Traffic Characteristics of Voice Video and Data
So why do you need QoS? QoS can affect a network's bandwidth, delay, jitter, and packet loss properties. Applications have different requirements for bandwidth, delay, jitter, and packet loss. With QoS, a network can better provide the right amounts of QoS resources for each application. Table 1-10 lists some major application categories, along with their typical needs for network resources and behavior.
Table 1-10 Applications and Their QoS Needs
|
Bandwidth |
Delay |
Jitter |
Loss |
|
|
Interactive |
Low |
Low |
Medium/high |
Low |
|
Batch |
High |
High |
High |
Low |
|
Voice |
Low |
Low |
Low |
Low |
|
Interactive Video |
High |
Low |
Low |
Low |
|
1-Way Video |
High |
Medium/high |
Low |
Low |
|
"Fragile" (For Instance, SNA*) |
Low |
Low |
Medium/high |
None |
* SNA = Systems Network Architecture
* SNA = Systems Network Architecture
The table states the QoS requirements of different applications. For instance, interactive data applications typically don't need much bandwidth, although one might argue that a lot of web applications do require a lot of bandwidth. Similarly, voice requires relatively little bandwidth, but requires low delay and low jitter; otherwise, the voice quality suffers significantly. Interactive video, such as video conferencing, has the same characteristics as voice, except it requires much more bandwidth. One-way video, however, can tolerate with long delays, so long as jitter does not exceed the jitter buffer on the receiving side. If you are watching a video over the Internet, for example, and if it takes 20 seconds to start, but it looks and sounds good for the next half hour, you really don't care that the average packet is taking 10 seconds to traverse the network.
The QoS course specifically mentions a category calledfragile, implying that some applications are totally intolerant of packet loss. I personally would not put SNA in this category—I included it in the book, however, because it is in a table from the QoS course, which of course is the basis for the CCIP QoS Exam questions
The next three sections cover voice, video, and data flows.
Continue reading here: Voice Basics
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