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WEEK 1 Tutorial
Networking Fundamentals (41092)
University of Technology Sydney
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Week 1. Tutorial Problems
R11-extended. 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 R1 and R2, respectively. 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.)
Transmission delay from host to switch = L/R Transmission delay from switch to receiver = L/R L = packet length So, total transmission delay = L/R1 + L/R2 and the total end-to-end delay will also be (L/R1)+(L/R2).
a. Now assume packet length L=1500 byte, R1=1Mbps, R2=2Mbps, calculate the end- to-end Delay.
1 BYTE = 8 MBPS 41092 Network Fundamentals Week 1. Tutorial Problems 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 R1 and R2, respectively. 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.) a. Now assume packet length L=1500 byte, R1=1Mbps, R2=2Mbps, calculate the end- to-end Delay. b. Now assume packet length L=1200 byte, R1=3Mbps, R2=2Mbps, calculate the end- to-end Delay. a) DELAY FORMULA = L / R1 then L / R 1 BYTE = 8 MBPS THEREFORE a) 1500 41092 Network Fundamentals Week 1. Tutorial Problems 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 R1 and R2, respectively. 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.) a. Now assume packet length L=1500 byte, R1=1Mbps, R2=2Mbps, calculate the end- to-end Delay. b. Now assume packet length L=1200 byte, R1=3Mbps, R2=2Mbps, calculate the end- to-end Delay. a) DELAY FORMULA = L / R1 then L / R
1 BYTE = 8 MBPS
THEREFORE a) 1500 15008 / 1,000,000 + 15008 / 2,000,000 = 0 = 18ms
DELAY FORMULA = L /
R1 then L / R
1 BYTE = 8 MBPS
THEREFORE a) 1500*8 /
1,000,000 + 1500*8 /
2,000,000 = 0 =
18ms
b. Now assume packet length L=1200 byte, R1=3Mbps, R2=2Mbps, calculate the end- to-end Delay. 12008 / 3,000,000 + 12008 / 2,000,000 = 0 + 0 = 0 = 8ms
P2. Equation 1.
gives a formula for the end-to-end delay of sending one packet of length L over N links of transmission rate R. Generalize this formula for sending P such packets back-to-back over the N links. N*(L/R) + (P-1)*(L/R)
P3. Consider an application that transmits data at a steady rate (for example, the sender generates an N-bit unit of data every k time units, where k is small and fixed). Also, when such an application starts, it will continue running for a relatively long period of time. Answer the following questions, briefly justifying your answer: a. Would a packet-switched network or a circuit-switched network be more appropriate for this application? Why? A circuit-switched network. because the application involves long sessions with predictable smooth bandwidth requirements. Since the transmission rate is known and not bursty, bandwidth can be reserved for each application session without significant waste
Given such generous
link capacities, the
network does not need
congestion control
mechanisms.
In the worst case, all the applications simultaneously transmit over one or more network links. However, since each link has sufficient bandwidth to handle the sum of all of the applications' data rates, no congestion (very little queuing) will occur. Given such generous link capacities, the network does not need congestion control mechanisms.
P8. Suppose users share a 10 Mbps link. Also suppose each user requires 200 kbps when transmitting, but each user transmits only 10 percent of the time. (See the discussion of packet switching versus circuit switching in Section 1.) a. When circuit switching is used, how many users can be supported? 20 users b. For the remainder of this problem, suppose packet switching is used. Find the probability that a given user is transmitting. P = 0. c. Suppose there are 120 users. Find the probability that at any given time, exactly n users are transmitting simultaneously. (Hint: Use the binomial distribution.)
WEEK 1 Tutorial
Course: Networking Fundamentals (41092)
University: University of Technology Sydney
