e, packets for a specified period of time before forwarding but also on configurations such as access lists, queuing them to the decompression process. A jitter buffer is methods, and transmission modes. Delay (latency) can designed to smooth packet flow. In doing so, it can also have a noticeable effect but can be controlled somewhat in add packet delay. Jitter buffers should be dynamic to give a private environment (LAN/WAN) because the com- the best quality, or if static, should generally be sized to pany or enterprise manages the network infrastructure or twice the largest statistical variance between packets. SLA (Service Level Agreement). When using the public Router vendors have many queuing methods that alter network, there are inherent delays that one cannot the behavior of the jitter buffer. It is not enough to just control. select the right size of jitter buffer, one must also pair an VoIP network vendors give many differing guidelines appropriate queue-unloading algorithm type with the as to the amount of delay that is acceptable to maintain jitter buffer. The network topology can also affect jitter. good voice quality. A good set of guidelines for voice Because there are fewer collisions on a data-switched quality is network than on a hub-based network, there will be less jitter on the switched network. Under 150-200 ms delay can give very good voice quality. Delays exceeding 200 ms may still be quite accept- Packet loss able depending on customer expectations, analog trunks used, codec type, etc. Network packet loss occurs when packets are sent, but The H.323 protocol defines a maximum end-to-end not received at the final destination due to some network delay of 400ms. Delays beyond this level can cause problem. Qualifying problems caused by occasional network instability. packet loss are difficult to detect because each codec has (These numbers are for delay between endpoints, its own packet loss concealment method. Therefore, it is meaning LAN/WAN measurements not including IP possible that voice 