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| 8.1 |  | Quality of Service Requirements |
| 8.1.3 |  | Delay or latency |

Delay or latency refers to the time it takes for a packet to travel from the source to the destination. Delay is comprised of fixed and variable delays. Fixed delays comprise such events as serialization and encoding/decoding. For example, a bit takes a fixed 100ns to exit a 10Mb Ethernet interface. Variable delays are often the result of congestion and include the time packets spend in network buffers waiting for access to the media. In general, delay resulting from bi-directional network traffic is a more significant problem as the delays tend to be additive. Examples of bi-directional traffic include Telnet sessions to a remote host, in which delay manifests itself as the slow acceptance of keystrokes, and voice traffic. The resulting latency makes it difficult to conduct a conversation without talking over the other party.

As a design rule, the total time it takes a voice packet to cross the network should be less than 150ms.