1.1 Glossary
This document uses the following terms:
200 OK: A response to indicate that the request has succeeded.
Audio/Video Multipoint Control Unit (AVMCU): A Multipoint Control Unit (MCU) that supports audio-video (AV) conferencing.
codec: An algorithm that is used to convert media between digital formats, especially between raw media data and a format that is more suitable for a specific purpose. Encoding converts the raw data to a digital format. Decoding reverses the process.
conference: A Real-Time Transport Protocol (RTP) session that includes more than one participant.
data type: A property of a field that defines the kind of data that is stored in the field, or defines the kind of data returned by an expression when the expression is evaluated.
dialog: A peer-to-peer Session Initiation Protocol (SIP) relationship that exists between two user agents and persists for a period of time. A dialog is established by SIP messages, such as a 2xx response to an INVITE request, and is identified by a call identifier, a local tag, and a remote tag.
endpoint: A device that is connected to a computer network.
endpoint identifier (EPID): A unique identifier of a Session Initiation Protocol (SIP) endpoint. It is formed by combining the value of an epid parameter in a From or To header field with the address-of-record in the corresponding header field.
focus: A single user agent that maintains a dialog and Session Initiation Protocol (SIP) signaling relationship with each participant, implements conference policies, and ensures that each participant receives the media that comprise the tightly coupled conference.
Interactive Connectivity Establishment (ICE): A methodology that was established by the Internet Engineering Task Force (IETF) to facilitate the traversal of network address translation (NAT) by media.
Internet message: A message, such as an email message, that conforms to the syntax that is described in [RFC2822].
INVITE: A Session Initiation Protocol (SIP) method that is used to invite a user or a service to participate in a session.
MCU-Conference-URI: A literal that specifies a URI that can be used to access conferencing services in the context of a Multipoint Control Unit (MCU).
Media Source ID (MSI): A 32-bit identifier that uniquely identifies an audio or video source in a conference.
mixer: An intermediate system that receives a set of media streams of the same type, combines the media in a type-specific manner, and redistributes the result to each participant.
Multipoint Control Unit (MCU): A server endpoint that offers mixing services for multiparty, multiuser conferencing. An MCU typically supports one or more media types, such as audio, video, and data.
notification: A process in which a subscribing Session Initiation Protocol (SIP) client is notified of the state of a subscribed resource by sending a NOTIFY message to the subscriber.
participant: A user who is participating in a conference or peer-to-peer call, or the object that is used to represent that user.
Real-Time Transport Protocol (RTP): A network transport protocol that provides end-to-end transport functions that are suitable for applications that transmit real-time data, such as audio and video, as described in [RFC3550].
request message: A Traversal Using Relay NAT (TURN) message that is sent from a protocol client to a protocol server.
SDP answer: A Session Description Protocol (SDP) message that is sent by an answerer in response to an offer that is received from an offerer.
SDP offer: A Session Description Protocol (SDP) message that is sent by an offerer.
server: A replicating machine that sends replicated files to a partner (client). The term "server" refers to the machine acting in response to requests from partners that want to receive replicated files.
Session Description Protocol (SDP): A protocol that is used for session announcement, session invitation, and other forms of multimedia session initiation. For more information see [MS-SDP] and [RFC3264].
Session Initiation Protocol (SIP): An application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. SIP is defined in [RFC3261].
SIP message: The data that is exchanged between Session Initiation Protocol (SIP) elements as part of the protocol. An SIP message is either a request or a response.
synchronization source (SSRC): The source of a stream of RTP packets, identified by a 32-bit numeric SSRC identifier carried in the RTP header so as not to be dependent upon the network address. All packets from a synchronization source form part of the same timing and sequence number space, so a receiver groups packets by synchronization source for playback. Examples of synchronization sources include the sender of a stream of packets derived from a signal source such as a microphone or a camera, or an RTP mixer. A synchronization source may change its data format (for example, audio encoding) over time. The SSRC identifier is a randomly chosen value meant to be globally unique within a particular RTP session. A participant need not use the same SSRC identifier for all the RTP sessions in a multimedia session; the binding of the SSRC identifiers is provided through RTCP. If a participant generates multiple streams in one RTP session, for example from separate video cameras, each MUST be identified as a different SSRC. See [RFC3550] section 3.
Uniform Resource Identifier (URI): A string that identifies a resource. The URI is an addressing mechanism defined in Internet Engineering Task Force (IETF) Uniform Resource Identifier (URI): Generic Syntax [RFC3986].
user agent client (UAC): A logical entity that creates a new request, and then uses the client transaction state machinery to send it. The role of UAC lasts only for the duration of that transaction. In other words, if a piece of software initiates a request, it acts as a UAC for the duration of that transaction. If it receives a request later, it assumes the role of a user agent server (UAS) for the processing of that transaction.
XML: The Extensible Markup Language, as described in [XML1.0].
XML element: An XML structure that typically consists of a start tag, an end tag, and the information between those tags. Elements can have attributes and can contain other elements.
XML schema: A description of a type of XML document that is typically expressed in terms of constraints on the structure and content of documents of that type, in addition to the basic syntax constraints that are imposed by XML itself. An XML schema provides a view of a document type at a relatively high level of abstraction.
MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.