346 CHAPTER 8 Performance Architecture This is compared with the SLA specificati

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346 CHAPTER 8 Performance Architecture This is compared with the SLA specification (1.5 MBits/second) and found to be non-confoming. Sabsequent packets are then forwarded to a shaper queue, where they are delayed by an average of 10m. As a result, only 100 packets can be transmitted per second, and the rate of that traffic flow becomes (100 packets/second).(1500 byte packets).(8 bits/byte) = 1.2 MBits/second Shaping continues either for a specified period of time or until the traffic low is again conforming. The most serious action that can be taken on traffic is dropping, or discarding packets. This is done when a traffic flow is seriously exceeding its performance boundary, or when the network device is congested to the point where dropping packets is necessary. Traffic conditioning functions are shown in Figure 8.5. Once traffic has been prioritized and conditioned, it is forwarded to one or more output queues for transmission onto the network. Scheduling is the mechanism that determines the order in which traffic is processed for transmission. Scheduling uses prioriy kevels to determine which traffic flows get processed first and most oftern. Scheduling is applied at network devices throughout a network. In most network devices, such as switches and routers, scheduling is provided through network management, or as part of the QoS implementation in that device. Scheduling may be proprietary (enterprise-specific) or standards-based. Some commonly used standard scheduling algorithms include weighted fair queuing (WFQ) and class-based queuing (CBQ). These algorithms provide some degree of fairness in queuing whale allowing relative priority levels (weights) The combination of QoS, prioritization, traffic management, and scheduling provides a comprehensive set of mechanisms that can be applied across a network Packets wit Priority Scheduing FIGURE B.5 Traffic Conditioning Functions

Explanation / Answer

FIFO is the most simple queuing mechanism where it relies on the principle of first in and first out. The main limitation with the fifo model is that it does not set any priority for the incoming packets in the network and treats each and every packet fairly. Also in fifo greedy can take up most of the queue space causing problems.

Class based queuing is the mechainsm which allows network to share bandwidth equally. It is based on the type of class defined by the queuing mechanism. Each packet in the network is based on a class and the classes priority are decided.

WFQ - WFQ is also known as bit by bit round robin because in this mechanism the queuing and scheduling of the incoming data is based on the bits rather than on the packets. All the computation are based on the bits in this algorithm. The main drawback of this is that it is very resource extensive as it compares each and every bit in the network.

Random Early detection - It is the queuing method mostly suited for avodiing network congestion. It basically monitors all the packet size and based on the average queue size and probability of packets it drops the packets if required. The problem is that since only probablity of the packets were considered there was no priority of the packets.

WRED - Weighted red solved the problem with red method where we can have different probabilities for different priorities or queues in the network. It can be used in the network but only if all the queus are given different probabilities.

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