Jitter is a variable-length delay that can cause a conversation to break and become unintelligible. Jitter is not usually a problem with PSTN calls because the bandwidth of calls is fixed. However, in VoIP networks where existing data traffic might be bursty, jitter can occur. On relatively slow links, such as WAN connections, large data packets can take a long time to transmit onto the network. When these large packets are mixed with smaller voice packets, the excessive transmission time can lead to both delay and jitter.
Compression reduces the amount of digital information contained in a particular voice transmission.
The quality of compressed VoIP packets has improved and many different compression algorithms are available. The more a digital VoIP packet is compressed, however, the more likely that voice quality will decrease. When considering compression, it is important to compare the importance of voice quality to potential bandwidth savings. Because compression optimizes bandwidth, significant monthly cost savings are possible. Traditional voice conversations consume 64 Kb of network bandwidth.