1.1 Glossary
This document uses the following terms:
200 OK: A response to indicate that the request has succeeded.
audio video profile (AVP): A Real-Time Transport Protocol (RTP) profile that is used specifically with audio and video, as described in [RFC3551]. It provides interpretations of generic fields that are suitable for audio and video media sessions.
Augmented Backus-Naur Form (ABNF): A modified version of Backus-Naur Form (BNF), commonly used by Internet specifications. ABNF notation balances compactness and simplicity with reasonable representational power. ABNF differs from standard BNF in its definitions and uses of naming rules, repetition, alternatives, order-independence, and value ranges. For more information, see [RFC5234].
base64 encoding: A binary-to-text encoding scheme whereby an arbitrary sequence of bytes is converted to a sequence of printable ASCII characters, as described in [RFC4648].
Client Scale Secure Real-Time Transport Protocol (Client Scale-SRTP): A protocol that is used by applications that receive media from and send media to only one peer. It is a variation of the Scale Secure Real-Time Transport Protocol (SSRTP), as described in [MS-SSRTP].
Common Intermediate Format (CIF): A picture format, described in the H.263 standard, that is used to specify the horizontal and vertical resolutions of pixels in YCbCr sequences in video signals.
conference: A Real-Time Transport Protocol (RTP) session that includes more than one participant.
Content-Type header: A message header field whose value describes the type of data that is in the body of the message.
contributing source (CSRC): A source of a stream of RTP packets that has contributed to the combined stream produced by an RTP mixer. The mixer inserts a list of the synchronization source (SSRC) identifiers of the sources that contributed to the generation of a particular packet into the RTP header of that packet. This list is called the CSRC list. An example application is audio conferencing where a mixer indicates all the talkers whose speech was combined to produce the outgoing packet, allowing the receiver to indicate the current talker, even though all the audio packets contain the same SSRC identifier (that of the mixer). See [RFC3550] section 3.
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.
dual-tone multi-frequency (DTMF): In telephony systems, a signaling system in which each digit is associated with two specific frequencies. This system typically is associated with touch-tone keypads for telephones.
endpoint: A device that is connected to a computer network.
forward error correction (FEC): A process in which a sender uses redundancy to enable a receiver to recover from packet loss.
Host Candidate: A candidate that is obtained by binding to ports on the local interfaces of the host computer. The local interfaces include both physical interfaces and logical interfaces such as Virtual Private Networks (VPNs).
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 Protocol version 4 (IPv4): An Internet protocol that has 32-bit source and destination addresses. IPv4 is the predecessor of IPv6.
Internet Protocol version 6 (IPv6): A revised version of the Internet Protocol (IP) designed to address growth on the Internet. Improvements include a 128-bit IP address size, expanded routing capabilities, and support for authentication and privacy.
INVITE: A Session Initiation Protocol (SIP) method that is used to invite a user or a service to participate in a session.
Media Source ID (MSI): A 32-bit identifier that uniquely identifies an audio or video source in a conference.
ms-diagnostics-public header: A header that is added to a Session Initiation Protocol (SIP) response, BYE request, or CANCEL request to convey troubleshooting information. Unlike the ms-diagnostics header, the ms-diagnostics-public header does not contain a "source" parameter.
multiple points of presence (MPOP): A condition in which a single user signs in from multiple devices. A user who has multiple points of presence can be contacted through any of these devices.
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.
Multipurpose Internet Mail Extensions (MIME): A set of extensions that redefines and expands support for various types of content in email messages, as described in [RFC2045], [RFC2046], and [RFC2047].
network address translation (NAT): The process of converting between IP addresses used within an intranet, or other private network, and Internet IP addresses.
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 Control Protocol (RTCP): A network transport protocol that enables monitoring of Real-Time Transport Protocol (RTP) data delivery and provides minimal control and identification functionality, as described in [RFC3550].
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].
Relayed Candidate: A candidate that is allocated on the Traversal Using Relay NAT (TURN) server by sending an Allocate Request to the TURN server.
Remote Desktop Protocol (RDP): A multi-channel protocol that allows a user to connect to a computer running Microsoft Terminal Services (TS). RDP enables the exchange of client and server settings and also enables negotiation of common settings to use for the duration of the connection, so that input, graphics, and other data can be exchanged and processed between client and server.
Scale Secure Real-Time Transport Protocol (SSRTP): A Microsoft proprietary extension to the Secure Real-Time Transport Protocol (SRTP), as described in [RFC3711].
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.
secure audio video profile (SAVP): A protocol that extends the audio-video profile specification to include the Secure Real-Time Transport Protocol, as described in [RFC3711].
Secure Real-Time Transport Protocol (SRTP): A profile of Real-Time Transport Protocol (RTP) that provides encryption, message authentication, and replay protection to the RTP data, as described in [RFC3711].
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.
Server Reflexive Candidate: A candidate whose transport addresses is a network address translation (NAT) binding that is allocated on a NAT when an endpoint sends a packet through the NAT to the server. A Server Reflexive Candidate can be discovered by sending an allocate request to the TURN server or by sending a binding request to a Simple Traversal of UDP through NAT (STUN) server.
Server Scale Secure Real-Time Transport Protocol (Server SSRTP): A derivative of the Scale Secure Real-Time Transport Protocol (SSRTP) that is used by applications to receive media from multiple senders and fan-out media to multiple receivers. Typically, applications such as Multipoint Control Units (MCUs) use this mode of encryption.
session: A collection of multimedia senders and receivers and the data streams that flow between them. A multimedia conference is an example of a multimedia session.
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 protocol client: A network client that sends Session Initiation Protocol (SIP) requests and receives SIP responses. An SIP client does not necessarily interact directly with a human user. User agent clients (UACs) and proxies are SIP clients.
SIP request: A Session Initiation Protocol (SIP) message that is sent from a user agent client (UAC) to a user agent server (UAS) to call a specific operation.
SIP response: A Session Initiation Protocol (SIP) message that is sent from a user agent server (UAS) to a user agent client (UAC) to indicate the status of a request from the UAC to the UAS.
stream: A flow of data from one host to another host, or the data that flows between two hosts.
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 could 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 has to be identified as a different SSRC. See [RFC3550] section 3.
telecommunications device for the deaf (TDD): A device that enables the transmission of typed messages over phone lines. These devices typically include keyboards for typing messages to send and printers to receive messages from one device to another.
Transmission Control Protocol (TCP): A protocol used with the Internet Protocol (IP) to send data in the form of message units between computers over the Internet. TCP handles keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet.
Transport Layer Security (TLS): A security protocol that supports confidentiality and integrity of messages in client and server applications communicating over open networks. TLS supports server and, optionally, client authentication by using X.509 certificates (as specified in [X509]). TLS is standardized in the IETF TLS working group.
update: An add, modify, or delete of one or more objects or attribute values. See originating update, replicated update.
user agent: An HTTP user agent, as specified in [RFC2616].
User Datagram Protocol (UDP): The connectionless protocol within TCP/IP that corresponds to the transport layer in the ISO/OSI reference model.
Video-based Screen Sharing: A protocol that uses video modality to share the client's screen with another client directly or via a multipoint control unit (MCU).
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.