1.1 Glossary
This document uses the following terms:
200 OK: A response to indicate that the request has succeeded.
answer: A message that is sent in response to an offer that is received from an offerer.
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].
call: A communication between peers that is configured for a multimedia conversation.
dial plan: The rules that govern the translation of dial strings into SIP and tel URIs, either global or local, as described in [RFC3966].
dial string: The numbers, symbols, and pauses that users enter to place a phone call. It is consumed by one or more network entities and understood in the context of the configuration of those entities. It is used to generate an address-of-record or identifier to route a call.
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.
domain: A set of users and computers sharing a common namespace and management infrastructure. At least one computer member of the set must act as a domain controller (DC) and host a member list that identifies all members of the domain, as well as optionally hosting the Active Directory service. The domain controller provides authentication of members, creating a unit of trust for its members. Each domain has an identifier that is shared among its members. For more information, see [MS-AUTHSOD] section 1.1.1.5 and [MS-ADTS].
E.164: An international public telecommunication numbering plan that is used in the public switched telephone network (PSTN) and some data networks. It defines the format of telephone numbers. E.164 numbers can have a maximum of 15 digits and typically are written with a plus sign (+) prefix.
early media: Media, such as audio and video, that is exchanged before a specific session is accepted by the called user. During a dialog, early media occurs when the initial INVITE is sent, until the user agent server (UAS) generates a final response.
fully qualified domain name (FQDN): An unambiguous domain name that gives an absolute location in the Domain Name System's (DNS) hierarchy tree, as defined in [RFC1035] section 3.1 and [RFC2181] section 11.
gateway: A network edge device that bridges Microsoft Office Communications Server protocols with legacy telephony networks protocols.
INVITE: A Session Initiation Protocol (SIP) method that is used to invite a user or a service to participate in a session.
IP-PBX: A PBX that supports Voice over IP (VoIP).
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].
offer: A message that is sent by an offerer.
P-Asserted-Identity (PAI): A Session Initiation Protocol (SIP) header field, as described in [RFC3325], that is used by trusted entities to carry the identity of the user who is sending an SIP message as it was verified by authentication.
private branch exchange (PBX): A server-based telephony solution that services a specific organization or office.
proxy: A computer, or the software that runs on it, that acts as a barrier between a network and the Internet by presenting only a single network address to external sites. By acting as a go-between that represents all internal computers, the proxy helps protects network identities while also providing access to the Internet.
public switched telephone network (PSTN): Public switched telephone network is the voice-oriented public switched telephone network. It is circuit-switched, as opposed to the packet-switched networks.
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.
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.
SIP transaction: A SIP transaction occurs between a UAC and a UAS. The SIP transaction comprises all messages from the first request sent from the UAC to the UAS up to a final response (non-1xx) sent from the UAS to the UAC. If the request is INVITE, and the final response is a non-2xx, the SIP transaction also includes an ACK to the response. The ACK for a 2xx response to an INVITE request is a separate SIP transaction.
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.
user agent server (UAS): A logical entity that generates a response to a Session Initiation Protocol (SIP) request. The response either accepts, rejects, or redirects the request. The role of the UAS lasts only for the duration of that transaction. If a process responds to a request, it acts as a UAS for that transaction. If it initiates a request later, it assumes the role of a user agent client (UAC) for that transaction.
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.