ICE Candidate Removal: Remove ICE candidates when they are no longer useful.

In certain network conditions, ICE agents may find that a local ICE candidate is no longer useful and that the remote ICE agent should not attempt to use that ICE candidate. For example, if an ICE agent is gathering TURN candidates and finds a set of better candidates (such as using UDP to the TURN server) than candidates already signaled (such as using TCP to the TURN server), it may choose to deallocate the worse candidates. But if it does so, the remote ICE agent may waste time and resources attempting to use the deallocated TURN candidates. Just as trickle-ice optimizes ICE by signaling the addition of an ICE candidate, this extension optimizes further by signaling the removal of an ICE candidate.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in . This specification makes use of all terminology defined by the protocol for Interactive Connectivity Establishment in . The messsage signaled between ICE agents that a candidate is removed. An ICE candiate for which a removal signal is sent. The ICE agent that sends the removal signal. The ICE agent that receives the removal signal.

This specification does not define the usage of candidate removal with any specific signaling protocol. However, it will be noted that any signaling protocol must be able to unique identify the Removed Candidates. For example, a combination of the component, ip address, protocol (UDP or TCP), and port would unique identify a Removed Candidate.

When a removal signal, the Receiving Agent MUST NOT pair the Removed Candiates with any future candidates gathered by the Receiving Agent. The Receiving Agent MAY keep the existing candidate pairs that use the Removed Candidates and behave as though the Removed Candidates had not been removed for those candidate pairs. Why would an Receiving Agent choose not to immediately remove existing candidate pairs? Because the Removing Agent MAY choose to keep the Removed Candidate capable of receiving ICE checks and sending responses so that any ICE checks already sent by the Receiving Agent may continue to work briefly so that media can flow as quickly as possible, even if over a candidate pair that will soon be discarded. Both the Removing Agent and the Receiving Agent SHOULD prioritize candidate pairs with a Removed Candidate lower than those without a Removed Candidate.

This specification requests no actions from IANA.

TODO