Lack of bandwidth: Multiple flows compete for a limited amount of bandwidth.
End-to-end delay (fixed and variable): Packets have to traverse many network devices and links that add up to the overall delay.
Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in more delay.
Packet loss: Packets may have to be dropped when a link is congested.
The four big problems facing converged enterprise networks are as follows:
■ Bandwidth capacity: Large graphics files, multimedia uses, and increasing use of voice and video cause bandwidth capacity problems over data networks.
■ End-to-end delay (both fixed and variable): Delay is the time it takes for a packet to reach the receiving endpoint after being transmitted from the sending endpoint. This period of time is called the "end-to-end delay," and consists of two components:
— Fixed network delay: Two types of fixed delays are serialization and propagation delays. Serialization is the process of placing bits on the circuit. The higher the circuit speed, the less time it takes to place the bits on the circuit. Therefore, the higher the speed of the link, the less serialization delay is incurred. Propagation delay is the time it takes for frames to transit the physical media.
— Variable network delay: Processing delay is a type of variable delay, and is the time required by a networking device to look up the route, change the header, and complete other switching tasks. In some cases, the packet also must be manipulated, as, for example, when the encapsulation type or the hop count must be changed. Each of these steps can contribute to the processing delay.
■ Variation of delay (also called jitter): Jitter is the delta, or difference, in the total end-to-end delay values of two voice packets in the voice flow.
■ Packet loss: Loss of packets is usually caused by congestion in the WAN, resulting in speech dropouts or a stutter effect if the playout side tries to accommodate by repeating previous packets.
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