cs2005

1. CS2005
Networks and Operating Systems
Exam Brief

2. The Exam
The exam will run as timed, on-campus exams
Lecture notes will be available on WiseFlow
The exam lasts for 3 hours
There are FOUR questions
You MUST attempt ALL FOUR questions
All questions are marked as:
PASS+/PASS/MARGINAL/FAIL

3. Exam questions
Exam questions are short answer and short essay style
There will be:
 One (1) short answer question with 15 parts
 You MUST attempt ALL parts
 Three (3) short essay questions
 You MUST attempt ALL three questions
 How long should an answer be?
 Should you include diagrams?

4. Exam questions
Short answer question
There will be:
 One (1) short answer question with 15 parts
 You MUST attempt ALL parts
 How long should an answer be?
 Few words or a phrase
 Should you include diagrams?
 No
 We will see examples in the next slides

5. Exam questions
Short essay questions
There will be:
 Three (3) short essay questions
 You MUST attempt ALL three questions
 How long should an answer be?
 Roughly 1 to 1.5 pages (approx. 500 – 800 words)
 Should you include diagrams?
 Not necessarily
 We will see examples in the next slides

6. What is expected
It is expected to draw upon your reading and
experience to answer the questions and give
specific examples, with illustrations where
appropriate.

7. What is expected
It is expected to draw upon your
reading (from the course
books) and experience
(practical lab exercises)
to answer the questions and give
specific examples, with illustrations
(diagrams) where appropriate.

8. Marking scheme
 All 4 questions are marked in a 4-grade scale
 PASS+/PASS/MARGINAL/FAIL (P+/P/M/F)
 All 4 questions have equal weight

9. Marking scheme
A PASS+ in one question AND a PASS in three questions is the
threshold for the A band grades.
A PASS+ in one question AND a PASS in two questions is the threshold
for the B band grades.
A PASS+ in one question AND a PASS in one question is the threshold
for the C band grades.
A PASS in one question is the threshold for the D band grades.
A MARGINAL in all 4 questions results in E grade, i.e. attempting but
not quite attaining a PASS.
A FAIL in all 4 questions results in an F grade, i.e. not attempting a
reasonable response.
If you achieve PASS+ in all 4 questions and your answers are
consistently of a very high standard, this will result in an A* grade.

10. Grade matrix
number of
questions passed performance per question
1 2 3 4
4 P+ P+ P+ P+ A+ potential A-star
4 P+ P+ P+ P A
4 P+ P+ P P A
4 P+ P P P A-
4 P P P P B+
3 P+ P+ P+ Mor F B
3 P+ P+ P Mor F B
3 P+ P P Mor F B-
3 P P P Mor F C+
2 P+ P+ Mor F Mor F C
2 P+ P Mor F Mor F C-
2 P P Mor F Mor F D+
1 P+ Mor F Mor F Mor F D
1 P Mor F Mor F Mor F D-
M M M M E+
M M M F E
M M F F E
M F F F E-
F F F F F

11. Approach
 Practice with revision hints and tips (see next slides)
Short answer
 Think specific, key terms
 Manage your time wisely!
 PASS+/PASS/MARGINAL/FAIL depends on how many parts of the question
you have answered correctly
Short essay
 Essay structure is key (think about how you ANSWER THE QUESTION)
 ANSWER THE QUESTION
 Don’t brain dump!
 i.e. spot a keyword in the question and write everything
you know about it rather than answering the question
 PASS+/PASS/MARGINAL/FAIL depends on your ability to
answer the question

12. Topics
 Question 1: Short answer
 Covers all topics and labs
 Questions 2, 3 and 4: Short essay
 Question 2 covers all Networks topics
• Application layer (incl. Distributed Systems)
• Transport layer
• Network layer
 Question 3 covers all Operating Systems topics
• Operating Systems Structures
• Processes
• Threads
• Synchronisation
 Question 4 covers all Security topics
• Security problem (threats and attacks)
• Encryption

13. Revision hints and tips
 Question 1: Short answer – 15 parts
• To pass Q1 you MUST answer at least 8 parts correctly
Example questions:
i. Which two of the OSI model’s layers are NOT included in the TCP/IP
stack?
ii. The Internet Standards are described in formal documents. What
are these documents called?
iii. What is the interface between a process and the network?
iv. Complete the phrase: “The Transport layer provides logical
communication between ____ .“
v. Is a “link state” routing algorithm centralised or decentralised?
vi. Memory can be dynamically allocated to a process during runtime.
What is it called?
vii. Does a thread share its code section with other threads belonging
to the same process?
viii. In which part of its code can a process change shared variables?
ix. Is Trojan Horse an example of program threat?
x. For the screenshot of Wireshark examining HTTP behaviour, what
are the IP address and port number of the client host?

14. Revision hints and tips
 Question 2: Short essay
• Covers all Networks topics (Application layer (incl. Distributed
Systems), Transport layer and Network layer)
Example question:
Answer the question below. Use examples to illustrate your answer:
Q2. Discuss how two processes communicate over a network. Include in your answer the role of
Sockets, Ports, IP Addresses and what is required from Transport Services available to
Applications.
Example question:
Answer the question below. Use examples to illustrate your answer:
Q2. Define Multiplexing and Demultiplexing in the Transport Layer. Discuss how Transport Layer
segments are sent and received in connectionless and connection-oriented protocols.

15. Networks revision topics
 Internet components & services (hosts, protocols, RFCs, IETF, …)
 Protocol layers (OSI, TCP/IP)
 Main principles of network applications (client-server, P2P, message exchange, IP addresses,
sockets, port numbers, data integrity, throughput, …)
 Web services (HTTP, messages, request, response, headers, …)
 Electronic mail over the Internet (user agent, mail server, SMTP, POP3, IMAP, HTTP, …)
 How processes communicate (messages, sockets, port numbers, IP addresses, …)
 Transport services (mux/demux, reliable data transfer, flow control, congestion control, …)
 TCP, UDP
 Segment structure (port #, seq, ack numbers, receive window, …)
 Forwarding/routing
 Routing algorithms
 Router components
 IPv4 & IPv6 datagram
 IPv4 addressing
 Fragmentation / reassembly

16. Revision hints and tips
 Question 3: Short essay
• Covers all Operating Systems topics (Operating Systems Structures,
Processes, Threads and Synchronisation)
Example question:
Answer the question below. Use examples to illustrate your answer:
Q3. What are system programs? What is their purpose and how are they different from
application programmes. Discuss FIVE categories of system programs.
Example question:
Answer the question below. Use examples to illustrate your answer:
Q3. What are the main states of a Java Thread? Discuss the lifecycle of a Java Thread and how it
shares run time with other Threads.

17. Operating Systems revision topics
 Operating systems services
 Operating systems interfaces (users, programs)
 System calls
 System programs
 What is a process (structure, PCB, …)?
 Process states and lifecycle
 Process scheduling (schedulers, queues, …)
 Concurrency / parallelism
 What is a thread?
 Threads states and lifecycle (in Java)
 Critical section problem
 Critical section problem solution requirements
 Bounded buffer (producer-consumer) problem
 Race condition
 Mutex locks, semaphores, monitors
 Deadlock / starvation

18. Revision hints and tips
 Question 4: Short essay
• Covers all Security topics (Security problem (threats and attacks) and
Encryption)
Example question:
Answer the question below. Use examples to illustrate your answer:
Q4. Discuss THREE types of Program Threats. Give an example for each one.
Example question:
Answer the question below. Use examples to illustrate your answer:
Q4. What are accidental or malicious security violations. Discuss FOUR types and THREE levels at
which security measures could be taken.

19. Security revision topics
 Security violations
 Security measures
 Program threats and examples
 System and network threats and examples
 Cryptography terms
 Encryption
 Encryption algorithms essential property
 Symmetric encryption and example algorithms
 Asymmetric encryption and example algorithms

20. Remember
 Revise the textbook sections and slides as indicated in the
lectures
 In your answers
• DO NOT copy from the textbook or any other source
• Draw YOUR OWN diagrams
 Revision lecture in week 32
 Use the BBL Exam Forum to post exam-related questions

21. Textbook references
Computer Networks
 Chapter 1 Computer Networks and the Internet
 1.1 What Is the Internet?
 1.1.1 A Nuts-and-Bolts Description
 1.1.2 A Services Description
 1.1.3 What Is a Protocol?
 1.5 Protocol Layers and Their Service Models
 Chapter 2 Application Layer
 2.1 Principles of Network Applications
 2.2 The Web and HTTP
 2.3 Electronic Mail in the Internet
 2.7 Socket Programming: Creating Network Applications
 Chapter 3 Transport Layer
 3.1 Introduction and Transport-Layer Services
 3.2 Multiplexing and Demultiplexing
 3.3 Connectionless Transport: UDP
 3.5 Connection-Oriented Transport: TCP
 3.7 TCP Congestion Control

22. Textbook references (continued)
Computer Networks (cont.)
 Chapter 4 The Network Layer: Data Plane
 4.1.1 Forwarding and Routing: The Data and Control Planes
 4.2 What’s Inside a Router? (overview and 4.2.1 Input Port Processing and Destination-Based
Forwarding ONLY)
 4.3 The Internet Protocol (IP): IPv4, Addressing, IPv6, and More
 4.3.1 IPv4 Datagram Format
 4.3.2 IPv4 Datagram Fragmentation
 4.3.3 IPv4 Addressing (excluding “Obtaining a block of addresses” & “Obtaining a Host Address: The
Dynamic Host Configuration Protocol”)
 4.3.5 IPv6 (excluding “Transitioning from IPv4 to IPv6”)
 Chapter 5 The Network Layer: Control Plane
 5.2 Routing Algorithms (overview ONLY)

23. Textbook references (continued)
Operating Systems Concepts
 Chapter 2 Operating-System Structures
 2.1 Operating-System Services
 2.2 User and Operating-System Interface
 2.3 System Calls
 2.4 Types of System Calls
 2.5 System Programs
 Chapter 3 Processes
 3.1 Process Concept
 3.2 Process Scheduling
 3.6.2 Remote Procedure Calls
 3.6.3 Pipes
 Chapter 4 Threads
 4.1 Overview
 My slides and links: Java Threads

24. Textbook references (continued)
Operating Systems Concepts (cont.)
 Chapter 5 Process Synchronization
 5.1 Background
 5.2 The Critical-Section Problem
 5.3 Peterson’s Solution
 5.5 Mutex Locks
 5.6 Semaphores
 5.7 Classic Problems of Synchronisation
 5.8 Monitors
 Chapter 15 Security
 15.1 The Security Problem
 15.2 Program Threats
 15.3 System and Network Threats
 15.4.1 Encryption
 Chapter 17 Distributed Systems
 17.1 Advantages of Distributed Systems

25. AND