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Session 2

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Delay, Loss, and Throughput in Packet-Switched Networks

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• Processing Delay: The time required to examine the packet’s header and determine where to direct thepacket is part of the processing delay.

Delay, Loss, and Throughput in Packet-Switched Networks

• Queuing Delay: At the queue, the packet experiences a queuing delay as it waits to be transmitted onto the link

• Transmission Delay: Assuming that packets are transmitted in a first-come-first-served manner, as is common in packet-switched networks, our packet can be transmitted only after all the packets that have arrived before it have been transmitted.

The transmission delay is L/R R: transmission rate (bits/sec)L: length of the packet by L bits

• Propagation Delay: The time required to propagate from the beginning of the link to router B is the propagation delay.

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• Comparing Transmission and Propagation DelayThe transmission delay is the amount of time required for the router to push out the packet; it is a functionof the packet’s length and the transmission rate of the link, but has nothing to do with the distance between the two routers. The propagation delay, on the other hand, is the time it takes a bit to propagate from one router to the next; it is a function of the distance between the two routers, but has nothing to do with the packet’s length or thetransmission rate of the link.

Delay, Loss, and Throughput in Packet-Switched Networks

• Nodal delay

• Queuing Delay and Packet Loss

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• Traffic intensity

La/RL: packet lengtha: average rate at which packets arrive at the queue( packet/sec)R: Transmission rate (bits/sec)

Design your system so that the traffic intensity is no greater than 1.

Delay, Loss, and Throughput in Packet-Switched Networks

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• End-to-End Delay

N - 1 routers And Uncongested ( no queueing )

Delay, Loss, and Throughput in Packet-Switched Networks

• Traceroute (RFC 1393)

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• Throughput in Computer Networks

Delay, Loss, and Throughput in Packet-Switched Networks

throughput =min{Rs, Rc}.

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Protocol Layers and Their Service Models

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Networks Under Attack

• Malware• Viruses• Worm

• Attack servers and network infrastructure• Denial-of-service (DoS) attacks • Vulnerability attack• Bandwidth flooding: The attacker sends a deluge of packets to the

targeted host.• Connection flooding. The attacker establishes a large number of half-

open or fully open TCP connections at the target host.

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Networks Under Attack

• Sniff packets• Masquerade as someone you trust

• IP spoofing (The ability to inject packets into the Internet with a false source address)