Packet Loss occurs over IP networks. It is part of the design of the network itself.

Packet Loss can occurs due to two main reasons:

1. Corruption, when the signal passing through the network  corrupts, getting misdelivered
2. Congestion, when the packets are dropped somewhere along the way due to a congestion in one or more network devices

There are generally 3 ways of dealing with packet losses:

1. Concealment
2. Retransmission
3. Forward Error Correction

All of these techniques are employed by WebRTC in different ways for different types of packet loss.