BSc. (Hons) Web Technologies. Examinations for 2017 / Semester 1

Transcription

1 BSc. (Hons) Web Technologies Cohort: BWT/17A/FT Examinations for 2017 / Semester 1 MODULE: NETWORK ESSENTIALS MODULE CODE: CAN 1104C Duration: 2 ½ hours Instructions to Candidates: 1. Answer ALL 4 (four) questions. 2. Questions may be answered in any order but your answers must show the question number clearly. 3. Always start a new question on a fresh page. 4. All questions carry equal marks. 5. Total marks 100. This question paper contains 4 questions and 9 pages. Page 1 of 8

2 ANSWER ALL 4 (FOUR) QUESTIONS QUESTION 1: (25 MARKS) a) Briefly describe what a network is. (3 marks) b) What is a physical topology? Briefly illustrate four types of topology. (1 + 4 marks) c) Differentiate between a LAN, MAN and WAN. In which category would you classify the UTM network? Why? ( marks) d) Illustrate and briefly describe each layer of the TCP/IP model. State the names of the packets at each of the top four layers. (6 + 2 marks) e) Consider table 1.1 which depicts various applications and their properties. Table 1.1: Selected applications and their properties i) What does the term elastic mean in the context of table 1.1? ii) Why are the first three applications non time-sensitive? iii) Real time audio/video is said to be loss tolerant. What does that imply with regard to packet transmission? Page 2 of 8

3 iv) Which layer four protocol would you prefer for real-time audio/video? ( marks) QUESTION 2: (25 MARKS) a) HTTP is said to use port 80. Briefly explain the use of ports when a web client is communicating with a web server. (3 marks) b) The response time of an HTTP session is 2 x RTT + transmit time. What does RTT stands? Briefly explain its importance. (1 + 2 marks) c) Differentiate between persistent HTTP and non-persistent HTTP. (4 marks) d) Further explain the advantage of using persistent HTTP with pipelining (2 marks) e) Briefly the importance of cookies to keep client information on the server side. (2 marks) f) What are web caches used for? Briefly explain how conditional GETs are used when caches communicate with their origin servers. (2 + 2 marks) g) Which protocol is used to transfer mail between mail servers? Briefly explain the procedure and specify the two protocols that can be used to fetch the from the recipient mail server? ( marks) Page 3 of 8

4 QUESTION 3: (25 MARKS) a) Differentiate among local name servers, authoritative name servers and root name servers. (6 marks) b) Assuming that the site does not use https, and that with some knowledge of networking, a student decides to telnet to the site. He does so by typing telnet 80 in a DOS prompt. What happens when the student types that line? (1 mark) c) Suppose the student continues from b) and type the following lines of code: HEAD / HTTP/1.1 (presses enter once) host: (presses enter twice) and gets a server response as shown in Fig 3.1 Fig 3.1: Server response for the website Page 4 of 8

5 i) What does the line HTTP/ OK mean? ii) What does the line connection: keep-alive mean? iii) If instead of writing HEAD HTTP/1.1, the student had typed GET / HTTP/1.1, how would the server response been different? ( marks) d) Assuming that another student who learned some networking basics types the following code in a DOS prompt: ipconfig /all and gets a reply as specified in Fig 3.2. Fig 3.2: Response to ipconfig /all command i) What is the IPv4 address of the client machine? ii) What does the term DHCP Enabled mean? ii) What is the meaning of the line Lease Expires? ( marks) e) Assume the student goes one additional step and types the following command: ping Page 5 of 8

6 and obtains the response as shown in Fig 3.3. Fig 3.3: Response to ping command i) What is the IP address of ii) By making use of Fig 3.2, deduce the IP address of the DNS server where the IP address of was fetched? iii) What does the term TTL stand for? What does it mean? ( marks) f) If the student wanted to know the number of routers that lie between his network and which command should he/she type? How would the response be different if the student used instead? (2 + 2 marks) g) TCP provides a reliable service to HTTP. What does that mean? (2 marks) Page 6 of 8

7 QUESTION 4: (25 MARKS) a) Consider Fig 4.1 which depicts the communication between client and server for UDP and TCP. a) b) Fig 4.1: Communication between client processes and server process(es) for a) UDP and b) TCP i) What does a TCP socket consists of? ii) What does a UDP socket consists of? iii) Use Fig 4.1 as support to explain the difference between TCP processes and UDP processes. ( marks) Page 7 of 8

8 b) To open a TCP connection, a three-way handshake is required. Briefly describe the three steps of this procedure. (6 marks) c) Describe the difference between routing and forwarding used in routers. (4 marks) d) One problem faced by the IP layer is fragmentation. Consider Fig 4.2 which depicts such a fragmentation. (a) (b) Fig 4.2: a) IP packet with size 4000 bytes that needs to be carried over a link with MTU 1500 bytes, b) the first fragmented packet i) Briefly explain why IP fragmentation occurs. ii) Specify the ID of the first fragmented IP packet (2 marks) (1 mark) iii) Specify the length, ID, fragflag and offset values of the remaining fragmented packets. (6 marks) ***END OF QUESTION PAPER*** Page 8 of 8