IP-based networks often experience packet loss, and this is a normal part of the network operations. In fact the TCP protocol uses packet loss as its flow control mechanism. TCP determines how quickly to send data by increasing its send rate until packet loss occurs, and then backing off. This occurs over and over for each TCP stream in the network.
The Internet Protocol (IP) is at the heart of all modern networks, and is responsible for connecting one endpoint to another. But by design, IP is an unreliable protocol. This means it is not designed to insure that all packets sent from one endpoint arrive successfully at the other endpoint.
Packet loss is typically due to congested links and routers. Network jitter can result in packet loss.
1% packet loss may produce blocky video and/or audio loss
2% packet loss may make video unusable, although audio may sound somewhat acceptable
above 2% becomes intolerable
While packet loss above 2% is unacceptable for H.323, 1-2% is considered “poor” and should be resolved immediately in consultation with the connectivity / service provider.