Class of Service (CoS) functionality can help optimize network performance. For a successful deployment, network designers should identify all applications, understand requirements associated with each application, designate appropriate mapping for groups of applications and provide mechanisms in the underlying network to deliver CoS. CoS mapping and deployment are important; adhering to tested strategies and avoiding common misconceptions helps IT managers advance optimization across the wide area network.
Point of View
Class of Service:
Myths and Misconceptions
Multinational enterprises are experiencing relentless pressures from CoS Does Not Change the Laws of Physicsinside and outside their organizations fueled by "the perfect storm" There are four sources of packet delay in a typical enterprise1 2of multiple forces colliding - application development, technology environment - forwarding delay , queuing delay, propagation delay3advancements, more savvy and demanding customers and the and serialization delay . Assuming that the enterprise has deployedeconomics of an increasingly competitive marketplace. Utilizing Class the industry standard for hardware-based routers and the accessof Service (CoS) functionality is one method of optimizing network bandwidth is fixed, you have no real control over forwarding delay,performance so that it aligns with the enterprise agenda. propagation delay or serialization delay. The only aspect of packetdelay across the network that can be actually controlled is queuingThere has been much discussion about the valuable benefits of delay. Queuing delay (1/1-U) is best observed by understanding theCoS; however, there are also some common myths, which unless load across the network in both directions. This utilization willchallenged, can impact the success of the CoS implementation. increase the overall time a packet has to wait in transit for the line toThe focus of this paper is to expose the common misconceptions clear. Load on the network can quickly start to increase packet delay;of what CoS can and cannot do. We will also discuss an approach > 70% (for
Without CoS, queuing delay can easily represent the largest delay Working closely with the service provider, IT managers can still developcomponent across the network. When CoS is properly deployed, the a very granular approach to traffic classification and prioritization. Aqueuing delay is minimized and the end-to-end delay is primarily a service provider need not offer the same number of classes that arefunction of the fixed delay components. The deployment of CoS in the defined in the enterprise. QoS transparency allows enterprises to4network does not impact the speed of light in optical fiber, the retain their DSCP code markings such that traffic going through theswitching time of networking equipment or the time taken to transmit service provider network will translate back to the finer-grained classa large packet onto a low speed link. Therefore, even with a proper scheme of the local enterprise network.CoS strategy, any of these remaining delay components can still leadto marginal performance of response-time critical applications. The More Classes of Service You Have - The Better, Right?One of the main tools available for implementing CoS is the intelligentCoS Controls All Aspects of the End-User Experience scheduling of packets. Queuing algorithms are therefore crucialThe end-user's experience is controlled by factors other than CoS. components in effective congestion control as t... [download for more]
