ONT10第二章IntroducingQoS01.pptVIP

Introduction to IP QoS Introducing QoS Converged Network Quality Issues Converged traffic characteristics: Constant small-packet voice flow competes with bursty data flow. Critical traffic must get priority. Voice and video are time-sensitive. Brief outages are not acceptable. Converged Network Quality Issues (Cont.) Lack of bandwidth: Multiple flows compete for a limited amount of bandwidth. End-to-end delay (fixed and variable): Packets have to traverse many network devices and links that add up to the overall delay. Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in increased delay. Packet loss: Packets may have to be dropped when a link is congested. Lack of Bandwidth Maximum available bandwidth equals the bandwidth of the slowest link. Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application. A lack in bandwidth can have performance impacts on network applications. Bandwidth Availability Upgrade the link (the best but also the most expensive solution). Forward the important packets first. Compress the payload of Layer 2 frames (it takes time). Compress IP packet headers. Efficient Use of Available Bandwidth Using advanced queuing and header compression mechanisms, the available bandwidth can be used in a much more efficient way: Voice: LLQ and RTP header compression Interactive traffic: CBWFQ and TCP header compression Types of Delay Processing delay: The time it takes for a router to take the packet from an input interface, examine it, and put it into the output queue of the output interface. Queuing delay: The time a packet resides in the output queue of a router. Serialization delay: The time it takes to place the “bits on the wire.” Propagation delay: The time it takes for the packet to cross the link from one end to the other. The Impact of Delay on Quality End-to-end delay equals the sum of all propagation, processing, serialization, and queuing de