sion Multiplexing) networks and the LAN, or the impedance mismatch between a headset and its 1 percent or less can yield toll quality depending on adapter. Impedance mismatch causes inefficient energy many factors. transfer. The energy imbalance must go somewhere and 3 percent or less should give business communica- SO it is reflected back in the form of an echo. Usually the tions quality. speaker hears an echo but the receiver does not. More than 3 percent may be acceptable for voice but Echo cancellers, which have varying amounts of may interfere with signaling. memory, compare the received voice with the current voice patterns. If the patterns match, the canceller Packet mis-order cancels the echo. Echo cancellers aren't perfect, how- ever. Under some circumstances, the echo gets past the Network packet mis-order is, for VoIP, very much like canceller. The problem is exacerbated in VoIP systems. If packet loss. If a packet arrives out of order, it is generally the one-way trip delay between endpoints is larger than discarded as it makes no sense to play it out of order and the echo canceller memory, the echo canceller won't ever buffers are small. Specifically, packets are discarded find a pattern to cancel. when they arrive later than the jitter buffer can hold them. Mis-order can occur when networks send in- Silence suppression dividual packets over different routes. Planned events such as load balancing, unplanned events such as re- Silence suppression software, often called Voice Activity routing due to congestion, or other transient difficulties Detection (VAD), monitors the received signal for voice can cause packet mis-order. Packets traversing the activity. When no activity is detected for the configured network over different routes may arrive at their desti- period of time, the software informs the Packet Voice nation out of order. Network latency over multiple yet Protocol. This prevents the encoder output from being unequal routing paths can also force packet mis-order. transported across the netwo