Jitter buffers also must be tuned to their maximum, as again, routed networks do not guarantee that all packets will take the same route to their destination. Jitter buffers must dynamically adjust to the changing conditions in the network. Echo, as another example, depends heavily on delay. Echo becomes imperceptible when it returns so fast that there is no distinguishable difference between it and the reference signal. Again, echo cancellers must be tuned to the proper amount of delay in the network yet still allow full duplex communication.
Packet loss is a critical issue in voice and voiceband applications.
The ear is a filter and transducer, so it is more tolerant to instant quality degradation than, say, a fax machine. A single packet loss during a telephone conversation will have no perceptible effect on voice quality, but if we experience a single packet loss during the fax modem training phase of a voiceband application, such as a fax, after the selection of the data rate and modulation scheme have occurred, the modems could either slow down and then retry, or perhaps worse. It is important to understand the optimization parameters of the network and the types of traffic it will be designed to support to set the operating performance points properly. The public network has had years to change and tweak these factors for success, while VoIP pioneers are in a land rush to determine the proper formula and thereby help their companies grab the rewards gained by coming to market first. Unfortunately, time is not on their side, and the proper tools are a must to expediently come to the solution.