Section 10.1: Understanding the Need for Quality of Service

Quality of Service (QoS) addresses the following situations:

• Delay: When packets are transmitted over the network from one host to another, a delay can occur. Packets can arrive later than the time that they expected to arrive. The entire delay from the point that a user enters a key, to the time that the character is echoed and shown in a terminal session, is known as


• Jitter takes place when packets arrive outside established parameters for a delay: earlier or later. Queue disposition can have an impact on delay. Packets at the front of the queue could be prone to delay. The packets to the back are behind an anonymous number of packets. This creates variability. Cisco offers various queuing options that enable the most applicable packets to be opted for on an individual basis.

• Loss: Packets that moves across an error prone network could be dropped. When this happens in a connection oriented network, the lost packet can simply be requested and submitted again. In a connectionless network the packet remains lost.