MediaCtrl T. Melanchuk, Ed. Internet-Draft Rain Willow Communications Expires: April 7, 2008 October 5, 2007 An Architectural Framework for Media Server Control draft-ietf-mediactrl-architecture-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 7, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Melanchuk Expires April 7, 2008 [Page 1] Internet-Draft Mediactrl Architecture October 2007 Abstract This document describes an Architectural Framework for Media Server Control. The primary focus will be to define logical entities that exist within the context of the MediaCtrl Work Group in the IETF. This document will also define appropriate naming conventions and interactions between the core logical entities. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Architecture Overview . . . . . . . . . . . . . . . . . . . . 7 5. SIP Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Media Control for IVR Services . . . . . . . . . . . . . . . . 14 6.1. Basic IVR Services . . . . . . . . . . . . . . . . . . . . 15 6.2. IVR Services with Mid-call Controls . . . . . . . . . . . 15 6.3. Advanced IVR Services . . . . . . . . . . . . . . . . . . 15 7. Media Control for Conferencing Services . . . . . . . . . . . 16 7.1. Creating a New Conference . . . . . . . . . . . . . . . . 18 7.2. Adding a Participant To a Conference . . . . . . . . . . . 18 7.3. Media Controls . . . . . . . . . . . . . . . . . . . . . . 19 7.4. Floor Control . . . . . . . . . . . . . . . . . . . . . . 19 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 25 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27 11.1. Normative References . . . . . . . . . . . . . . . . . . . 27 11.2. Informative References . . . . . . . . . . . . . . . . . . 27 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 29 Intellectual Property and Copyright Statements . . . . . . . . . . 30 Melanchuk Expires April 7, 2008 [Page 2] Internet-Draft Mediactrl Architecture October 2007 1. Introduction To be completed. Melanchuk Expires April 7, 2008 [Page 3] Internet-Draft Mediactrl Architecture October 2007 2. Conventions In this document, BCP 14/RFC 2119 [1] defines the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL". In addition, BCP 15 indicates requirement levels for compliant implementations. Melanchuk Expires April 7, 2008 [Page 4] Internet-Draft Mediactrl Architecture October 2007 3. Terminology The following additional terms are defined for use in this document for use in the context of the MediaCtrl Work group in the IETF: Application Server (AS): A functional entity that hosts one or more instances of a communications application. Media Dialog: A SIP dialog between the AS and Media Server that is used for establishing media sessions between a user device such as a SIP phone and the Media Server. Media Functions: Functions available on a Media Server that are used to supply media services to the AS. Some examples are Dual-Tone Multi-Frequency (DTMF) detection, mixing, transcoding, playing announcement, recording, etc. Media Resource Broker (MRB): Assigns specific Media Server resources to incoming calls at the request of service applications (i.e., an AS), which happens in real time as calls come into the network; may acquire knowledge of media server resources utilization that it can use to help decide which MS resources to assign to resource requests from applications; and employs methods/algorithms to determine MS resource assignment. Media Server (MS): A functional entity whose main task is to supply real time media related functions to communication applications. In the architecture for the 3GPP IP Multimedia Subsystem (IMS) a Media Server is referred to as a Media Resource Function (MRF). Media Services: Application service requiring media functions such as Interactive Voice Response (IVR) or Media conferencing. Media Session: From the Session Description Protocol (SDP) specification (RFC 4566 [2]): "A multimedia session is a set of multimedia senders and receivers and the data streams flowing from senders to receivers. A multimedia conference is an example of a multimedia session." MS Control Channel: The connection between the AS and MS used to exchange MS Control PDUs. MS Control Dialog: A SIP dialog that is used for establishing a control channel between the UA and the MS. Melanchuk Expires April 7, 2008 [Page 5] Internet-Draft Mediactrl Architecture October 2007 MS Control Protocol: The protocol in the MS control channel. Melanchuk Expires April 7, 2008 [Page 6] Internet-Draft Mediactrl Architecture October 2007 4. Architecture Overview A Media Server (MS) is a network device that processes media streams. Examples of media processing functionality include: o Control of the Real-Time Protocol (RTP) [3] streams such as video fast update and flow control using Real-Time Control Protocol (RTCP) feedback [4]. o Mixing of incoming media streams. o Media stream source (for multimedia announcements). o Media stream processing (e.g. transcoding, DTMF detection). o Media stream sink (for multimedia recordings) A MS may supply all or part of the above functionalities to an Application Server (AS). An AS is able to send a particular call to a suitable MS, either through discovery of the capabilities that a specific MS provides or through the use of a Media Resource Broker. The type of processing that a Media Server performs on media streams is specified and controlled by an Application Server. Application Servers are logical entities that are capable of running one or more instances of a communications application. The composition of the application logic is out of scope. Examples of Application Servers that may interact with a Media Server are an AS acting as a Conference 'Focus' as defined in RFC 4353 [5] or an IVR application using a Media Server to play announcements and detect DTMF key presses. Application Servers terminate SIP [6] signaling from SIP User Agents and may terminate other signaling outside the scope of MediaCtrl. They use SIP Third Party Call Control [7] (3PCC) to establish, maintain, and tear down media streams from those SIP UAs to a Media Server. Media streams go directly between SIP User Agents and Media Servers. Media Servers support multiple types of media. Common types include audio and video but others such as text and the Binary Floor Control Protocol (BFCP) [8] are also possible. This basic architecture showing session establishment signaling is shown in Figure 1 below. Melanchuk Expires April 7, 2008 [Page 7] Internet-Draft Mediactrl Architecture October 2007 +-------------+ +--------------+ | | | | | Application | SIP | Media | | Server |<------------------->| Server | | | | | +-------------+ +--------------+ ^ ^ \ | RTP/SRTP \ | (audio/ \ | video/etc) \ | \ v \ +--------------+ \ SIP | | +-------------->| SIP | | User Agent | | | +--------------+ Figure 1: Basic Signalling Architecture The architecture must support a many-to-many relationship between Application Servers and Media Servers. In real world deployments, an Application Server may interact with multiple Media Servers and/or a Media Server may be controlled by more than one Application Server. Application Servers can use the SIP URI as described in RFC 4240 [9] to request basic functions from Media Servers. Basic functions are characterized as requiring no mid-call interactions between the AS and MS. Examples of these functions are simple announcement playing or basic conference mixing where the AS does not need to explicitly control the mixing. Most services however have interactions between the AS and MS during a call or conference. The type of interactions can be generalized as follows: o commands from an AS to an MS to request the application or configuration of a function. The request may apply to a single media stream, multiple media streams associated with multiple SIP dialogs, or to properties of a conference mix. o responses from an MS to an AS reporting on the status of particular command. o notifications from an MS to an AS that report results from commands or notify changes to subscribed status. Melanchuk Expires April 7, 2008 [Page 8] Internet-Draft Mediactrl Architecture October 2007 Commands, responses, and notifications are transported using one or more dedicated control channels between the Application Server and the Media Server. Dedicated control channels provide reliable, sequenced, peer to peer transport for media server control interactions using the Transport Control Protocol (TCP). A dedicated control channel is shown in Figure 2 below. +-------------+ +--------------+ | | | | | Application | MS ctrl channel | Media | | Server |<------------------->| Server | | | | | +-------------+ +--------------+ ^ ^ ^ RTP/SRTP | | | (audio/ | | | video/etc) | | | | | v +---|-v-------+ +-|---v-------+ | +-|-----------+ | | | | | | | SIP | | | | User Agent | |-+ | |-+ +-------------+ Figure 2: Media Server Control Architecture Both Application Servers and Media Servers may interact with other servers for specific purposes beyond the scope of this document. For example Application Servers will often communicate with other infrastructure components that are usually based on deployment requirements in association with links to back-office data stores and applications (e.g. 3GPP Diameter interfaces such as 'Sh', 'Dh'). Media Servers will often retrieve announcements from external file servers. Also, many Media Servers support IVR dialog services using VoiceXML [10]. In this case the MS interacts with other servers using HTTP during standard VoiceXML processing. VoiceXML Media Servers may also interact with speech engines, for example using MRCPv2, for speech recognition and generation purposes. Some specific types of interactions between Application and Media servers are also out of scope for MediaCtrl. MS resource reservation is one such interaction. Also, any interactions between Application Melanchuk Expires April 7, 2008 [Page 9] Internet-Draft Mediactrl Architecture October 2007 Servers, or between Media Servers, are also out of scope. Melanchuk Expires April 7, 2008 [Page 10] Internet-Draft Mediactrl Architecture October 2007 5. SIP Usage The Session Initiation Protocol (SIP) [6] was developed by the IETF for the purposes of initiating, managing and terminating multimedia sessions. The popularity of SIP has grown dramatically since its inception and is now the primary Voice over IP (VoIP) protocol. This includes being selected as the basis for architectures such as the IP Multimedia Subsystem (IMS) in 3GPP and included in many of the early live deployments of VoIP related systems. Media services are not a new concept in IP telephony networks and is a fairly well established technology that uses a wide variety of signaling protocols and techniques. The most popular techniques to date have used a combination of SIP and various markup languages to convey media service requests and responses. As discussed in Section 4 and illustrated in Figure 1, the logical architecture proposed by the 'MediaCtrl' Work group involves interactions between an Application Server (AS) and a Media Server (MS). The SIP interactions can be broken into 'media dialogs' - used between an AS and a MS to establish media sessions between an endpoint and a Media Server, and 'MS control dialogs' - which are used to establish and maintain MS control channels. SIP is the primary signaling protocol for session signaling and should be used for all media sessions directed towards a 'MediaCtrl' compliant Media Server. Media Servers may support other signaling protocols but this type of interaction is out of scope within the context of 'MediaCtrl'. Application Servers may terminate non-SIP signaling protocols but must gateway those requests to SIP when interacting with a MediaCtrl compliant MS. SIP will also be used for the creation, management and termination of the dedicated MS control channel(s). A control channel uses TCP to provide reliable sequenced delivery of MS Control Protocol messages. The Application and Media Servers use the SDP attributes defined in [11] to allow SIP negotiation of a TCP connection. Further details and example flows are provided in the SIP Control Framework [12]. The SIP Control Framework also includes basic control message semantics corresponding to the types of interactions identified in Section 4. It uses the concept of "packages" to allow domain specific protocols to be defined using the Extensible Markup Language (XML) [13] format. The MS Control Protocol may then be defined as one or more packages for the SIP Control Framework. Using SIP for both media and control dialogs provides a number of inherent benefits over other potential techniques. These include: Melanchuk Expires April 7, 2008 [Page 11] Internet-Draft Mediactrl Architecture October 2007 1. The use of SIPs location and rendezvous capabilities, as defined in [14]. This provides core mechanisms for routing a SIP request based on techniques such as DNS SRV and NAPTR records. The SIP infrastructure makes heavy use of such techniques. 2. The security and identity properties of SIP. For example, using TLS for reliably and securely connecting to another SIP based entity. The SIP protocol has a number of Identity mechanisms that can be used. RFC 3261 provides an intra-domain digest based mechanism and [15] defines a certificate based inter domain identity mechanism. SIP with S/MIME provides the ability to secure payloads using encrypted and signed certificate techniques. 3. SIP has extremely powerful and dynamic media negotiation properties as defined in RFC 3261 and RFC 3264 [16]. 4. The ability to select an appropriate SIP entity based on capability sets as discussed in RFC 3840 [17]. This provides a powerful function that allows media servers to convey a specific capability set. An AS is then free to select an appropriate MS based on its requirements. 5. Using SIP also provides consistency with IETF protocols and usages. SIP was intended to be used for the creation and management of media sessions and this provides a correct usage of the protocol. As mentioned previously in this section, Media services using SIP are fairly well understood. Until the creation of the 'MediaCtrl' group, the SIP INFO [18] method was used as the transport vehicle between the AS and MS in some protocols. Using SIP INFO in this way is not advised for a number of reasons which include: o INFO is an opaque request with no specific semantics. A SIP endpoint that receives an INFO request does not know what to do with it based on SIP signaling. o SIP INFO was not created to carry generic session control information along the signaling path and it should only really be used for optional application information e.g. carrying mid-call PSTN signaling messages between PSTN gateways. o SIP INFO traverses the signaling path which is an inefficient use for control messages which should go directly between the AS and MS. Melanchuk Expires April 7, 2008 [Page 12] Internet-Draft Mediactrl Architecture October 2007 o RFC 3261 contains rules when using an un-reliable protocol such as UDP. When a packet reaches a size close to the Maximum Transmission Unit (MTU) the protocol should be changed to TCP. This type of operation is not ideal when constantly dealing with large payloads such as XML formatted MS control messages. Melanchuk Expires April 7, 2008 [Page 13] Internet-Draft Mediactrl Architecture October 2007 6. Media Control for IVR Services One of the functions of a Media Server is to assist an Application Server implementing IVR services by performing media processing functions on media streams. Although IVR is somewhat generic terminology, the scope of media functions provided by a MS addresses the needs for user interaction dialogs. These functions include media transcoding, basic announcements, user input detection (via DTMF or speech) and media recording. A particular IVR or user dialog application typically requires the use of several specific media functions, as described above. The range and complexity of IVR dialogs can vary significantly, from a simple single announcement play-back to complex voice mail applications. As previously discussed, an AS uses SIP [6] and SDP [2] to establish and configure media sessions to a media server. An AS uses the MS control channel, established using SIP, to invoke IVR requests and to receive responses and notifications. This topology is shown in Figure 3 below. +-------------+ SIP +-------------+ | Application |<---------------------------->| Media | | Server | (media & MS Control dialogs) | Server | | | | | | | MS Control Protocol (IVR) | | | |<---------------------------->| (IVR media | | (App logic) | (CtrlChannel) | functions) | +-------------+ +-------------+ ^ ^^ \ || R \ || T \ || P \ || / \ || S \ || R \ || T \ || P \ vv \ call signaling +-----------+ ---------------------------->| UE | (e.g. SIP) +-----------+ Figure 3: IVR Topology Melanchuk Expires April 7, 2008 [Page 14] Internet-Draft Mediactrl Architecture October 2007 The variety in complexity of Application Server IVR services requires support for different levels of media functions from the Media Server as described in the following sub-sections. 6.1. Basic IVR Services For simple basic announcement requests the MS control channel, as depicted in Figure 3 above, is not required. Simple announcement requests may be invoked on the Media Server using the SIP URI mechanism defined in RFC 4240 [9]. This interface allows no user input digit detection and collection and no mid-call dialog control. However, many applications only require basic media services and the processing burden on the media server to support more complex interactions with the AS would not be needed in this case. 6.2. IVR Services with Mid-call Controls For more complex IVR dialogs which require mid-call interaction and control between the Application Server and the Media Server, the MS control channel (as shown in Figure 3 above is used to invoke specific media functions on the Media Server. These functions include, but are not limited to, complex announcements with barge-in facility, user input detection and reporting (e.g. DTMF) to an Application Server, DTMF and speech activity controlled recordings, etc. Composite services, such as play-collect and play-record, are also addressed by this model. Mid-call control also allows Application Servers to subscribe to IVR related events and for the Media Server to notify these events when they occur. Examples of such events are announcement completion events, record completion events, and reporting of collected DTMF digits. 6.3. Advanced IVR Services Although IVR Services with Mid-call Control, as described above, provides a comprehensive set of media functions expected from a Media Server, the Advanced IVR Services model allows a higher level of application logic, as provided by VoiceXML, to be executed on the Media Server. Invocation of VoiceXML IVR dialogs may be via the 'Prompt and Collect' mechanism of RFC 4240. Additionally, VoiceXML dialog services may be invoked over the MS control channel, as shown in Figure 3 above. VoiceXML IVR services invoked on the Media Server require an HTTP interface between the Media Server and one or more back-end servers that host or generate VoiceXML documents. These server(s) may or may not be physically separate from the Application Sever. Melanchuk Expires April 7, 2008 [Page 15] Internet-Draft Mediactrl Architecture October 2007 7. Media Control for Conferencing Services RFC 4353 [5] describes the overall architecture and protocol components needed for multipoint conferencing using SIP means. The framework for centralized conferencing [19] [draft-ietf-xcon-framework-08] extends the framework to include a protocol between the user and the conferencing server. RFC 4353 describes the conferencing server decomposition but leaves the specifics open. This section describes the decomposition and discusses the functionality of the decomposed functional units. The conferencing factory and the conference focus are part of the Application Server described in this document. An Application Server uses SIP Third Party Call Control [7] to establish media sessions from SIP user agents to a Media Server. The same mechanism is used by the Application Server as described in this section to add/remove participants to/from a conference, as well as to handle the involved media streams set up on a per-user basis. Since the XCON framework has been conceived as protocol-agnostic when talking about the Call Signaling Protocol used by users to join a conference, an XCON-compliant Application Server will have to take care of gatewaying non-SIP signaling negotiations, in order to set up and make available valid SIP media session between itself and the Media Server, while still keeping the non-SIP interaction with the user in a transparent way. Melanchuk Expires April 7, 2008 [Page 16] Internet-Draft Mediactrl Architecture October 2007 +------------+ +------------+ | | SIP (2m+1c) | | | Application|-------------| Media | | Server | | Server | | (Focus) |-------------| (Mixer) | | | CtrlChannel | | +------------+ +------------+ | \ .. . | \\ RTP... . | \\ .. . | H.323 \\ ... . SIP | \\ ... .RTP | ..\ . | ... \\ . | ... \\ . | .. \\ . | ... \\ . | .. \ . +-----------+ +-----------+ |Participant| |Participant| +-----------+ +-----------+ Figure 4: Conference Topology To complement the functionality provided by 3PCC and by XCON control protocol, the Application Server makes use of a dedicated media server control channel in order to set up and manage media conferences on the media server. Figure Figure 4 shows the signaling and media paths for a two participant conference. The three SIP dialogs between the AS and MS establish two media sessions (2m) from participants, one originally signaled using H.323 and then gatewayed into SIP, and one control session (1c). As a conference focus, the Application Server is responsible for setting up and managing a media conference on the media servers, in order to make sure that the all media streams provided in a conference are available to its participants. This is achieved by recurring to the services of one or more mixer entities, as described in RFC4353, whose role as part of the Media Server is described in this section. Services required by the Application Server include, but are not limited to, means to set up, handle and destroy a new media conference, adding and removing participants from a conference, managing media streams in a conference, control the layout and the mixing configuration for each involved media, allow per-user custom media profiles and so on. As a mixer entity, in such a multimedia conferencing scenario the Melanchuk Expires April 7, 2008 [Page 17] Internet-Draft Mediactrl Architecture October 2007 Media Server receives a set of media streams of the same type (possibly after transcoding) and then takes care of combining the received media in a type-specific manner, redistributing the result to each authorized participant. The way each media is combined, as well as the media-related policies, is properly configured and handled by the Application Server by means of a dedicated MS control channel. To summarize the AS needs to be able to manage media mixers at a conference and participant level. 7.1. Creating a New Conference When a new conference is created, as a result of a previous conference scheduling or of first participant dialing in to a specified URI, the Application Server must take care of appropriately creating a media conference on the Media Server. It does so by placing an explicit request to the Media Server. This can be by means of a MS control channel message. This request may contain detailed information upon the desired settings and policies for the conference (e.g. the media to involve, the mixing configuration for them, relevant identifiers, etc.). The Media Server validates such a request and takes care of allocating the needed resources to set up the media conference. There is another way using SIP methods like [9] or [20] using pre- defined conference profiles and then using the MS control channel afterwards to control the conference if needed. Once done, the MS informs the Application Server about the result of the request. Each conference will be referred to by a specific identifier, which both the Application Server and the Media Server will include in subsequent transactions related to the same conference (e.g. to modify the settings of an extant conference). 7.2. Adding a Participant To a Conference As stated before, an Application Server uses SIP 3PCC to establish media sessions from SIP user agents to a Media Server. The same mechanism is used by the Application Server to add participants to a conference. When a SIP UA places an INVITE to a URI associated with an existing conference, the Application Server forwards it to the MS associated with the conference. The AS as a 3PCC correlates the media session negotiation between the UA and the MS, in order to appropriately establish all the needed media streams based on the conference policies. Melanchuk Expires April 7, 2008 [Page 18] Internet-Draft Mediactrl Architecture October 2007 7.3. Media Controls The XCON Common Data Model [21] currently defines some basic media- related controls, which conference-aware participants can take advantage of in several ways, e.g. by means of a XCON conference control protocol or IVR dialogs. These controls include the possibility to modify the participants own volume for audio in the conference, configure the desired layout for incoming video streams, mute/unmute oneself and pause/unpause one's own video stream. Such controls are exploited by conference-aware participants through the use of dedicated conference control protocol requests to the Application Server. The Application Server takes care of validating such requests and translates them into the Media Server Control Protocol, before forwarding them over the MS Control Channel to the MS. According to the directives provided by the Application Server, the Media Server manipulates the involved media streams accordingly. +------------+ +------------+ | | 'Include audio | | | Application| sent by user X | Media | | Server | in conf Y mix' | Server | | (Focus) |----------------->| (Mixer) | | | (MS CtrlChn) | | +------^-----+ +------------+ | .. | ... | 'Unmute me' ... RTP | (XCON) ... | ... | ... +-----------+ ... |Participant|... +-----------+ Figure 5: Conferencing Example: Unmuting A Participant The media server may need to inform the AS of events like in-band DTMF tones during the conference. 7.4. Floor Control The XCON framework introduces "floor control" functionality as an enhancement upon RFC4575. Floor control is a means to manage joint or exclusive access to shared resources in a (multiparty) conferencing environment. Floor control is not a mandatory mechanism for a conferencing system implementation, but it nonetheless provides Melanchuk Expires April 7, 2008 [Page 19] Internet-Draft Mediactrl Architecture October 2007 advanced media input control features for conference-aware users. Such mechanism allows for a coordinated and moderated access to any set of resources provided by the conferencing system. To do so, a so-called floor is associated to a set of resources, thus representing for users the right to access and manipulate the related resources themselves. In order to take advantage of the floor control functionality, a specific protocol, the Binary Floor Control Protocol, has been specified [22]. RFC4583 [8] provides a way for SIP UAs to set up a BFCP connection towards the Floor Control Server and exploit floor control by means of a COMEDIA negotiation. In the context of the AS-MS interaction, floor control constitutes a further means to control users' media streams. A typical example is a floor associated with the right to access the shared audio channel in a conference. A user who is granted such a floor is granted by the conferencing system the right to talk, which means that its audio frames are included by the MS in the overall audio conference mix. Similarly, when the floor is revoked the user is muted in the conference, and its audio is excluded from the final mix. The BFCP defines a Floor Control Server (FCS) and the Floor chair. It is clear that the floor chair making decisions about floor requests is part of the application logic. This implies that when the floor chair role in a conference is automated, it will normally be part of the AS. The example makes it clear that there can be a direct or indirect interaction between the Floor Control Server and the Media Server, in order to correctly bind each floor to its related set of media resources. Besides, a similar interaction is needed between the Floor Control Server and the Application Server as well, since the latter must be aware of all the associations between floors and resources, in order to opportunely orchestrate the related bindings with the element responsible for such resources (e.g. the Media Server when talking about audio and/or video streams) and the operations upon them (e.g. mute/unmute a user in a conference). For this reason, the Floor Control Server can be co-located with either the Media Server or the Application Server, as long as both elements are allowed to interact with the Floor Control Server by means of some kind of protocol. Though neither of the two topologies is prohibited, the rest of this section will only explore the first scenario, assuming the interaction between AS-FCS to happen through the MS control channel. This scenario is compliant with the H.248.19 document related to conferencing in 3GPP. The second scenario is clear and does not need any specific MS control protocol. The following sequence diagram describes the interaction between the involved parties in a typical scenario. It assumes that a BFCP Melanchuk Expires April 7, 2008 [Page 20] Internet-Draft Mediactrl Architecture October 2007 connection between the UA and the FCS has already been negotiated and established, and that the UA has been made aware of all the relevant identifiers and floors-resources-associations. It also assumes that the AS has previously configured the media mixing on the MS using the MS control channel. This includes identifying the BFCP moderated resources, establishing basic policies and instructions about chair identifiers for each resource, and subscribing to events of interest. A BFCP session has been established between the AS (acting as a floor chair), and the FCS (MS). Every frame the UA might be sending on the related media stream is currently being dropped by the MS, since the UA still isn't authorized to use the resource. For a SIP UA, this state could be consequent to a 'sendonly' field associated to the media stream in a re-INVITE originated by the MS. It is worth pointing out that the AS has to make sure that no user-provided control mechanism, e.g. the CCP mixing controls, can override the floor control, when it is exploited. Melanchuk Expires April 7, 2008 [Page 21] Internet-Draft Mediactrl Architecture October 2007 UA AS MS (Floor Participant) (Floor Chair) (FCS) | | | |<===================== One-way RTP stream ======================| | | | | FloorRequest(BFCP) | | |--------------------------------------------------------------->| | | | | | FloorRequestStatus[PENDING](BFCP) | |<---------------------------------------------------------------| | | FloorRequestStatus[PENDING](BFCP) | | |<-----------------------------------| | | | | | ChairAction[ACCEPTED] (BFCP) | | |----------------------------------->| | | ChairActionAck (BFCP) | | |<-----------------------------------| | | | | | FloorRequestStatus[ACCEPTED](BFCP) | |<---------------------------------------------------------------| | | | . . . . . . | | | | | FloorRequestStatus[GRANTED](BFCP) | |<---------------------------------------------------------------| | | 'Floor has been granted' (CtrlChn) | | |<-----------------------------------| | | | |<==================== Bidirectional RTP stream ================>| | | | . . . . . . Figure 6: Conferencing Example: Floor Control Call Flow A UA, which also acts as a floor participant, sends a 'FloorRequest' to the floor control server (FCS, which is collocated with the MS), stating his will to be granted the floor associated with the audio stream in the conference. The MS answers the UA with a 'FloorRequestStatus' message with a PENDING status, meaning that a decision upon the request has not been taken yet. It then notifies the AS, which in this example handles the floor chair role, about the new request by forwarding there the received request. The AS, according to the BFCP policies for this conference, takes a decision upon the request, i.e. accepting it. It informs the MS about its decision through a BFCP 'ChairAction' message. The MS then Melanchuk Expires April 7, 2008 [Page 22] Internet-Draft Mediactrl Architecture October 2007 acknowledges the 'ChairAction' message and then notifies the UA about the decision with a new 'FloorRequestStatus', this time with an ACCEPTED status in it. The accepted status of course only means that the request has been accepted, which doesn't mean the floor has been granted yet. Once the queue management in the MS, according to the specified algorithms for scheduling, states that the floor request previously made by the UA can be granted, the MS sends a new 'FloorRequestStatus' to the UA with a GRANTED status, and takes care of unmuting the user in the conference. Once the UA receives the notification stating his request has been granted, he can start sending its media, aware of the fact that now his media stream won't be dropped by the MS. In case the session has been previously updated with a 'sendonly' associated to the media stream, the MS must originate a further re-INVITE stating that the media stream flow is now bidirectional ('sendrecv'). This scenario envisages an automated floor chair role, where it's the AS, according to some policies, which takes decisions upon floor requests. The case of a chair role impersonated by a real person is exactly the same, with the difference that the incoming request is not forwarded to the AS but to the floor control participant the UA is exploiting. The decision upon the request is communicated by means of a ChairAction message in the same way. Another typical scenario is a BFCP-moderated conference with no chair managing floor request. In such a scenario, the MS has to take care of incoming request according to some predefined policies, e.g. always accepting new requests. In this case, no decisions are required by external entities, since all is instantly decided by means of policies in the MS. As stated before, the case of the FCS co-located with the AS is much simpler to understand and exploit. When the AS has full control upon the FCS, including its queues management, the AS directly instructs the MS according to the floor status changes, e.g. by instructing the MS through the control channel to unmute a user who has been granted the floor associated to the audio media stream. Melanchuk Expires April 7, 2008 [Page 23] Internet-Draft Mediactrl Architecture October 2007 8. Acknowledgments The authors would like to thank Spencer Dawkins for detailed reviews and comments, Gary Munson for suggestions, and Xiao Wang for review and feedback. Melanchuk Expires April 7, 2008 [Page 24] Internet-Draft Mediactrl Architecture October 2007 9. Security Considerations Security Considerations to be included in later versions of this document. Melanchuk Expires April 7, 2008 [Page 25] Internet-Draft Mediactrl Architecture October 2007 10. Contributors This document is a product of the Media Control Architecture Design Team. In addition to the editor, the following individuals comprised the design team and made substantial textual contributions to this document: Chris Boulton: cboulton@ubiquity.net Martin Dolly: mdolly@att.com Roni Even: roni.even@polycom.co.il Lorenzo Miniero: lorenzo.miniero@unina.it Adnan Saleem: Adnan.Saleem@radisys.com Melanchuk Expires April 7, 2008 [Page 26] Internet-Draft Mediactrl Architecture October 2007 11. References 11.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 11.2. Informative References [2] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [3] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [4] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 2006. [5] Rosenberg, J., "A Framework for Conferencing with the Session Initiation Protocol (SIP)", RFC 4353, February 2006. [6] 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. [7] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo, "Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April 2004. [8] Camarillo, G., "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, November 2006. [9] Burger, E., Van Dyke, J., and A. Spitzer, "Basic Network Media Services with SIP", RFC 4240, December 2005. [10] Lucas, B., Hunt, A., Danielsen, P., Tryphonas, S., Rehor, K., Burnett, D., Carter, J., Ferrans, J., McGlashan, S., and B. Porter, "Voice Extensible Markup Language (VoiceXML) Version 2.0", World Wide Web Consortium Recommendation REC-voicexml20- 20040316, March 2004, . [11] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005. Melanchuk Expires April 7, 2008 [Page 27] Internet-Draft Mediactrl Architecture October 2007 [12] Boulton, C., "A Control Framework for the Session Initiation Protocol (SIP)", draft-ietf-mediactrl-sip-control-framework-00 (work in progress), September 2007. [13] Bray, T., Paoli, J., Sperberg-McQueen, C., Yergeau, F., and E. Maler, "Extensible Markup Language (XML) 1.0 (Fourth Edition)", World Wide Web Consortium Recommendation REC-xml-20060816, August 2006, . [14] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, June 2002. [15] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [16] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [17] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [18] Donovan, S., "The SIP INFO Method", RFC 2976, October 2000. [19] Barnes, M., "A Framework for Centralized Conferencing", draft-ietf-xcon-framework-09 (work in progress), August 2007. [20] Johnston, A. and O. Levin, "Session Initiation Protocol (SIP) Call Control - Conferencing for User Agents", BCP 119, RFC 4579, August 2006. [21] Novo, O., "Conference Information Data Model for Centralized Conferencing (XCON)", draft-ietf-xcon-common-data-model-05 (work in progress), April 2007. [22] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control Protocol (BFCP)", RFC 4582, November 2006. Melanchuk Expires April 7, 2008 [Page 28] Internet-Draft Mediactrl Architecture October 2007 Author's Address Tim Melanchuk (editor) Rain Willow Communications Email: tim.melanchuk@gmail.com Melanchuk Expires April 7, 2008 [Page 29] Internet-Draft Mediactrl Architecture October 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Melanchuk Expires April 7, 2008 [Page 30]