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 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.

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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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
Suppose that the average object size is 850,000 bits and that the average request rate from the institution’s browsers to the origin servers is 16 requests per second. Also suppose that the amount of time it takes from when the router on the Internet side of the access link forwards an HTTP request until it receives the response is three seconds on average (see Section 2.2.5). Model the total average response time as the sum of the average access delay (that is, the delay from Internet router to institution router) and the average Internet delay. For the average access delay, use Δ/(1 – Δ ), where Δ is the average time required to send an object over the access link and is the arrival rate of objects to the access link. a. Find the total average response time.b. Now suppose a cache installed in the institutional LAN, Suppose the miss rate is 0.4. Find the total response time.
Consider Figure 2.12, for which there is an institutional network connected to the Internet. Suppose that the average object size is 1,000,000 bits and that the average request rate from the institution’s browsers to the origin servers is 16 requests per second. Also suppose that the amount of time it takes from when the router on the Internet side of the access link forwards an HTTP request until it receives the response is three seconds on average (see Section 2.2.5). Model the total average response time as the sum of the average access delay (that is, the delay from Internet router to institution router) and the average Internet delay. For the average access delay, use ∆/(1 - ∆b), where ∆ is the average time required to send an object over the access link and b is the arrival rate of objects to the access link. Find the total average response time. I get ∆=1000000/15000000= 1/15, then ∆/(1 - ∆b)= (1/15)/(1-(1/15)*16)=-1, so the finally answer is : 3+(-1)=2s or 3+0=3s?
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 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
Suppose we have a web page which contains 10 objects including: a html main file, 8 jpg image, and a .mp3 background music. For simplicity, assume each of the 10 objects has a size of 4 Kbits and that each object can be completely transferred in one TCP packet. Furthermore, assume the round-trip time between the server and client is RTT= 250 ms, and the download rate is 1 Mbps. What will be the time it takes to complete transferring the web page running in the non-persistent mode? Total delay = ms
In this problem, we consider sending real-time voice from Host A to Host B over a packet switched network (VoIP). Host A converts analog voice to a digital 64 kbps bit stream on the fly. Host A then groups the bits into 56-byte packets. There is one link between Hosts A and B; its transmission rate is 2 Mbps and its propagation delay is 10 msec. As soon as Host A gathers a packet, it sends it to Host B. As soon as Host B receives an entire packet, it converts the packet's bits to an analog signal. How much time elapses from the time a bit is created (from the original analog signal at Host A) until the bit is decoded (as part of the analog signal at Host B)?
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?
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?
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?
In modern packet-switched networks, including the Internet, the source host segments long, application-layer messages (for example, an image or a music file) into smaller packets and sends the packets into the network. The receiver then reassembles the packets back into the original message. We refer to this process as message segmentation. Figure 1.27 illustrates the end-to-end transport of a message with and without message segmentation. Consider a message that is 8. 106 bits long that is to be sent from source to destination in Figure 1.27. Suppose each link in the figure is 2 Mbps. Ignore propagation, queuing, and processing delays. a. Consider sending the message from source to destination without message segmentation. How long does it take to move the message from the source host to the first packet switch? Keeping in mind that each switch uses store-and-forward packet switching, what is the total time to move the message from source host to destination host? b. Now suppose that…