Computer Networking and Management Lesson 1



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Computer Networks and Internet - Overview
Things to Remember: Packets queue in router buffers Packet arrival rate to link exceeds output link capacity
Packets queue, wait for turn
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Types of Delay
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Processing delay - the time required to examine the packet's header and determine whereto direct the packet is part of the processing delay. The Computer Networking and Management
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processing delay can also include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet's bits from the upstream router to router A. Processing delays in high-speed routers are typically on the order of microseconds Oi less. After this nodal processing, the router directs the packet to the queue that precedes the link to routei Bl bQueuing delay - at the queue, the packet experiences a queuing delay as it waits to be transmitted onto the link. The queuing delay of a specific packet will depend on the number of other, earlier -arriving packets that are queued and waiting for transmission across the link. The delay of a given packet can vary significantly from packet to packet. If the queue is empty and no other packet is currently being transmitted, then our packet's queuing delay is zero. On the other hand, if the traffic is heavy and many other packets are also waiting to be transmitted, the queuing delay will belong. We will see shortly that the number of packets that an arriving packet might expect to find on arrival is a function of the intensity and nature of the traffic arriving to the queue. Queuing delays can be on the order of milliseconds to microseconds in practice. l

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