Problem 5 Imagine that client A needs to send 4 messages reliably to a server B over an unreliable network layer. Assume that A and B use the alternating bit protocol (rdt 3.0). Describe graphi- cally (i.e. draw a labeled diagram of) the sequence of message exchanges resulting when the 2nd message send is lost, and the ack for the 3rd message send is corrupted.

Problem 5 Imagine that client A needs to send 4 messages reliably to a server B over an unreliable network layer. Assume that A and B use the alternating bit protocol (rdt 3.0). Describe graphi- cally (i.e. draw a labeled diagram of) the sequence of message exchanges resulting when the 2nd message send is lost, and the ack for the 3rd message send is corrupted.

Principles of Information Security (MindTap Course List)

6th Edition

ISBN:9781337102063

Author:Michael E. Whitman, Herbert J. Mattord

Publisher:Michael E. Whitman, Herbert J. Mattord

Chapter6: Security Technology: Access Controls, Firewalls, And Vpns

Section: Chapter Questions

Problem 2RQ

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Question 5: Suppose you attach a network monitor to observe the sequence of frames that travel over a link from sender A to receiver B. The problem is to deduce what protocols, if any, could have generated the observed sequence. The following diagrams depict a flow of frames, with their corresponding sequence numbers, from the sender (A). There may be traffic from B to A, which is not depicted in the diagram. A gap between adjacent frames implies passage of time with no transmission from the sender. Note that the x-axis is time, and not space. Justify your answer. A A A ● ● ● ● 1 5 ● 3 5 0 ● 0 0 1 1 1 ● Go-Back-N ● Selective Repeat 1 0 5 0 c) For Diagram 3, the protocol is not: Stop-and-Wait Time Diagram 1 2 Time a) For Diagram 1, the most likely protocol being used is: Stop-and-Wait ● Go-Back-N (if Go-Back-N, give the window size) Selective Repeat (if Selective Repeat, give the window size) Diagram 2 Time 3 Diagram 3 1 Time b) For Diagram 2, the most likely protocol being used is:…
Problem 2. Consider a packet of L bits that is sent over a path of Q links (i.e., a source and destination connected by a sequence of (Q-1) routers or switches). Each link transmits at R bps. This packet is the only traffic transmitted by the network (so there are no queuing delays) and the propagation delay and processing delay at routers are negligible. How long does it take to send this packet from source to destination if the network is: a) a packet-switched datagram network b) a circuit-switched network. Assume that bandwidth of R bps on each link is sliced into five individual circuits, so that cach circuit receives (R/5) bandwidth. Also assume that the circuit setup time is t,.. Give an expression for the number of links Q such that the packet delivery from the sender to the receiver will be faster over the packet-switched network, and the expression for the number of links Q such that the circuit-switched network will be faster.
2. Packet transmission. a. Consider a packet of length L that begins at end system A and travels over 2 links to a destination end system B. These two links are connected by one packet switch. Let d₁, S₁, and R₁ denote the length, propagation speed and transmission rate of link I, for i in {1, 2}. The packet switch delays each packet by dproc b. There is a queuing delay of 100 msec at the switch (but no queuing delay at A). The packet is 1500 bits in length, the propagation speed on all links is 2.5 x 108 m/sec, the transmission rate on both links is 1 Mbps, and the packet switch processing delay is 3 msec. The length of the first link is 4000 km and the second link is 1000 km. What is the end-to-end delay from A to B? c. The switch fails and is replaced. This changes the following information for the switch only. The packet switch processing delay is reduced from 3 msec to 2 msec, the queuing delay is reduced from 100 msec to 40 msec but the second transmission link increases to 8,500…
Consider a simple protocol for transferring files over a link. After some initial negotiation, A sends data packets of size 1 KB to B; B then replies with an acknowledgment. A always waits for each ACK before sending the next data packet; this is known as stop-and-wait. Packets that are overdue are presumed lost and are retransmitted. (a) In the absence of any packet losses or duplications, explain why it is not necessary to include any "sequence number" data in the packet headers. (b) Suppose that the link can lose occasional packets, but that packets that do arrive always arrive in the order sent. Is a 2-bit sequence number (that is, N mod 4) enough for A and B to detect and resend any lost packets? Is a 1-bit sequence number enough? (c) Now suppose that the link can deliver out of order and that sometimes a packet can be delivered as much as 1 minute after subsequent packets. How does this change the sequence number requirements?
Consider a network connecting two systems located 4000 kilometers apart. The bandwidth of the network is 500 x Mbps. The propagation speed of the media is 4 × 106 meters per second. It is needed to design a Go-Back-N sliding window protocol for this network. The average packet size is 107 bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. What is the minimum size in bits of the sequence number field?
1. Consider a path from host A to host B through a router X as follows: A- -X-B The capacity of the link AX is denoted Ra, while the capacity of the link XB is denoted Rb in units of [bits/s]. Assume that Ra Ri. Is it possible that the second packet queues at input queue of the second link? Explain. Now suppose that host A sends the second packet T seconds after sending the first packet. How large must T be to ensure no queueing before the second link? Explain.
hdet b) Consider sending a packet contains 1100 bits from Host A to Host B in a store and forward nerwork. There are 10 links (and 9 routers) between A and B, and the links are congested (there Is a queuing delays). Assume propagation delay over the links are negligible. As a packet travels along the route, it encounters an average of 5 packets already waiting in the queue to be transmitted when it arrives at each router, How long does it take for the packet to get to the receiver if the nodes transmit on a "first come first served" basis (in ms)?
Consider the Go-Back-N (GBN) and Selective Repeat (SR) protocols with a sender window size of 4 and a sequence number range of 1024. For each of these protocols, describe what happens for the following cases: The first packet in the sender window size is lost before reaching the destination. All transmitted packets reached the destination except the third one. Only the first and last packets in the sender window size reached the destination. Only the ACKs of the first and last packets, in the sender window size, reached the destination.
Consider the Go-Back-N (GBN) and Selective Repeat (SR) protocols with a sender window size of 4 and a sequence number range of 1024. For each of these protocols, describe what happens for the following cases:.Only the ACKs of the first and last packets, in the sender window size, reached the destination.
Question 7 Consider the Go-back-N protocol with a sequence number space {0,1,2,3} and a window size N=3, and suppose that the sender wants to send 7 packets in total (excluding retransmissions), where the first packet sent will get sequence number 0. Assume that the 2-nd packet sent by the sender as well as the first ACK with a sequence number of 2 are both lost. All other messages arrive within 1 unit of time, and the sender uses a timeout value of 4 time units before initiating a retransmission. You can assume that the sender sends all packets as soon as possible and we neglect the transmission delay. • List all sequence numbers in the exact order in which they arrive at the receiver. (Note that this includes sequence numbers of packets sent in retransmission.) • What are the values of the send_base and the rcv_base variables after the sender has received the ack for its final packet?
In protocol 6, the code for frame arrival has a section used for NAKs. This section is invoked if the incoming frame is a NAK and another condition is met. Give a scenario where the presence of this other condition is essential.
Consider the Go-Back-N (GBN) and Selective Repeat (SR) protocols with a sender window size of 4 and a sequence number range of 1024. For each of these protocols, describe what happens if only the ACKs of the first and last packets, in the sender window size, reached the destination.