QoS Tuning Bandwidth Delay Jitter and Loss

Different types of end-user traffic require different performance characteristics on a network. A file-transfer application might just need throughput, but the delay a single packet experiences might not matter. Interactive applications might need consistent response time. Voice calls need low, consistent delay, and video conferencing needs low, consistent delay as well as high throughput.

Users might legitimately complain about the performance of their applications, and the performance issues may be related to the network. Of course, most end users will believe the network is responsible for performance problems, whether it is or not! Reasonable complaints include the following:

• My application is slow.

• My file takes too long to transfer now.

• The video freezes.

• The phone call has so much delay we keep talking at the same time, not knowing whether the other person has paused.

In some cases, the root problem can be removed, or at least its impact lessened, by implementing QoS features.

So, how do voice, video, and data traffic behave in networks that do not use QoS? Well, certainly the performance varies. Table 1-2 outlines some of the behaviors in a network without QoS.

Table 1-2 Traffic Behavior with No QoS

Type of Traffic	Behavior Without QoS
Voice	Voice is hard to understand.
	Voice breaks up, sounds choppy.
	Delays make interacting difficult; callers do not know when other party has finished talking.
	Calls are disconnected.
Video	Picture displays erratically; jerky movements.
	Audio not in sync with video.
	Movement slows down.
Data	Data arrives after it is no longer useful.
	Customer waiting for customer care agent, who waits for a screen to display.
	Erratic response times frustrate users, who may give up or try later.

QoS attempts to solve network traffic performance issues, although QoS is not a cure-all. To improve network performance, QoS features affect a network by manipulating the following network characteristics:

Continue reading here: Bandwidth

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