R5. Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC channel? Why or why not? 6. List the available residential access technologies in your city. For each type of access, provide the advertised downstream rate, upstream rate, and monthly price. R11. Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R, and R2, respec- tively. Assuming that the switch uses store-and-forward packet switching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing, propagation delay, and processing delay.) network? Suppose users share a 2 Mbps link. Also suppose each user transmits continu- ously at 1 Mbps when transmitting, but each user transmits only 20 percent of the time. (See the discussion of statistical multiplexing in Section 1.3.) R13, HOMEWORK PROBLEMS AND QUESTIONS a. When circuit switching is used, how many users can be supported? b. For the remainder of this problem, suppose packet switching is used. Why will there be essentially no queuing delay before the link if two or fewer users transmit at the same time? Why will there be a queuing delay if three users transmit at the same time? c. Find the probability that a given user is transmitting. d. Suppose now there are three users. Find the probability that at any given time, all three users are transmitting simultaneously. Find the fraction of time during which the queue grows. R18. How long does it take a packet of length 1,000 bytes to propagate over a link of distance 2,500 km, propagation speed 2.5 108 m/s, and transmission rate 2 Mbps? More generally, how long does it take a packet of length L to propa- gate over a link of distance d, propagation speed s, and transmission rate R bps? Does this delay depend on packet length? Does this delay depend on transmission rate? R24. What is an application-layer message? A transport-layer segment? A network- layer datagram? A link-layer frame? R26. What is the difference between a virus and a worm? P6. This elementary problem begins to explore propagation delay and transmis- sion delay, two central concepts in data networking. Consider two hosts, A and B, connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters, and suppose the propagation speed along the link is s meters/sec. Host A is to send a packet of size L bits to Host B. a. Express the propagation delay, aprop in terms of m and s. b. Determine the transmission time of the packet, dirans, in terms of L and R. c. Ignoring processing and queuing delays, obtain an expression for the end- d. Suppose Host A begins to transmit the packet at time t 0. At time t dns e. Suppose d gop is greater than dmn, At time r - dras where is the first bit of f. Suppose dprop is less than drans At timer - dram, where is the first bit of g. Suppose s 2.5.108, L 120 bits, and R-56 kbps. Find the distance m to-end delay. where is the last bit of the packet? the packet? the packet? so that d pop equals drans P7. In this problem, we consider sendin P24. Suppose you would like to urgently deliver 40 terabytes data from Boston to Los Angeles. You have available a 100 Mbps dedicated link for data transfer. Would you prefer to transmit the data via this link or instead use FedEx over- night delivery? Explain