5. Definitions

STUN Agent: An entity that implements the STUN protocol. The entity can be either a STUN client or a STUN server.

STUN Client: An entity that sends STUN requests and receives STUN responses. A STUN client can also send indications. In this specification, the terms STUN client and client are synonymous.

STUN Server: An entity that receives STUN requests and sends STUN responses. A STUN server can also send indications. In this specification, the terms STUN server and server are synonymous.

Transport Address: The combination of an IP address and port number (for example, a UDP or TCP port number).

Reflexive Transport Address: A transport address learned by a client that identifies that client as seen by another host on the IP network (typically a STUN server). When there is an intervening NAT between the client and the other host, the reflexive transport address represents the mapped address allocated to the client on the public side of the NAT. Reflexive transport addresses are learned from the mapped address attribute (MAPPED-ADDRESS or XOR-MAPPED-ADDRESS) in STUN responses.

Mapped Address: Same meaning as reflexive address. This term is retained for historical reasons and due to the naming of the MAPPED-ADDRESS and XOR-MAPPED-ADDRESS attributes.

Long-Term Credential: A username and associated password that represent a shared secret between client and server. Long-term credentials are generally granted to the client when a subscriber provisions a service and persist until the subscriber leaves the service or explicitly changes the credential.

Long-Term Password: The password from a long-term credential.

Short-Term Credential: A temporary username and associated password that represent a shared secret between client and server. Short-term credentials are obtained through some out-of-band protocol mechanism between the client and server, prior to the STUN exchange. A short-term credential has an explicit temporal scope, which may be based on a specific amount of time (such as 5 minutes) or on an event (such as termination of a SIP dialog). The specific scope is defined by the application usage.

Short-Term Password: The password component of a short-term credential.

STUN Indication: A STUN message that does not receive a response.

Attribute: The STUN term for a Type-Length-Value (TLV) object that can be added to a STUN message. Attributes are divided into two types: comprehension-required and comprehension-optional. STUN agents can safely ignore comprehension-optional attributes they don't understand, but cannot successfully process a message if it contains a comprehension-required attribute that is not understood.

RTO (Retransmission TimeOut): Retransmission TimeOut, which defines the initial period between transmission of a request and the first retransmit of that request.