Introduces a field trial
WebRTC-IncreaseIceCandidatePriorityHostSrflx
that adjusts the priority of non-relay candidates such that the STUN priority attribute calculated as
(prflx-type-preference << 24) | (priority & 0x00FFFFFF)
as described in
https://www.rfc-editor.org/rfc/rfc5245#section-7.1.2.1
will satisfy the condition that the STUN priority of server-reflexive candidates will always be higher than the STUN priority of relay candidates.
Previously this was not the case because the TURN relay preference was added to the local_preference for relay candidates, making it higher than the local_preference of srflx candidates gathered from the same interface.
This led to cases where the resulting candidate pair priority of a srflx-relay pair was higher than the candidate pair priority of a srflx-srflx pair, i.e. using a TURN server in cases that work using a direct P2P connection.
Whether the field trial is active can be observed by checking that
priority-of-srflx-candidate&0x00FFFFFF
is greater than
priority-of-relay-candidate&0x00FFFFFF
BUG=webrtc:13195,webrtc:5813,webrtc:15020
Change-Id: Ib91708fbe7310b6454f93158a45c9d77da009091
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/292700
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40311}
17ec0569c6