Consider a short, 10-meter link, over which a sender can transmit at a rate of 150 bits/sec in both directions. Suppose that packets containing data are 100,000 bits long, and packets containing only control (e.g., ACK or handshaking) are 200 bits long. Assume that N parallel connections each get 1/N of the link bandwidth. Now consider the HTTP protocol, and suppose that each downloaded object is 100 Kbits long, and that the initial downloaded object contains 10 referenced objects from the same sender. Would parallel downloads via parallel instances of non-persistent HTTP make sense in this

Consider a short, 10-meter link, over which a sender can transmit at a rate of 150 bits/sec in both directions. Suppose that packets containing data are 100,000 bits long, and packets containing only control (e.g., ACK or handshaking) are 200 bits long. Assume that N parallel connections each get 1/N of the link bandwidth. Now consider the HTTP protocol, and suppose that each downloaded object is 100 Kbits long, and that the initial downloaded object contains 10 referenced objects from the same sender. Would parallel downloads via parallel instances of non-persistent HTTP make sense in this

Systems Architecture

7th Edition

ISBN:9781305080195

Author:Stephen D. Burd

Publisher:Stephen D. Burd

Chapter13: Internet And Distributed Application Services

Section: Chapter Questions

Problem 15VE

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Consider a short, 10-meter link, over which a sender can transmit at a rate of 150 bits/sec in both directions. Suppose that packets containing data are 100,000 bits long, and packets containing only control (e.g., ACK or handshaking) are 200 bits long. Assume that N parallel connections each get 1/N of the link bandwidth. Now consider the HTTP protocol, and suppose that each downloaded object is 100 Kbits long, and that the initial downloaded object contains 10 referenced objects from the same sender. Would parallel downloads via parallel instances of non-persistent HTTP make sense in this case? Now consider persistent HTTP. Do you expect significant gains over the non-persistent case? Justify and explain your answer
Consider sending a file of F bits over a path of Q links. Each link transmits at R bits per second (bps). The network is lightly loaded so that there are no queueing delays. When a form of packet switching is used, the F bits are broken up into packets, each packet with L bits, of which h bits of it are header. Propagation delay is negligible. Let F = 5x104, Q = 20, R = 1 Mbps, L = 1000, and h = 10. c. Suppose the network is a packet-switched virtual circuit network. Denote the VC set-up time by ts = 250 milliseconds. How long does it take to send the file from source to destination?
Consider sending a file of F bits over a path of Q links. Each link transmits at R bits per second (bps). The network is lightly loaded so that there are no queueing delays. When a form of packet switching is used, the F bits are broken up into packets, each packet with L bits, of which h bits of it are header. Propagation delay is negligible. Let F = 5x104, Q = 20, R = 1 Mbps, L = 1000, and h = 10. b) Suppose the network is a packet-switched datagram network and a connectionless service is used. How long does it take to send the file?
Consider an HTTP server and client as shown in the figure below. Suppose that the RTT delay between the client and server is 13 msecs; the time a server needs to transmit an object into its outgoing link is 1 msecs. Any other HTTP message not containing an object has a negligible (zero) transmission time. Suppose the client again makes 106 requests, one after the other, waiting for a reply to a request before sending the next request. Assume the client is using HTTP 1.1 and the IF-MODIFIED-SINCE header line. Assume 47% of the objects requested have NOT changed since the client downloaded them (before these 106 downloads are performed). Clients RTT delay: t Transmission delay: ta Intemet APACHE Server How much time elapses (in milliseconds) between the client transmitting the first request, and the completion of the last request?
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?
In a bit-oriented link-layer protocol, the start and end of a frame are each marked by a flag, which is a sequence of exactly 6 consecutive 1 bits. Bit stuffing is used during the rest of the frame: after sending 5 consecutive 1 bits, a 0 is added. The bits below contain an example frame, with the leftmost bit received first. The content of the frame is a sequence of bytes, sent most significant bit first. Put the values of the first four bytes of the frame content, in order, in the four answer boxes below. You may enter the values in either decimal (e.g. 76, 123) or hexadecimal (e.g. 2a, f7). 00101011111010001111110011100111110000111101111101010110100010010011111101101100100 57−240−123−229
In protocol rdt3.0, the ACK packets flowing from the receiver to the sender do not have sequence numbers, although they do have an ACK field that contains the sequence number of the packet they are acknowledging. Why is it that ACK packets do not themselves require sequence numbers?
It is possible for a series of packets to be sent from one host to another over the same connection. Please break down the time it takes for a single package to go from beginning to conclusion. Is it expected that one of the delays would last a certain period of time while the other delay's length will be more malleable?
A link between two hosts may carry many packets at once. Please give a timetable outlining all the tasks that must be completed to complete one shipment. Is it expected that one of the delays would take a fixed period of time, while the other delay's length may be modified as needed?
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?
A link between two hosts may carry many packets at once. Give me a breakdown of how long each stage of processing a cargo takes. Does one delay's length have to be fixed, while the other's may vary depending on the circumstances?
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.