Content

| 7.5 |  | Voice Quality Issues |
| 7.5.3 |  | QoS |

QoS
In a converged environment, all types of traffic travel over a single transport infrastructure. Yet all traffic types are not the same. Data is bursty, loss intolerant, and not latency sensitive. Voice, on the other hand, is nonbursty and has some tolerance to loss but is latency sensitive. The challenge is in providing the required level of service for each of these traffic types.

Running both voice and data on a common network requires the proper quality of service (QoS) tools to ensure that the delay and loss parameters of voice traffic are satisfied. These tools are available as features in IP phones, switches, and routers.

Application Considerations for QoS
The specific QoS requirements for given applications are generally determined by three parameters: latency, jitter, and loss. Depending on the type of application to be implemented over a Cisco AVVID Network Infrastructure, the importance and effects of these considerations can differ.

One-way latency for voice or video conferencing should be no more than 150 to 200 ms, streaming video can tolerate up to 4 to 5 second latency. Similarly, jitter is not an issue for streaming video, while it should be limited to 30 ms for voice and video conferencing applications.

Bandwidth effects will also differ. For example, to support video conferencing, the minimum bandwidth guarantee is the size of the video-conferencing session plus 20 percent (a 384 Kbps video-conferencing session requires 460 Kbps guaranteed priority bandwidth). Voice requires 17-to-106 Kbps of guaranteed priority bandwidth per call (depending on the sampling rate, codec and Layer 2 overhead), while 150 bps (plus Layer 2 overhead) per phone of guaranteed bandwidth is required for Voice Control traffic.

Although planning requirements certainly vary depending on application, Cisco AVVID Network Infrastructure capabilities have the flexibility to concurrently support QoS requirements of voice, streaming video, video content distribution, video conferencing, and mission critical data traffic all carried over a common IP-based networking environment.

Traffic Classification Types
The goal of protecting voice traffic from being run over by data traffic is accomplished by classifying voice traffic as high priority and then allowing it to travel in the network before low priority traffic. Classification can be done at Layer 2 or at Layer 3.

Classification is the first step toward achieving quality of service. Ideally, this step should be done as close to the source as possible, usually at the access layer of the network.