In WebRTC, probing is a mechanism used to check if more bandwidth is available.

Probing is one of the techniques used for bandwidth estimation.

Traditional bandwidth estimation mechanisms rely on packet loss and inter-frame delay. When using these techniques for increasing bandwidth, the level of confidence as to how much the bandwidth estimation can grow is low, leading to slow increase in bandwidth estimation even when more capacity is available.

Probing, on the other hand, is used to try and aggressively increase bandwidth estimation while keeping the estimate accurate. It is done by sending dedicated probing packets that can be disregarded without any degradation to media quality.

WebRTC uses this mechanism at the beginning of a session in order to reach bitrates of 2mbps or more within a second or two of starting the session. It also uses this technique throughout the session as needed.