Network Working Group A. Knauf Internet-Draft G. Hege Intended status: Standards Track T C. Schmidt Expires: November 9, 2012 HAW Hamburg M. Waehlisch link-lab & FU Berlin May 8, 2012 A RELOAD Usage for Distributed Conference Control (DisCo) draft-knauf-p2psip-disco-05 Abstract This document defines a RELOAD Usage for Distributed Conference Control (DisCo) with SIP. DisCo preserves conference addressing through a single SIP URI by splitting its semantic of identifier and locator using a new Kind data structure. Conference members are enabled to select conference controllers based on proximity awareness and to recover from failures of individual resource instances. DisCo proposes call delegation to balance the load at focus peers. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 9, 2012. Copyright Notice Copyright (c) 2012 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 Knauf, et al. Expires November 9, 2012 [Page 1] Internet-Draft DisCo May 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview of DisCo . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Reference Scenario . . . . . . . . . . . . . . . . . . . . 6 3.2. Initiating a Distributed Conference . . . . . . . . . . . 7 3.3. Joining a Conference . . . . . . . . . . . . . . . . . . . 8 3.4. Conference State Synchronization . . . . . . . . . . . . . 9 3.5. Call delegation . . . . . . . . . . . . . . . . . . . . . 10 3.6. Resilience . . . . . . . . . . . . . . . . . . . . . . . . 10 3.7. Topology Awareness . . . . . . . . . . . . . . . . . . . . 10 4. RELOAD Usage for Distributed Conference Control . . . . . . . 11 4.1. Shared Resource DisCo-Registration . . . . . . . . . . . . 11 4.2. Kind Data Structure . . . . . . . . . . . . . . . . . . . 11 4.3. Variable Conference Identifier . . . . . . . . . . . . . . 12 4.4. Conference Creation . . . . . . . . . . . . . . . . . . . 12 4.5. Advertising Focus Ability . . . . . . . . . . . . . . . . 13 4.6. Determining Coordinates . . . . . . . . . . . . . . . . . 14 4.7. Proximity-aware Conference Participation . . . . . . . . . 14 4.8. Configuration Document Extension . . . . . . . . . . . . . 16 5. Conference State Synchronization . . . . . . . . . . . . . . . 18 5.1. Event Package Overview . . . . . . . . . . . . . . . . . . 18 5.2. . . . . . . . . . . . . . . . . . 20 5.3. / . . . . . . . . . . . . . . . . 20 5.4. . . . . . . . . . . . . . . . . . 21 5.5. . . . . . . . . . . . . . . . . . . . . . . . . . 22 5.5.1. . . . . . . . . . . . . . . . . . . . . 23 5.5.2. / . . . . . . . . . . . . . . . . . . . . 23 5.5.3. / . . . . . . . . . . . . . . . . 24 5.6. Distribution of Change Events . . . . . . . . . . . . . . 24 5.7. Translation to Conference-Info Event Package . . . . . . . 25 5.7.1. . . . . . . . . . . . . . . . . . . 26 5.7.2. . . . . . . . . . . . . . . . 26 5.7.3. . . . . . . . . . . . . . . . . . . . . . 26 5.7.4. . . . . . . . . . . . . . . . . . . 26 5.7.5. / . . . . . . . . . . . . . . . . . . . . 27 5.7.6. / . . . . . . . . 27 6. Distributed Conference Control with SIP . . . . . . . . . . . 28 6.1. Call delegation . . . . . . . . . . . . . . . . . . . . . 28 6.2. Conference Access . . . . . . . . . . . . . . . . . . . . 29 Knauf, et al. Expires November 9, 2012 [Page 2] Internet-Draft DisCo May 2012 6.3. Media Negotiation and Distribution . . . . . . . . . . . . 30 6.3.1. Offer/Answer . . . . . . . . . . . . . . . . . . . . . 30 6.3.2. New Peers Joining . . . . . . . . . . . . . . . . . . 31 6.4. Restructuring a Conference . . . . . . . . . . . . . . . . 31 6.4.1. On Graceful Leave . . . . . . . . . . . . . . . . . . 31 6.4.2. On Unexpected Leave . . . . . . . . . . . . . . . . . 32 7. DisCo Kind Definition . . . . . . . . . . . . . . . . . . . . 33 8. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 34 9. Relax NG Grammar . . . . . . . . . . . . . . . . . . . . . . . 38 10. Security Considerations . . . . . . . . . . . . . . . . . . . 39 10.1. Trust Aspects . . . . . . . . . . . . . . . . . . . . . . 39 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 41 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 42 13.1. Normative References . . . . . . . . . . . . . . . . . . . 42 13.2. Informative References . . . . . . . . . . . . . . . . . . 43 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 44 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46 Knauf, et al. Expires November 9, 2012 [Page 3] Internet-Draft DisCo May 2012 1. Introduction This document describes a RELOAD Usage for distributed conference control (DisCo) in a tightly coupled model with SIP [RFC3261]. The Usage provides self-organizing and scalable signaling that allows RELOAD peers, clients and plain SIP user agents to participate in a managed P2P conference. DisCo defines the following functions: o A SIP protocol scheme for distributed conference control o RELOAD Usage and definition of conferencing Kind o Mechanisms for conference synchronization and call delegation o Mechanism for proximity-aware routing within a conference o An XML event package for distributed conferences In this document, the term distributed conferencing refers to a multiparty conversation in a tightly coupled model in which the point of control (i.e., the focus) is identified by a unique URI, but the focus service is located at many independent entities. Multiple SIP [RFC3261] user agents uniformly control and manage a multiparty session. This document defines a new Usage for RELOAD, including an additional Kind code point with a corresponding data structure that complies with the demands for distributed conferences. The 'DisCo' data structure stores the mapping of a single conference URI to multiple conference controllers and thereby separates the conference identifier from focus instantiations. Authorized controllers of a conference are permitted to register their mapping in the DisCo data structure autonomously. Thus, the DisCo data structure represents a co-managed Resource in RELOAD. To provide trusted and secure access to a co-managed Resource, this document uses the definitions for Shared Resources (ShaRe) [I-D.knauf-p2psip-share]. Delay and jitter are critical issues in multimedia communications. The proposed conferencing scheme supports mechanisms to build an optimized interconnecting graph between conference participants and their responsible conference controllers. Conference members will be enabled to select the closest focus with respect to delay or jitter. DisCo extends conference control mechanisms to provide a consistent and reliable conferencing environment. Controlling peers maintain a consistent view of the entire conference state. The multiparty system can be re-structured based on call delegation operations. Knauf, et al. Expires November 9, 2012 [Page 4] Internet-Draft DisCo May 2012 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]. We use the terminology and definitions from der RELOAD base draft[I-D.ietf-p2psip-base], the peer-to-peer SIP concepts draft [I-D.ietf-p2psip-concepts], the usage for shared resources draft [I-D.knauf-p2psip-share],and the terminology formed by the framework for conferencing with SIP [RFC4353]. Additionally the following terms are used: Coordinate Value: An opaque string that describes a host's relative position in the network topology. Focus peer: A RELOAD peer that provides SIP conferencing functions and implements the Usage for distributed conferencing. It is called 'active' if already involved in signaling relation to conference participants. Otherwise, if only registered in a distributed conference data structure, it is referred to as a 'potential' focus peer. Knauf, et al. Expires November 9, 2012 [Page 5] Internet-Draft DisCo May 2012 3. Overview of DisCo 3.1. Reference Scenario The reference scenario for the Distributed Conference Control (DisCo) is shown in Figure 1. Peers are connected via a RELOAD [I-D.ietf-p2psip-base] instance, in which peers A and B are managing a single multiparty conference. The conference is identified by a unique conference URI, but located at peers A and B fulfilling the role of the focus. The mapping of the conference URI to one or more responsible focus peers is stored in a new RELOAD Resource for distributed conferencing within a data structure denoted as DisCo- Registration. The storing peer SP of the distributed conference resource holds this data. The focus peers A and B maintain SIP signaling relations to conference participants, which may have different conference protocol capabilities. In this example, peer A is the focus for the RELOAD peer C and the plain SIP user agent E whereas peer B serves as a focus for RELOAD peer D and the RELOAD client F. RELOAD peers and clients obtain the contact information for the conference from the storing peer. In contrast to this, the user agent E receives the conference URI not by RELOAD mechanisms, but resolves the ID and joins the conference by plain SIP negotiation. Focus peers maintain a SIP signaling relation among each other used for notification messages that synchronize the conference focus peers' knowledge about the entire conference state. Additionally, focus peers can transfer calls to each other by a call delegation mechanism. Knauf, et al. Expires November 9, 2012 [Page 6] Internet-Draft DisCo May 2012 +-------------------+ +------------------+ |Access Control List| |DisCo-Registration| +-------------------+ +------------------+ \ / +-------+ |Storing| # # # # # # # # # # | Peer | # # # # # # # # # # # | SP | # # +-------+ # # # # # # # +----+ +----+ |Peer| \ RELOAD Instance |Peer| | C | \ | D | +----+ \ +----+ # SIP # # \ # # \ # # +-------+ +-------+ #( # | Focus | | Focus | # ) # # | Peer | # # # # # # # # # # # | Peer | # # ( | A | <===Conf.Events/====> | B | ) +-------+ Call delegation +-------+ Overlay / \ Comm. / \ ( SIP SIP ) / \ ( / \ ) +----------+ +--------+ |User Agent| | Client | | E | | F | +----------+ +--------+ Figure 1: Reference Scenario: Focus peers A,B maintain a distributed conference 3.2. Initiating a Distributed Conference To create a conference the initiating user agent announces itself as a focus for the conference. It stores its own contact information (Node-ID) as a DisCo-Registration Kind (cf. Figure 2) in the RELOAD overlay. The hashed conference URI is used as the Resource-ID. This Resource will later contain the contact IDs of all potential focus peers including optional topological descriptors. Knauf, et al. Expires November 9, 2012 [Page 7] Internet-Draft DisCo May 2012 3.3. Joining a Conference A RELOAD-aware node (cf. Bob in Figure 2) intending to join an existing conference requests the list of potential focus peers stored in the DisCo-Registration under the conference's Resource-ID. The node selects any of the focus peers (e.g., Alice) and establishes a connection using AppAttach/ICE [RFC5245]. This transport is then used to send an INVITE to the conference applying the chosen focus as the contact. The selection of the focus peer can optionally be based on proximity information if available. A conference member proposes itself as a focus for subsequent participants by adding its Node-ID to the DisCo-Registration stored under the conference URI in the RELOAD overlay. The decision whether a peer announces as a focus incorporates bandwidth, power, and other constraints, but details are beyond the scope of this document. Knauf, et al. Expires November 9, 2012 [Page 8] Internet-Draft DisCo May 2012 Alice RELOAD Bob (initiating peer) (joining peer) -------------------------------------------------------------------- | | | | Alice stores her mapping to register a conference | | Store mapping(ConfURI, Alice) | | |------------------------------>| | | Bob requests the list of potential focus peers | | | Lookup ConfURI | | |<------------------------------| | | Result list of conf. focus | | |------------------------------>| | | | | Bob establishes transport connection to Alice | | AppAttach | |<--------------------------------------------------------------| | AppAttach | |-------------------------------------------------------------->| | INVITE | |<~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| | OK | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>| | ACK | |<~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| | Media | |<=============================================================>| | | | | Bob stores his mapping to become a focus peer too | | | Store mapping(ConfURI, Bob) | | |<------------------------------| | | | Figure 2: DisCo Usage generic Call Flow 3.4. Conference State Synchronization Each focus of a conference maintains signaling connections to its related participants independently from other conference controllers. This distributed conference design effects that the entire SIP conference state is jointly held by all focus peers. In DisCo, state synchronization is based on a SIP specific event notifications mechanism [RFC3265]. Each focus peer maintains its view of the entire conference state by subscribing to the other focus peers' XML event package for distributed conferences. This is based on the event package for conference state (cf. [RFC4575]). Details are defined in this document in Section 5. Receivers of event notifications update their Knauf, et al. Expires November 9, 2012 [Page 9] Internet-Draft DisCo May 2012 local conference state document to represent a valid view of current total conference state. The event notification package for distributed conferences enables focus peers to synchronize the entire conference state. The event package defines additional XML elements and complex types (see Section 8 for more details), which describe the responsibilities of any focus peer in the conference. By providing a global view each focus peer is enabled to perform additional load balancing operations and enhances the robustness against departures of focus peers. 3.5. Call delegation Call delegation (see Section 6.1) is a feature used to transfer an incoming participation request to another focus peer. It can be applied to prevent overloading of focus peers. Call delegation is realized through SIP REFER requests, which carry signaling and session description information of the caller to be transferred. This feature is achieved transparently for the transferred user agent by using a source routing mechanism at SIP dialog establishment. Descriptions of overload detection are beyond the scope of this document. 3.6. Resilience A focus peer can decide to leave the conference or may ungracefully fail. In a traditional conferencing scenario, loss of the conference controller or the media distributor would cause a complete failure of the multiparty conversation. Distributed conferencing uses the redundancy provided by multiple focus peers to reconfigure a current multiparty conversation. Participants that loose their entry point to the conference re-invite themselves via the remaining focus peers or will be re-invited by the latter. This option is based on the conference state and call delegation functions. 3.7. Topology Awareness DisCo supports the optimization of the conference topology in respect of the underlying network using topological descriptors. An extension for the RELOAD XML configuration document is defined in Section 4.8 to support landmarking approaches. Each peer intending to create or participate in a distributed conference MAY determine a topological descriptor that describes its relative position in the network. Focus peers store these coordinate values in an additional data field in the DisCo-Registration data structure. This enables peers joining the conference to select the closest focus with respect to its coordinate values. Knauf, et al. Expires November 9, 2012 [Page 10] Internet-Draft DisCo May 2012 4. RELOAD Usage for Distributed Conference Control 4.1. Shared Resource DisCo-Registration A distributed conference is a cooperative service of several individual devices that use a common identifier. To enable a mapping from one conference identifier to multiple focus peers, this document defines the new Kind data structure DisCo-Registration. The DisCo Kind uses the definitions for Shared Resources [I-D.knauf-p2psip-share] to allow a jointly maintenance by multiple focus peers. Hence, write permission to a DisCo-registration is shared by the conference creator with all authorized focus peers. DisCo complies with the following requirements for Shared Resources: Isolated Data Storage: DisCo uses the dictionary data model. Each dictionary key is the Node-ID of the certificate that will be used to sign the stored data ResourceNameExtension field: A DisCo-Registration can contain the ResourceNameExtension structure an initial field in the Kind data structure. It contains the conference URI of the registered DisCo-record. 4.2. Kind Data Structure Each DisCo-Registration data structure stores a mapping of a conference identifier to one or multiple focus peers that cooperatively control the conference. Additionally, each DisCo- Registration provides the coordinate value, which indicates the relative network position of the focus peers. The data structure uses the RELOAD dictionary type. The dictionary key MUST be the Node-ID of the focus peer that is associated with the dictionary entry. This allows a focus peer to update only its own mapping. The DisCo data structure of type DisCoRegistration is constructed as follows: struct { /* This field is optional, see documentation */ ResourceNameExtension res_name_ext; opaque coordinate<0..2^16-1>; NodeId node_id; } DisCoRegistration; The DisCoRegistration structure is composed of the following values: Knauf, et al. Expires November 9, 2012 [Page 11] Internet-Draft DisCo May 2012 res_name_ext: This field can contain the conference URI. It meets the requirement for the USER-CHAIN-ACL access policy defined in [I-D.knauf-p2psip-share] to enable variable resource names. coordinate: This field contains a topological descriptor that indicates the relative position of the peer in the network. To support different algorithms the coordinate field is represented as an opaque string. node_id: This field contains the Node-ID of the peer storing the DisCoRegistration and is used to contact the peer when utilizing its service as a focus. 4.3. Variable Conference Identifier DisCo-Registrations can be stored based on a variable Resource Name. However, a conference identifier set by a user MUST follow the requirements for Kinds using variable Resource Names as defined in the ShaRe Usage [I-D.knauf-p2psip-share]. 4.4. Conference Creation The registration of a distributed conference includes the storage of the following two Kinds (see Figure 3). DisCo-Registration Kind: contains the conference identifier and the optional coordinate value. If used, the coordinate value MAY be determined previously to the conference registration. The Resource Name and hence the Resource-ID is defined by the hash over the desired conference identifier (using the hash algorithm of the overlay). Access Control List Kind: contains the conference participants that are allowed to register as focus peers for a conference (see [I-D.knauf-p2psip-share]). Its Resource Name/ID is equal to those of the corresponding DisCo-Registration. Preliminary to storage of DisCo-Registration and Access Control List (ACL) Kinds the conference creator SHOULD perform a RELOAD StatReq to verify that no former conference is present. If neither a DisCo- Registration nor an associated ACL exist, the conference creator stores a DisCo-Registration with a valid conference identifier (see Section 4.3) and an ACL referring to the DisCo-Registration Kind-ID. If DisCo registrations and ACL Kinds from previous conferences are still existing there are two options. First, if conference creator is aware of the indexes from previous ACL Kinds, it refreshes the root item of this ACL and stores its registration as focus peer as Knauf, et al. Expires November 9, 2012 [Page 12] Internet-Draft DisCo May 2012 DisCo-Registration Kind. Second, If the creator is unaware of indexes, it fetches all Access List Kinds to determine the index of the root item. Alice Peer1 Overlay PeerN Storing Peer ------------------------------------------------------------- | StatReq Res:Conf-URI | | |------------>|----------->|----------->|----------->| | StatAns | | | |<------------|<-----------|<-----------|<-----------| | StoreReq Res:Conf-URI Kinds:DisCo, Access-List | |------------>|----------->|----------->|----------->| | StoreAns | | | |<------------|<-----------|<-----------|<-----------| | | | | | Figure 3: Initial creation of a Distributed Conference Optionally the conference initiator (or any active focus) MAY store an additional RELOAD SIP-Registration in the overlay [I-D.ietf-p2psip-sip] or even at a standard SIP registrar [RFC3261] under a URI for which it has write permission. This allows DisCo- unaware or even legacy SIP user agents to participate in the conference. Those registrations SHOULD always point to a currently active focus, who is prepared to accept legacy user agents. The user agent who initially performed the registrations is responsible for updating them appropriately. How authorization has been obtained to perform those registration is out of scope of this document. The lifetime of a distributed conference is not necessarily limited by the participation time of its creator. As long as the root item of an Access Control List to a DisCo-Registration is not expired, Authorized Peers are allowed to further provide a conferencing service and even store new focus registrations. 4.5. Advertising Focus Ability All participants of a distributed conference MAY potentially become a focus peer for their conference. This depends on its capacities such as sufficient processing power (CPU, Memory) for the desired media type, the quality of the network connectivity, and the conference policy. Information about network connectivity with respect to NAT or restricted firewalls can be obtained via ICE [RFC5245] connectivity checks. If a peer is behind a NAT, it SHOULD allow for incoming connections via AppAttach/ICE. Peers that can only accept connections with the support of TURN should not act as a focus. Knauf, et al. Expires November 9, 2012 [Page 13] Internet-Draft DisCo May 2012 Nevertheless, under special circumstances it might be reasonable to locate a focus peer behind such a NAT (e.g., within a companies network infrastructure). If a participant is a candidate to become a focus for the conference, it stores its Node-ID and optional coordinate value into the DisCo data structure. An entry in the corresponding ACL [I-D.knauf-p2psip-share] must be present to allow this peer to write the DisCo-Registration resource. By storing the mapping into the data structure a participant becomes a potential focus. 4.6. Determining Coordinates Each RELOAD peer within the context of a distributed conference MAY be aware of its relative position in the network topology. To constuct a topology-aware conference, the DisCo Usage provides the coordinate value within the DisCo-Registration data structure. Focus peers store their relative network position together with the announcement as conference focus. Joining peers that are able to determine their coordinates may then select a focus peer whose relative position is in its vicinity (see Section 4.7). Some algorithms determine topology information by measuring Round- Trip Times (RTT) towards a set of hosts serving as landmarks (e.g., [landmarks-infocomm02]). To support such algorithms this document describes an extension to the RELOAD XML configuration document that allows to configure the set of landmark hosts peer must use for position estimation (see Section 4.8). Once a focus peer has registered its mapping in the DisCo data structure, it also stores the according coordinates in the same mapping. These vectors are used by peers joining the conference to select the focus peer that is relatively closest to itself. Because topology-awareness can be obtained by many different approaches a concrete algorithms is out of scope of this document. 4.7. Proximity-aware Conference Participation The participation procedure to a distributed conference is composed of three operation. 1. Resolution of the conference identifier. 2. Establishment of of transport connection. 3. SIP signaling to join a conference. Figure 4 and the following specifications give a more detailed view Knauf, et al. Expires November 9, 2012 [Page 14] Internet-Draft DisCo May 2012 on the joining procedure. Bob Peer1 Overlay PeerN Storing Peer Alice -------------------------------------------------------------- | StatReq Res:Conf-URI | | | |--------->|--------->|--------->|--------->| | | |StatAns | | | | |<---------|<---------|<---------|<---------| | | FetchReq Res:Conf-URI Kind:DisCo,ACL | | |--------->|--------->|--------->|--------->| | | |FetchAns | | | | |<---------|<---------|<---------|<---------| | | | | | | | | Bob calculates Alice as closest Focus | | | | | | | | | |AppAttach application:5060 | | |--------->|--------->|--------->|--------->|--------->| | |AppAttach application:5060 | | |<---------|<---------|<---------|<---------|<---------| | | | | | | |<-------------------ICE Checks----------------------->| | | | | | | | | INVITE sip:Alice | | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>| | | 200 OK | | | |<~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| | | ACK | | | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>| | | | | | | Figure 4: Participation of a Distributed Conference 1. The joining peer MAY determine its own coordinate value (if used). 2. The joining peer sends a StatReq message to obtain all indexes of the Access Control List (ACL) Kinds stored. 3. The joining peer sends a FetchReq message for the DisCo and ACL Kind to the Resource-ID of the conference URI. The FetchReq SHOULD NOT include any specific dictionary keys, but SHOULD fetch for those array ranges previously determined the StatReq. With the ACL items, the joining peer is able to verify whether DisCo- Registrations are stored by authorized focus peers (see [I-D.knauf-p2psip-share]). 4. Using the retrieved coordinates values of the DisCo- Registrations, the joining peer MAY calculate which of than Knauf, et al. Expires November 9, 2012 [Page 15] Internet-Draft DisCo May 2012 opaque <0..2^16-1> initial field in the Kind data structure focus peers is the relatively closest to itself. 5. The joining peer then establishes a transport using RELOADs AppAttach, respectively, ICE procedures to create a transport to the chosen focus peer. 6. Finally, the established transport is used to create a SIP dialog from the joining peer to the focus peers. The SIP INVITE request MAY contain the joining peer's topological descriptor as a URI-parameter called 'coord' in the contact-header in base64 encoded form [RFC4648]. An example contact URI is "sip:alice@ example.com;coord=PEknbSBhIHRvcG9sb2dpY2FsIGRlc2NyaXB0b3I+". When the called focus is full and needs to delegate the call it uses the contents of the 'coord'-parameter. It determines the next available focus closest to the calling peer (Section 4.6) using the received descriptor and the other focuses' descriptors from the conference state synchronization document and delegates the call accordingly (see Section 6.1). A conference focus MAY allow the joining peer to also become a focus (depending on the conference policy see Section 6.2). Therefore, it stores a new ACL Kind that delegates write permission for the DisCo- Registration to the new participant. It sets the 'user_name' field in the ACL Kind to its own user name and sets the 'to_user' field to the user name of the joining peer. If no other conference policy is defined, the focus peer MAY set the allow_delegation flag to true. For further details about the trust delegation using the ACL Kind see [I-D.knauf-p2psip-share]. 4.8. Configuration Document Extension This section defines an additional parameter for the element that extends the RELOAD XML configuration document. The proposed element allows RELOAD provider to publish a set of accessible and reliable hosts that SHOULD be used if RELOAD peers use landmarking algorithms to determine relative position in the network topology. The element serves as container for the sub-elements, each representing a single host that serves as a landmark. The uses the following attributes: address: The IP address (IPv4 or IPv6) of the landmark host. Knauf, et al. Expires November 9, 2012 [Page 16] Internet-Draft DisCo May 2012 port: The port on which the landmark host responds for distance estimation. More than one landmark hosts SHOULD be present in the configuration document. Knauf, et al. Expires November 9, 2012 [Page 17] Internet-Draft DisCo May 2012 5. Conference State Synchronization The global knowledge about signaling and media relations among the conference participants and focus peers defines the global state of a distributed conference. It is composed of the union of every local state at the focus peers. To enable focus peers to provide conference control operations that modify and/or require the global state of a conference, this document defines a mechanism for inter- focus state synchronization. It is based on mutual subscriptions for an Event Package for Distributed Conferences and allows to preserve a coherent knowledge of the global conference state. This XML based event package named 'distributed-conference' MUST be supported by each RELOAD peer that is registered with a DisCo-Registration. Participants of a distributed conference MAY support it. To provide backward compatibility to conference members that do not support the distributed-conference event package, this document defines a translation to the Event Package for Conference State [RFC4575]. 5.1. Event Package Overview The 'distributed-conference' event package is designed to convey information about roles and relations of the conference participants. Conference controllers obtain the global state of the conference and use this information for load balancing or conference restructuring mechanisms in case of a focus failure. Figure Figure 5 gives a general overview of the document hierarchy. Knauf, et al. Expires November 9, 2012 [Page 18] Internet-Draft DisCo May 2012 distributed-conference | |-- version-vector | |-- version | |-- version | |-- conference-description | |-- focus | |-- focus-state | | |-- user-count | | |-- coordinate | | |-- maximum-user-count | | |-- active | | |-- locked | | |-- conf-uris | | |-- available-media | | | |-- users | | |-- user | | | |-- endpoint | | | | |-- media | | | | |-- call-info | | | |-- relations | | |-- relation |-- focus | |-- ... Figure 5: Overview of the event package for distributed conferences The document structure is designed to allow concurrent change events at several focus peers. To prevent race conditions each focus peer has exclusive writing permission to the 'focus' sub element that describes itself. It is achieved by a unique mapping from a focus peer to its XML element using the 'Element Keys' mechanisms for partial notification [RFC4575](sections 4.4-5.). A focus peer is only allowed to update or change that sub element, whose 'entity' Element Key contains its RELOAD user name. This restriction also applies to the child elements of the 'version-vector' element. Each 'version' number belongs to a specific focus peer maintaining the version number. The local state of a focus peer is described within a 'focus' element. It provides general information about a focus peer and its signaling and media relations to participants and focus peers. The Conference participants are aggregated within 'users' elements, respectively, 'user' sub elements. Knauf, et al. Expires November 9, 2012 [Page 19] Internet-Draft DisCo May 2012 General information about the conference as a whole, is provided within a 'conference-description' element. In contrast to the 'focus' and 'version-vector' elements, conference description is not meant for concurrent updating. Instead, it provides static conference descriptions that rarely change during a multiparty session. More detailed descriptions about the event package and its elements are provided in the following sections. The complete XML schema definition is given in Section 8. 5.2. The element is the root of a distributed conference XML document. It uses the following attributes: entity: This attribute contains the conference URI that identifies the distributed conference. A SIP SUBSCRIBE request addressed to this URI initiates an subscribe/notify relation between participants and their related focus peer. state: This attribute indicates whether the content of a distributed conference document is a 'full', 'partial' or 'deleted' information. It is in accordance with [RFC4575] to enable the partial notification mechanism. The child elements are , and the elements. An event notification of state 'full' MUST include all these elements. An event notification of state 'partial' MUST contain at least and its sub elements. 5.3. / The Event Package for Distributed Conferences uses the and its sub elements to enable a coherent versioning scheme. It is based on vector clocks as defined in [timestamps-acsc88]. Each element contains a unsigned integer that describes the state of a specific focus peer and contains the following attributes: entity: This attribute contains the user name of the focus peer whose local version number is described by this element. node-id: This attribute contains the Node-ID of the focus peer. Whenever the local status of a focus peer changes (e.g. a new participant arrived) the version number of the corresponding Knauf, et al. Expires November 9, 2012 [Page 20] Internet-Draft DisCo May 2012 element MUST be incremented by one. Each change in the local state also triggers a new event notification containing the entire and the changes contained in a element. The recipient of a change event needs to update it local XML document. If a received number is higher that the local, it updates the element and its associated element with the retrieved elements. All other elements remain constant. If the length or contents of the retrieved is different to the local copy it indicates a incoherent knowledge about the entire conference state. If the retrieved contains any unknown focus peers and any local version numbers for the known focus peers is lower, the receiver SHOULD request a 'full' XML notification. If any local number is retarded more than one, the receiver SHOULD request a 'full' event notification from the sender. The full state notification updates all elements whose corresponding element is out of date. 5.4. The element provides general information and links to auxiliary services for the conference. The following sub elements provide human-readable text descriptions about the conference: : Contains a short textual description about the conference : Contains the subject of the conference : Contains a longer textual description about the conference : Contains a list of keywords that match the conference topic. The XML schema definition and semantic is imported from the 'conference-info' event package [RFC4575]. The sub element enables focus peers to advertise auxiliary services for the conference. The XML schema definition and semantic is imported from the 'conference-info' event package [RFC4575]. The element uses the 'state' Element Key to enable the partial notification mechanism. Knauf, et al. Expires November 9, 2012 [Page 21] Internet-Draft DisCo May 2012 5.5. Each element describes a focus peer actively controlling the conference. It provides general information about a focus peer (e.g., display-text, languages, etc.), contains conference specific information about the state of a focus peer (user-count, available media types, etc.) and announces signaling and media information about the maintained participants. Additionally, it describes signaling or media relations to further focus peers. The element uses the following attributes: entity: This attribute contains the user name of the RELOAD peer acting as focus peer. It uniquely identifies the focus peer that is allowed to update or change all sub elements of . All other focus peers SHOULD NOT update or change sub elements of this element. A SUBSCRIBE request addressed to the user name initiates a conference state synchronization with the focus peer. Node-ID This attributed contains the Node-ID of the peer acting as conference focus state: In accordance to [RFC4575], this attribute indicates whether the content of the element is a 'full', 'partial' or 'deleted' information. A 'partial' notification contains at maximum a single element. The following sub elements of provide general information about a focus peer: : Contains a short text description of the user acting as focus peer. : This element contains additional URIs that are associated with this user. This element MAY contain human-readable text descriptions about the roles of the user in the conference. : This element contains a list of tokens, each describing a language understood by the user. The XML schema definition and semantic for , and are imported from the 'conference-info' event package [RFC4575] Following, a detailed description of the remaining sub elements. Knauf, et al. Expires November 9, 2012 [Page 22] Internet-Draft DisCo May 2012 5.5.1. The element aggregates a set of conference specific information about the RELOAD user acting as focus peer. The following attribute is defined for the element: status: This attribute indicates whether the content of the element is a 'full', 'partial' or 'deleted' information. The element has the following sub elements: : This element contains the number of participants that are connected to the conference via this focus peer at a certain moment. This element contains the coordinate value Section 4.2 of the focus peer : This number indicates a threshold of participants a focus peer is able to serve. This value might change during a conference, depending on the focus peers current load. : This element MAY contain other conference URIs in order to access the conference via different signaling means. The XML schema definition and semantic is imported from [RFC4575]. : This element is imports the type XML scheme definitions from [RFC4575]. It allows a focus peer to list its available media streams. : This boolean element indicates whether a focus peer is currently active. Conference participation requests or a call delegation request SHOULD succeed. : In contrast to , this element indicates that a focus peer is not willing to accept anymore participation or call delegation request. 5.5.2. / The , respectively, each element describes a single participant that is maintained by the focus peer described by the parent element. The element XML schema definition and its semantic is imported from the 'conference-info' event package [RFC4575]. Knauf, et al. Expires November 9, 2012 [Page 23] Internet-Draft DisCo May 2012 5.5.3. / The element serves as container for elements, each describing a specific connection to another focus peer. The parent element uses the 'state' attribute to enable the partial notification mechanism. For the element the following attributes are defined: entity: This attribute contains the user name of the remote focus. node-id This attribute contains the Node-ID of the remote focus peer. The content of each is a comma separated string that describes the tuple . The CONNECTION- TYPE is a string token describing the type of connection (e.g. media, signaling, etc.) and the IDENTIFIER contains a variable connection identifier. It is a generic method to announce any kind of connection to a remote focus. This specification defines following tuples: media: