The University of Nottingham

SCHOOL OF COMPUTER SCIENCE

A LEVEL 4 MODULE, AUTUMN SEMESTER 2017-2018

SYSTEMS AND NETWORKS

Time allowed 2 Hours

Candidates may complete the front cover of their answer book and sign their desk card but must NOT write anything else until the start of the examination period is announced

Answer 3 out of 5 questions

Only silent, self contained calculators with a Single-Line Display or Dual-Line Display are permitted in this examination.

Dictionaries are not allowed with one exception. Those whose first language is not English may use a standard translation dictionary to translate between that language and English provided that neither language is the subject of this examination. Subject specific translation dictionaries are not permitted.

No electronic devices capable of storing and retrieving text, including electronic dictionaries, may be used.

DO NOT turn examination paper over until instructed to do so

ADDITIONAL MATERIAL: None

INFORMATION FOR INVIGILATORS: None

Question 1: Unix

[overall 25 marks]

a. Write UNIX commands to do the following:

i.   Copy the file data1.txt to the file called data2.txt

ii.   Rename the file data2.txt to be called logdata.txt

iii.  Do a listing of the current directory and append the results to the file logdata.txt

[6 Marks]

b. Examine the following UNIX command:

who | grep severn

i.   Adapt the given command so that the result of the command is sorted into alphabetical order and displayed in the shell

ii.   Adapt the given command so that the result of the command is stored in a new file called users.txt

iii.  Adapt the given command so that the result of the command is stored in a file called users.txt but any errors are stored in a file called errors.txt

[6 Marks]

c. Explain, using an example of each, the difference between shell metacharacters and regular expressions.

[3 Marks]

d. Under what circumstances would you need to use quotes with grep? Why?

[2 Marks]

e. grep and echo can be used with either single or double quotes. Explain, with an example, when you should use single quotes and when you should use double quotes and why.

[4 Marks]

f. UNIX has a number of different signals. Explain the role of a UNIX signal and give an example of how a UNIX signal might be generated.

[4 Marks]

Question 2: Local Area Networks

[overall 25 marks]

a. Describe one form of multiplexing that you might find on a twisted pair copper transmission cable.

[4 Marks]

b. What is the main problem with twisted pair cables? Give TWO solutions to the problem you have identified.

[3 Marks]

c. Why are wires twisted together in twisted pair copper cables? Can you have more than one pair of wires in a cable and if so, how?

[5 Marks]

d. Describe TWO technologies that are commonly used to extend LANs.

[4 Marks]

e. Do you think that extending a LAN using one of the technologies described in your answer to section d. above will make it a WAN? Explain your answer.

[4 Marks]

f. Describe the mechanism used by Ethernet wired LAN hosts in order to gain access to the shared medium.

[5 Marks]

Question 3: Wide Area Networks

[overall 25 marks]

a. Describe the journey that an IPV4 packet takes from a sender to a receiver in terms of the following:

i.   How the packet is packaged into a frame by the sender and the information that is added

[4 Marks]

ii.  What the router does to the frame between the time it receives it and the time it forwards it on

[4 Marks]

iii.  What information the router uses to route the frame and how it does this

[4 Marks]

b. What error reporting mechanism does IP use and how does it work?

[3 Marks]

c. Explain the role of DHCP and describe how it works.

[6 Marks]

d. Why does DHCP operate a leasing scheme? Explain the circumstances under which a DHCP lease would expire.

[4 Marks]

Question 4: Distributed Applications

[overall 25 marks]

a. Describe the steps in communication that occur in a typical FTP session between client and server.

[8 Marks]

b. FTP clients operate at layer 5 of the TCP/IP protocol stack. Which layer 4 protocol do you think would be used by an FTP client to send its data and why?

[4 Marks]

c. With respect to distributed network systems, briefly explain what a Directory Service is.

[1 Mark]

d. Draw a diagram to show the process of iterative and recursive queries in DNS. Under what circumstances would each type of query be used?

[6 Marks]

e. Briefly describe THREE types of service that are offered by Cloud computing technologies and give an example of each.

[6 Marks]

Question 5: Disks and Filesystems

[overall 25 marks]

a. Draw a diagram of an inode and explain how it is used in filesystems to locate files on a disk.

[6 Marks]

b. Explain the purpose of RAID arrays and describe TWO mechanisms that RAID arrays use to achieve this purpose. Use diagrams to illustrate your answer.

[8 Marks]

c. Filesystems can be distributed across a network. Give ONE example of a shared filesystem and explain its purpose relative to the operating systems involved.

[4 Marks]

d. What is a file handle?

[1 Mark]

e. A user sits down to work at their PC and each time they do this they hear a “chugging” noise coming from the hard drive. Explain, with a diagram, what you think the problem is and how the user might solve it.

[6 Marks]