exercises networking

8/13/2019 Exercises Networking

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1. Answer True or False for the following statements.a. In general, the higher the frequency used, the higher the

potential bandwidth and therefore the higher the potential data

rate.

b. The higher the data rate, the more cost-effective is thetransmission facility.

c. If the data rate of a digital signal is N bps, then a very goodrepresentation can be achieved with the bandwidth of N/2 Hz.

d. When the bit length of the link is greater than the frame length,multiple frames cannot be in transit at one time.

e. An Internet router connecting N subnetworks requires N-1 IPaddresses.

f. Ethernet is a LAN so it is placed in the second layer of the OSIreference model.

g. UDP provides connectionless service and delivers packetsquickly. In case of packet loss, UDP does not provide

retransmission.

h. DNS is used to translate a host name to its MAC address.i. UDP is the preferred over TCP for transferring a real-time voice

over IP networks.

j. If a digital transmission system has a bit rate of 45megabits/second, then it can carry 1500 PCM voice channels by

the system.

k. Circuit switching networks require signaling and control forestablishing circuits.

l. Framing is required in frequency division multiplexing.


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m.T-1 carrier carries Digital Signal 1 (DS-1) that combines 24voice channels into a digital stream.

n. One of the ways to reduce transmission delay is to use a higher-speed transmission system.o. Jitter is one of the modern sampling techniques for producing

high-quality voice.

p. Bit Error Rate (BER) increases with decreasing signal-to-noiseratio.

2. Choose an appropriate header (A-D) for each protocol below so thatthe headers in the packet shown below will be in the correct order. A B C D Application data CRC

a. HTTP headerb. IP headerc. Ethernet headerd. TCP header

3. A group of N stations shares a 56-kbps ALOHA channel. Each stationoutputs a 1000-bit frame on an average of once every 100 sec.Assuming that the system can achieve its maximum throughput whatmaximum number of stations can be supported?


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4. The following questions deal with CRC error detecting code.a. Given a message M = 1010001101, determine the CRC using the

polynomial P=x5+x4+ x2+ 1. Show your work.

b. What is the transmitted message T?c. How does the receiver check whether the message T wastransmitted without any errors?

5. Suppose a user has two browser applications active at the same time,and suppose that the two applications are accessing the same server to

retrieve HTTP documents at the same time. How does the server tell

the difference between the two applications?

6. Suppose a computer is moved from one building to another within acampus. Does the physical address need to change? Does the IP

address need to change? Does it make a difference if the computer is a

laptop?

7. The following questions deal with broadcasting protocols used inLANs.

a. What is the main difference between the Aloha protocols andCSMA protocols?

b. What is the main difference between the CSMA andCSMA/CD protocols?

c. When is the binary exponential backoff algorithm used in theCSMA/CD LANs? Briefly explain how it works.

8. Answer the following:(a)Identify the address class of the following IP addresses.

200.58.20.165

128.167.23.20

16.196.128.50

(b)Describe what each of the following providesi. DNS

ii. NAT


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Problem 1

A small university campus is assigned a large address block 12.1.0.0/17, but

is only using a portion of these addresses (in 12.1.1.0/24) to number its

computers. The campus uses a single Internet Service Provider (ISP) to

reach the rest of the Internet. This picture shows the forwarding tables on

the ISPs router (on the left) and the campus edge router (on the right):

For example, the ISP forwards all packets with destination addresses in

12.1.0.0/17 out link #2 toward the campus edge router. Both routers include

a default forwarding entry 0.0.0.0/0 that can match any destination IP

address.

1. How many IP addresses does the campus own in its 12.1.0.0/17block? You can represent your answer as a power of two.

2. What are the smallest and largest IP addresses that the campusowns, whether or not the campus is currently using the address?

3. Suppose the ISP router receives a packet with destination IP address12.1.1.1? What path does this packet follow?

4. Suppose the ISP router receives a packet with destination IP address12.1.20.1? What path does this packet follow?

5.What ultimately happens to a packet with destination IP address12.1.20.1? Where does it go?


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Problem 2

Consider the following routing table of a router R.

Destination Network Outgoing Link Interface

196.80.0.0/12 1

196.94.16.0/20 2196.96.0.0/12 3

196.104.0.0/14 4128.0.0.0/1 5

64.0.0.0/2 6

Suppose packets with the following destination IP addresses arrive at the

router R. Find the outgoing link interfaces for forwarding each of these

packets.

1. 176.94.16.02. 96.94.19.1353. 196.94.32.1284. 196.100.100.1005. 196.105.100.18

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