When used in a NOTIFY, it indicates that the
notifier supports the shared appearance feature. When used in a
PUBLISH, it indicates that the publisher has explicit appearance
information contained in the message body. If not present in a
PUBLISH, the Appearance Agent MAY assign an appearance number to any
new dialogs in the message body.
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13.2. URN Sub-Namespace Registration: sa-dialog-info
This section registers a new XML namespace per the procedures
in [RFC3688].
URI: urn:ietf:params:xml:ns:sa-dialog-info.
Registrant Contact: IETF BLISS working group, <bliss@ietf.org>,
Alan Johnston <alan.b.johnston@gmail.com>
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Shared Appearance Dialog Information Namespace</title>
</head>
<body>
<h1>Namespace for Shared Appearance Dialog Information</h1>
<h2>urn:ietf:params:xml:ns:dialog-info</h2>
<p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfcXXXX.txt">
RFCXXXX</a>.</p>
</body>
</html>
END
13.3. XML Schema Registration
This section registers an XML schema per the procedures in
[RFC3688].
URI: urn:ietf:params:xml:schesa:sa-dialog-info.
Registrant Contact: IETF BLISS working group, <bliss@ietf.org>,
Alan Johnston <alan.b.johnston@gmail.com>
The XML for this schema can be found in Section 6.
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14. Acknowledgements
The following individuals were part of the shared appearance Design
team and have provided input and text to the document (in
alphabetical order):
Martin Dolly, Andrew Hutton, Raj Jain, Fernando Lombardo, Derek
MacDonald, Bill Mitchell, Michael Procter, Theo Zowzouvillys.
Thanks to Chris Boulton for helping with the XML schema.
Much of the material has been drawn from previous work by Mohsen
Soroushnejad, Venkatesh Venkataramanan, Paul Pepper and Anil Kumar,
who in turn received assistance from:
Kent Fritz, John Weald, and Sunil Veluvali of Sylantro Systems, Steve
Towlson, and Michael Procter of Citel Technologies, Rob Harder and
Hong Chen of Polycom Inc, John Elwell, J D Smith of Siemens
Communications, Dale R. Worley of Pingtel, Graeme Dollar of Yahoo
Inc.
Also thanks to Geoff Devine, Paul Kyzivat, Jerry Yin, John Elwell,
Dan York, Spenser Dawkins, Martin Dolly, and Brett Tate for their
comments.
Thanks to Carolyn Beeton, Francois Audet, Andy Hutton, Tim Ross, Raji
Chinnappa, and Harsh Mendiratta for their detailed review of the
document.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] 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.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[I-D.ietf-sipcore-rfc3265bis]
Roach, A., "SIP-Specific Event Notification",
draft-ietf-sipcore-rfc3265bis-01 (work in progress),
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February 2010.
[RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension
for Event State Publication", RFC 3903, October 2004.
[RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
Protocol (SIP) "Replaces" Header", RFC 3891,
September 2004.
[RFC4235] Rosenberg, J., Schulzrinne, H., and R. Mahy, "An INVITE-
Initiated Dialog Event Package for the Session Initiation
Protocol (SIP)", RFC 4235, November 2005.
[RFC3911] Mahy, R. and D. Petrie, "The Session Initiation Protocol
(SIP) "Join" Header", RFC 3911, October 2004.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[I-D.liess-dispatch-alert-info-urns]
Liess, L., Alexeitsev, D., Jesske, R., Johnston, A., and
A. Siddiqui, "Alert-Info URNs for the Session Initiation
Protocol (SIP)", draft-liess-dispatch-alert-info-urns-02
(work in progress), July 2010.
15.2. Informative References
[RFC5359] Johnston, A., Sparks, R., Cunningham, C., Donovan, S., and
K. Summers, "Session Initiation Protocol Service
Examples", BCP 144, RFC 5359, October 2008.
[RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol
(SIP) Call Control - Conferencing for User Agents",
BCP 119, RFC 4579, August 2006.
[RFC3680] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", RFC 3680, March 2004.
[I-D.worley-service-example]
Worley, D., "Session Initiation Protocol Service Example
-- Music on Hold", draft-worley-service-example-05 (work
in progress), July 2010.
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Authors' Addresses
Alan Johnston (editor)
Avaya
St. Louis, MO 63124
Email: alan.b.johnston@gmail.com
Mohsen Soroushnejad
Sylantro Systems Corp
Email: mohsen.soroush@sylantro.com
Venkatesh Venkataramanan
Sylantro Systems Corp
Email: vvenkatar@gmail.com
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