4. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Readers need to be familiar with the terminology defined in [RFC5389] and NAT Behavioral requirements for UDP [RFC4787].
This specification makes use of the following additional terminology:
ICE Session: An ICE session consists of all ICE-related actions starting with the candidate gathering, followed by the interactions between the ICE agents until all the candidates are released or an ICE restart is triggered.
ICE Agent, Agent: An ICE agent is the protocol implementation involved in the ICE candidate exchange. There are two agents involved in a typical candidate exchange.
Initiating Peer, Initiating Agent, Initiator: An initiating agent is an ICE agent that initiates the ICE candidate exchange process.
Responding Peer, Responding Agent, Responder: A responding agent is an ICE agent that receives and responds to the candidate exchange process initiated by the initiating agent.
Candidate, Candidate Information: A transport address that is a potential point of contact for receipt of data. Candidates also have properties -- their type (server reflexive, relayed, or host), priority, foundation, and base.
Host Candidate: A candidate obtained by binding to a specific port from an IP address on the host.
Server-Reflexive Candidate: A candidate whose IP address and port are a binding allocated by a NAT for an ICE agent after it sends a packet through the NAT to a server.
Peer-Reflexive Candidate: A candidate whose IP address and port are a binding allocated by a NAT for an ICE agent after it sends a packet through the NAT to its peer.
Relayed Candidate: A candidate obtained from a relay server, such as a TURN server.
Candidate Pair: A pair containing a local candidate and a remote candidate.
Checklist: An ordered set of candidate pairs that an ICE agent will use to generate checks.
Valid Pair: A candidate pair whose local candidate equals the mapped address of a successful connectivity-check response.
Controlling Agent: The ICE agent that nominates a candidate pair.
Controlled Agent: The ICE agent that waits for the controlling agent to nominate a candidate pair.
Selected Pair, Selected Candidate Pair: The candidate pair used for sending and receiving data for a component of a data stream.