RFC 7865
Session Initiation Protocol (SIP) Recording Metadata
Pages: 34
Proposed Standard
Proposed Standard
Part 1 of 2 – Pages 1 to 22
Internet Engineering Task Force (IETF) R. Ravindranath Request for Comments: 7865 Cisco Systems Category: Standards Track P. Ravindran ISSN: 2070-1721 Nokia Networks P. Kyzivat Huawei May 2016 Session Initiation Protocol (SIP) Recording MetadataAbstract
Session recording is a critical requirement in many communications environments, such as call centers and financial trading organizations. In some of these environments, all calls must be recorded for regulatory, compliance, and consumer protection reasons. The recording of a session is typically performed by sending a copy of a media stream to a recording device. This document describes the metadata model as viewed by the Session Recording Server (SRS) and the recording metadata format. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7865.
Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents
1. Introduction ....................................................3 2. Terminology .....................................................3 3. Definitions .....................................................4 4. Metadata Model ..................................................5 5. Recording Metadata Format from SRC to SRS .......................6 5.1. XML Data Format ............................................7 5.1.1. Namespace ...........................................7 5.1.2. 'recording' Element .................................7 6. Recording Metadata Classes ......................................7 6.1. Recording Session ..........................................8 6.1.1. Attributes ..........................................8 6.1.2. Linkages ............................................9 6.2. Communication Session Group ................................9 6.2.1. Attributes .........................................10 6.2.2. Linkages ...........................................10 6.3. Communication Session .....................................11 6.3.1. Attributes .........................................11 6.3.2. Linkages ...........................................12 6.4. CS-RS Association .........................................13 6.4.1. Attributes .........................................14 6.4.2. Linkages ...........................................14 6.5. Participant ...............................................14 6.5.1. Attributes .........................................15 6.5.2. Linkages ...........................................15 6.6. Participant-CS Association ................................16 6.6.1. Attributes .........................................17 6.6.2. Linkages ...........................................17 6.7. Media Stream ..............................................18 6.7.1. Attributes .........................................18 6.7.2. Linkages ...........................................19
6.8. Participant-Stream Association ............................19
6.8.1. Attributes .........................................20
6.8.2. Linkages ...........................................20
6.9. Syntax of XML Elements for Date and Time ..................21
6.10. Format of Unique ID ......................................21
6.11. Metadata Version Indicator ...............................21
7. Recording Metadata Snapshot Request Format .....................22
8. SIP Recording Metadata Examples ................................23
8.1. Complete SIP Recording Metadata Example ...................23
8.2. Partial Update of Recording Metadata XML Body .............25
9. XML Schema Definition for Recording Metadata ...................26
10. Security Considerations .......................................30
11. IANA Considerations ...........................................31
11.1. SIP Recording Metadata Schema Registration ...............31
12. References ....................................................31
12.1. Normative References .....................................31
12.2. Informative References ...................................32
Acknowledgements ..................................................34
Authors' Addresses ................................................34
1. Introduction
Session recording is a critical requirement in many communications
environments, such as call centers and financial trading
organizations. In some of these environments, all calls must be
recorded for regulatory, compliance, and consumer protection reasons.
The recording of a session is typically performed by sending a copy
of a media stream to a recording device. This document focuses on
the recording metadata, which describes the Communication Session
(CS). The document describes a metadata model as viewed by the
Session Recording Server (SRS) and the recording metadata format, the
requirements for which are described in [RFC6341] and the
architecture for which is described in [RFC7245].
2. Terminology
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 [RFC2119]. This
document only uses these key words when referencing normative
statements in existing RFCs.
3. Definitions
Metadata model: A metadata model is an abstract representation of metadata using a Unified Modeling Language (UML) [UML] class diagram. Metadata classes: Each block in the model represents a class. A class is a construct that is used as a blueprint to create instances (called "objects") of itself. The description of each class also has a representation of its attributes in a second compartment below the class name. Attributes: Attributes represent the elements listed in each of the classes. The attributes of a class are listed in the second compartment below the class name. Each instance of a class conveys values for the attributes of that class. These values get added to the recording's metadata. Linkages: Linkages represent the relationship between the classes in the model. Each linkage represents a logical connection between classes (or objects) in class diagrams (or object diagrams). The linkages used in the metadata model of this document are associations. This document also refers to the terminology defined in [RFC6341].
4. Metadata Model
Metadata is the information that describes recorded media and the CS to which they relate. The diagram below shows a model for metadata as viewed by an SRS. +-------------------------------+ 1..* | Recording Session (RS) |----+ +-------------------------------+ | | 1..* | 1..* | | | | | | 0..* | | +-----------------+ | +------------+ | | Communication | | | CS-RS | | | Session Group | | | Association|--+ | (CS-Group) | | | | | +-----------------+ | +------------+ | | 0..1 | | | | | 0..* | 1..* | +-------------------------------+ | | Communication Session (CS) | | | | | +-------------------------------+ | | 1..* | 0..1 | +-----+ | | | | 0..* | 0..* | 0..* | +-------------+ receives +----------------+ | | | Participant |----------| Media Stream |--+ | | |0..* 0..*| | | | | | | | | | | | | | | sends | | | | |----------| | | | |1.* 0..*| | | +-------------+ +----------------+ | | | | | | | +------------------------+------------+ | | | | | +------------------+ +----------------------+ | |Participant-CS | | Participant-Stream | +-----------| Association | | Association | | | | | +------------------+ +----------------------+
The metadata model is a class diagram in UML. The model describes the structure of metadata in general by showing the classes, their attributes, and the relationships among the classes. Each block in the model above represents a class. The linkages between the classes represent the relationships, which can be associations or compositions. The metadata is conveyed from the Session Recording Client (SRC) to the SRS. The model allows metadata describing CSs to be communicated to the SRS as a series of snapshots, each representing the state as seen by a single SRC at a particular instant in time. Metadata changes from one snapshot to another reflect changes in what is being recorded. For example, if a participant joins a conference, then the SRC sends the SRS a snapshot of metadata having that participant information (with attributes like (Name, AoR) tuple and associate-time). (Note: "AoR" means "Address-of-Record".) Some of the metadata is not required to be conveyed explicitly from the SRC to the SRS, if it can be obtained contextually by the SRS (e.g., from SIP or Session Description Protocol (SDP) signaling). For example, the 'label' attribute within the 'stream' XML element references an SDP "a=label" attribute that identifies an m-line within the Recording Session (RS) SDP. The SRS would learn the media properties from the media line.5. Recording Metadata Format from SRC to SRS
This section gives an overview of the recording metadata format. Some data from the metadata model is assumed to be made available to the SRS through SDP [RFC4566], and therefore this data is not represented in the XML document format specified in this document. SDP attributes describe different media formats like audio and video. The other metadata attributes, such as participant details, are represented in a new recording-specific XML document of type 'application/rs-metadata+xml'. The SDP "label" attribute [RFC4574] provides an identifier by which a metadata XML document can refer to a specific media description in the SDP sent from the SRC to the SRS. The XML document format can be used to represent either the complete metadata or a partial update to the metadata. The latter includes only elements that have changed compared to the previously reported metadata.
5.1. XML Data Format
Every recording metadata XML document sent from the SRC to the SRS contains a 'recording' element. The 'recording' element acts as a container for all other elements in this XML document. A 'recording' object is an XML document. It has the XML declaration and contains an encoding declaration in the XML declaration, e.g., "<?xml version="1.0" encoding="UTF-8"?>". If the charset parameter of the MIME content type declaration is present and it is different from the encoding declaration, the charset parameter takes precedence. Every application conforming to this specification MUST accept the UTF-8 character encoding to ensure minimal interoperability. Syntax and semantic errors in an XML document should be reported to the originator, using application-specific mechanisms.5.1.1. Namespace
With the following URN, this document defines a new namespace URI for elements defined herein: urn:ietf:params:xml:ns:recording:15.1.2. 'recording' Element
The 'recording' element MUST contain an xmlns namespace attribute with a value of urn:ietf:params:xml:ns:recording:1. Exactly one 'recording' element MUST be present in every recording metadata XML document. A 'recording' element MAY contain a 'dataMode' element indicating whether the XML document is a complete document or a partial update. If no 'dataMode' element is present, then the default value is "complete".6. Recording Metadata Classes
This section describes each class of the metadata model and the attributes of each class. This section also describes how different classes are linked and the XML element for each of them.
6.1. Recording Session
+-------------------------------+ | Recording Session (RS) | +-------------------------------+ | | 1..* 0..* | start-time |-------------- Media Stream | end-time | | | | | +-------------------------------+ | 1..* | 1..* | | | 0..* | 0..* Communication Communication Session (CS) Session Group (CS-Group) Each instance of an RS class, namely the RS object, represents a SIP session created between an SRC and SRS for the purpose of recording a CS. The RS object is represented in the XML schema using the 'recording' element, which in turn relies on the SIP/SDP session with which the XML document is associated to provide the attributes of the RS element.6.1.1. Attributes
An RS class has the following attributes: o start-time - Represents the start time of an RS object. o end-time - Represents the end time of an RS object. 'start-time' and 'end-time' attribute values are derivable from the Date header (if present in the SIP message) in the RS. In cases where the Date header is not present, 'start-time' is derivable from the time at which the SRS receives the notification of the SIP message to set up the RS, and 'end-time' is derivable from the time at which the SRS receives a disconnect on the RS SIP dialog.
6.1.2. Linkages
Each instance of an RS has: o Zero or more instances of CS-Groups. o Zero or more instances of CS objects. o Zero or more instances of MediaStream objects. Zero instances of CSs and CS-Groups in a 'recording' element are allowed to accommodate persistent recording scenarios. A persistent RS is a SIP dialog that is set up between the SRC and the SRS, even before any CS is set up. The metadata sent from the SRC to the SRS when the persistent RS SIP dialog is set up may not have any CS (and the related CS-Group) elements in the XML, as there may not be a session that is associated to the RS yet. For example, a phone acting as an SRC can set up an RS with the SRS, possibly even before the phone is part of a CS. Once the phone joins a CS, the same RS would be used to convey the CS metadata.6.2. Communication Session Group
Recording Session (RS) | 1..* | | 0..* +-------------------------------+ | Communication Session | | Group (CS-Group) | +-------------------------------+ | group_id | | associate-time | | disassociate-time | | | +-------------------------------+ | 0..1 | | 1..* Communication Session (CS) One instance of a CS-Group class, namely the CS-Group object, provides association or grouping of all related CSs. For example, in a contact center flow, a call can get transferred to multiple agents. Each of these can trigger the setup of a new CS. In cases where the SRC knows the related CSs, it can group them using the CS-Group element. The CS-Group object is represented in the XML schema using the 'group' element.
6.2.1. Attributes
A CS-Group has the following attributes: o group_id - This attribute groups different CSs that are related. The SRC (or the SRS) is responsible for ensuring the uniqueness of 'group_id' in cases where multiple SRCs interact with the same SRS. The mechanism by which the SRC groups the CS is outside the scope of this document. o associate-time - This is the time when a grouping is formed. The rules that determine how a grouping of different CS objects is done by the SRC are outside the scope of this document. o disassociate-time - 'disassociate-time' for the CS-Group is calculated by the SRC as the time when the grouping ends.6.2.2. Linkages
The linkages between a CS-Group class and other classes are associations. A CS-Group is associated with the RS and CS in the following manner: o There are one or more RS objects per CS-Group. o Each CS-Group object has to be associated with one or more RSs. Here, each RS can be set up by the potentially different SRCs. o There are one or more CSs per CS-Group (for example, in cases where the call is transferred). A CS cannot be associated with more than one CS-Group.
6.3. Communication Session
Recording Communication Session (RS) Session Group (CS-Group) | 1..* | 0..1 | | | 0..* | 1..* +-------------------------------+ | Communication Session (CS) | +-------------------------------+ | session_id | | sipSessionID | | reason | | group-ref | | start-time | | stop-time | +-------------------------------+ | | | 0..* | 0..1 | | | 0..* | 0..* Participant Media Stream A CS class and its object in the metadata model represent the CS and its properties as seen by the SRC. The CS object is represented in the XML schema using the 'session' element.6.3.1. Attributes
A CS class has the following attributes: o session_id - This attribute is used to uniquely identify an instance of a CS object, namely the 'session' XML element within the metadata XML document. 'session_id' is generated using the rules mentioned in Section 6.10. o reason - This represents the reason why a CS was terminated. The value for this attribute is derived from the SIP Reason header [RFC3326] of the CS. There MAY be multiple instances of the 'reason' XML element inside a 'session' element. The 'reason' XML element has 'protocol' as an attribute, which indicates the protocol from which the reason string is derived. The default value for the 'protocol' attribute is "SIP". The 'reason' element can be derived from a SIP Reason header in the CS.
o sipSessionID - This attribute carries a SIP Session-ID as defined
in [SessionID]. Each CS object can have zero or more
'sipSessionID' elements. More than one 'sipSessionID' attribute
may be present in a CS. For example, if three participants -- A,
B, and C -- are in a conference that has a focus acting as an SRC,
the metadata sent from the SRC to the SRS will likely have three
'sipSessionID' elements that correspond to the SIP dialogs that
the focus has with each of the three participants.
o group-ref - A 'group-ref' attribute MAY be present to indicate the
group (identified by 'group_id') to which the enclosing session
belongs.
o start-time - This optional attribute represents the start time of
the CS as seen by the SRC.
o stop-time - This optional attribute represents the stop time of
the CS as seen by the SRC.
This document does not specify attributes relating to what should
happen to a recording of a CS after it has been delivered to the SRS
(e.g., how long to retain the recording, what access controls to
apply). The SRS is assumed to behave in accordance with its local
policy. The ability of the SRC to influence this policy is outside
the scope of this document. However, if there are implementations
where the SRC desires to specify its own policy preferences, this
information could be sent as extension data attached to the CS.
6.3.2. Linkages
A CS is linked to the CS-Group, participant, MediaStream (MS), and
RS classes by using the association relationship. The association
between the CS and the participant allows the following:
o A CS will have zero or more participants.
o A participant is associated with zero or more CSs. This includes
participants who are not directly part of any CS. An example of
such a case is participants in a pre-mixed media stream. The SRC
may have knowledge of such participants but not have any signaling
relationship with them. This might arise if one participant in a
CS is a conference focus. To summarize, even if the SRC does not
have direct signaling relationships with all participants in a CS,
it should nevertheless create a participant object for each
participant that it knows about.
o The model also allows participants in a CS that are not
participants in the media. An example is the identity of a Third
Party Call Control (3pcc) that has initiated a CS to two or more
participants in the CS. Another example is the identity of a
conference focus. Of course, a focus is probably in the media,
but since it may only be there as a mixer, it may not report
itself as a participant in any of the media streams.
The association between the CS and the media stream allows the
following:
o A CS will have zero or more streams.
o A stream can be associated with at most one CS. A stream in a
persistent RS is not required to be associated with any CS before
the CS is created, and hence the zero association is allowed.
The association between the CS and the RS allows the following:
o Each instance of an RS has zero or more instances of CS objects.
o Each CS has to be associated with one or more RSs. Each RS can be
potentially set up by different SRCs.
6.4. CS-RS Association
1..* 0..*
Recording Communication
Session ----------+---------- Session
|
|
|
+-----------------------+
| CS-RS Association |
| |
+-----------------------+
| associate-time |
| disassociate-time |
| session_id |
+-----------------------+
The CS-RS Association class describes the association of a CS to an
RS for a period of time. A single CS may be associated with
different RSs (perhaps by different SRCs) and may be associated and
dissociated several times.
The CS-RS Association class is represented in XML using the
'sessionrecordingassoc' XML element.
6.4.1. Attributes
The CS-RS Association class has the following attributes: o associate-time - associate-time is calculated by the SRC as the time it sees a CS associated to an RS. o disassociate-time - disassociate-time is calculated by the SRC as the time it sees a CS disassociate from an RS. o session_id - Each instance of this class MUST have a 'session_id' attribute that identifies the CS to which this association belongs.6.4.2. Linkages
The CS-RS Association class is linked to the CS and RS classes.6.5. Participant
Communication Session (CS) | 0..* | | 0..* +-------------------------------+ | Participant | +-------------------------------+ | nameID | | participant_id | | | +-------------------------------+ | 0..* 1..* | receives| |sends | 0..* 0..* | Media Stream A participant class and its objects have information about a device that is part of a CS and/or contributes/consumes media stream(s) belonging to a CS. The participant object is represented in the XML schema using the 'participant' element.
6.5.1. Attributes
A participant class has two attributes: o nameID - This attribute is a list of (Name, AoR) tuples. An AoR (Section 6 of [RFC3261]) can be either a SIP/SIPS/tel URI ("SIPS" means "SIP Secure"; the tel URI is discussed in [RFC3966]), a Fully Qualified Domain Name (FQDN), or an IP address. For example, the AoR may be drawn from the From header field or the P-Asserted-Identity header [RFC3325] field. The SRC's local policy is used to decide where to draw the AoR from. The Name parameter represents the participant name (SIP display name) or dialed number (when known). Multiple tuples are allowed for cases where a participant has more than one AoR. For example, a P-Asserted-Identity header can have both SIP and tel URIs. o participant_id - This attribute is used to identify the 'participant' XML element within the XML document. It is generated using the rules mentioned in Section 6.10. This attribute MUST be used for all references to a participant within a CS-Group, and MAY be used to reference the same participant more globally. This document does not specify other attributes relating to participants (e.g., participant role, participant type). An SRC that has information regarding these attributes can provide this information as part of extension data to the 'participant' XML element from the SRC to the SRS.6.5.2. Linkages
The participant class is linked to the MS and CS classes by using an association relationship. The association between the participant and the MS allows the following: o A participant will receive zero or more media streams. o A participant will send zero or more media streams. (The same participant provides multiple streams, e.g., audio and video.)
o A media stream will be received by zero or more participants. It
is possible, though perhaps unlikely, that a stream is generated
but sent only to the SRC and SRS, not to any participant -- for
example, in conferencing where all participants are on hold and
the SRC is collocated with the focus. Also, a media stream may be
received by multiple participants (e.g., "whisper" calls, side
conversations).
o A media stream will be sent by one or more participants (pre-mixed
streams).
An example of a case where a participant receives zero or more
streams is where a supervisor may have a side conversation with an
agent while the agent converses with a customer.
6.6. Participant-CS Association
1..* 0..*
Communication
Session -----------+----------- Participant
|
|
|
+---------------------------+
| Participant-CS Association|
| |
| |
+---------------------------+
| associate-time |
| disassociate-time |
| param |
| participant_id |
| session_id |
+---------------------------+
The Participant-CS Association class describes the association of a
participant to a CS for a period of time. A participant may be
associated to and dissociated from a CS several times (for example,
connecting to a conference, then disconnecting, then connecting
again).
The Participant-CS Association object is represented in the XML
schema using the 'participantsessionassoc' element.
6.6.1. Attributes
The Participant-CS Association class has the following attributes: o associate-time - associate-time is calculated by the SRC as the time it sees a participant associated to a CS. o disassociate-time - disassociate-time is calculated by the SRC as the time it sees a participant disassociate from a CS. It is possible that a given participant can have multiple associate times / disassociate times within a given communication session. o param - The capabilities here are those that are indicated in the Contact header as defined in Section 9 of [RFC3840]. For example, in a CS (which can be a conference), you can have participants who are playing the role of "focus". These participants do not contribute to media in the CS; however, they switch the media received from one participant to every other participant in the CS. Indicating the capabilities of the participants (here, "focus") would be useful for the recorder to learn about these kinds of participants. The capabilities are represented using the 'param' XML element in the metadata. The 'param' XML element encoding defined in [RFC4235] is used to represent the capability attributes in metadata. Each participant may have zero or more capabilities. A participant may use different capabilities, depending on the role it plays at a particular instance -- for example, if a participant moves across different CSs (e.g., due to transfer) or is simultaneously present in different CSs with different roles. o participant_id - This attribute identifies the participant to which this association belongs. o session_id - This attribute identifies the session to which this association belongs.6.6.2. Linkages
The Participant-CS Association class is linked to the participant and CS classes.
6.7. Media Stream
Participant | 0..* 1..* | receives| |sends | 0..* 0..* | +-------------------------+ | Media Stream | 0..1 0..* +-------------------------+ Communication ------------| | Session | label | | content-type | | stream_id | | session_id | +-------------------------+ 0..* | | | 1..* | Recording Session A MS class (and its objects) has the properties of media as seen by the SRC and sent to the SRS. Different snapshots of MS objects may be sent whenever there is a change in media (e.g., a direction change, like pause/resume, codec change, and/or participant change). The MS object is represented in the XML schema using the 'stream' element.6.7.1. Attributes
A MS class has the following attributes: o label - The 'label' attribute within the 'stream' XML element references an SDP "a=label" attribute that identifies an m-line within the RS SDP. That m-line carries the media stream from the SRC to the SRS. o content-type - The content of a MS element will be described in terms of the "a=content" attribute defined in Section 5 of [RFC4796]. If the SRC wishes to convey the content-type to the SRS, it does so by including an "a=content" attribute with the m-line in the RS SDP.
o stream_id - Each 'stream' element has a unique 'stream_id'
attribute that helps to uniquely identify the stream. This
identifier is generated using the rules mentioned in Section 6.10.
o session_id - This attribute associates the stream with a specific
'session' element.
The metadata model can include media streams that are not being
delivered to the SRS. For example, an SRC offers audio and video
towards an SRS that accepts only audio in response. The metadata
snapshots sent from the SRC to the SRS can continue to indicate the
changes to the video stream as well.
6.7.2. Linkages
A MS class is linked to the participant and CS classes by using the
association relationship. Details regarding associations with the
participant are described in Section 6.5. Details regarding
associations with the CS are mentioned in Section 6.3.
6.8. Participant-Stream Association
+-------------------------+
| Participant-Stream |
| Association |
+-------------------------+ +-----------Participant
| associate-time | | 0..* | 1..* |
| disassociate-time |---+ receives| |sends
| send | | 0..* | 0..* |
| recv | | | |
| participant_id | | | |
+-------------------------+ | | |
+-----------Media Stream
A Participant-Stream Association class describes the association of a
participant to a MS for a period of time, as a sender or as a
receiver, or both.
This class is represented in XML using the 'participantstreamassoc'
element.
6.8.1. Attributes
A Participant-Stream Association class has the following attributes: o associate-time - This attribute indicates the time a participant started contributing to a MS. o disassociate-time - This attribute indicates the time a participant stopped contributing to a MS. o send - This attribute indicates whether a participant is contributing to a stream or not. This attribute has a value that points to a stream represented by its unique_id. The presence of this attribute indicates that a participant is contributing to a stream. If a participant stops contributing to a stream due to changes in a CS, a snapshot MUST be sent from the SRC to the SRS with no 'send' element for that stream. o recv - This attribute indicates whether a participant is receiving a media stream or not. This attribute has a value that points to a stream represented by its unique_id. The presence of this attribute indicates that a participant is receiving a stream. If the participant stops receiving a stream due to changes in a CS (like hold), a snapshot MUST be sent from the SRC to the SRS with no 'recv' element for that stream. o participant_id - This attribute points to the participant with which a 'stream' element is associated. The 'participantstreamassoc' XML element is used to represent a participant association with a stream. The 'send' and 'recv' XML elements MUST be used to indicate whether a participant is contributing to a stream or receiving a stream. There MAY be multiple instances of the 'send' and 'recv' XML elements inside a 'participantstreamassoc' element. If a metadata snapshot is sent with a 'participantstreamassoc' element that does not have any 'send' and 'recv' elements, it means that the participant is neither contributing to any streams nor receiving any streams.6.8.2. Linkages
The Participant-Stream Association class is linked to the participant and MS classes.
6.9. Syntax of XML Elements for Date and Time
The XML elements 'associate-time', 'disassociate-time', 'start-time', and 'stop-time' contain strings representing the date and time. The value of these elements MUST follow the Instant Messaging and Presence Protocol (IMPP) date-time format [RFC3339]. Timestamps that contain "T" or "Z" MUST use the capitalized forms. As a security measure, the 'timestamp' element MUST be included in all tuples, unless the exact time of the status change cannot be determined.6.10. Format of Unique ID
A unique_id is generated in two steps: o The Universally Unique Identifier (UUID) is created using any of the procedures mentioned in Sections 4.3, 4.4, and 4.5 of [RFC4122]. The algorithm MUST ensure that it does not use any potentially personally identifying information to generate the UUIDs. If implementations are using a Name-Based UUID as defined in Section 4.3 of [RFC4122], a namespace ID generated using the guidance in Section 4.2 or 4.5 of [RFC4122] might be a good choice. o The UUID is encoded using base64 as defined in [RFC4648]. The above-mentioned unique_id mechanism SHOULD be used for each metadata element. Multiple SRCs can refer to the same element/UUID (how each SRC learns the UUID here is beyond the scope of this document). If two SRCs use the same UUID, they MUST retain the UUID/element mapping. If the SRS detects that a UUID is mapped to more than one element at any point in time, it MUST treat this as an error. For example, the SRS may choose to reject or ignore the portions of metadata where it detects that the same UUID is mapped to an element that is different than the expected element (the SRS learns the mapped UUID when it sees an element for the first time in a metadata instance).6.11. Metadata Version Indicator
The Metadata version is defined to help the SRC and SRS know the version of metadata XML schema used. SRCs and SRSs that support this specification MUST use version 1 in the namespace (urn:ietf:params:xml:ns:recording:1) in all the XML documents. Implementations may not interoperate if the version implemented by the sender is not known by the receiver. No negotiation of versions is provided. The version number has no significance, although
documents that update or obsolete this document (possibly including drafts of such documents) should include a higher version number if the metadata XML schema changes.
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