Daffodil International University
Department of Computer Science and Engineering
Faculty of Science & Information Technology
Final Exam Examination, Summer 2020 @ DIU Blended Learning Center Course Code: CSE233 (Day), Course Title: Data Communication
Level: 2 Term: 3 Section: O1, O2 Instructor: FZA Modality: Open Book Exam Date: Tuesday 25 August 2020, Time: 02:00pm-06:00pm
Four hours (4:00) to support online open/case study based assessment Marks: 40 Directions:
Students need to go through the CASE STUDY shown in this exam paper.
Analyze and answer specific section based on your own thinking and work.
Do not share as this will be treated as plagiarism by Blended Learning Center.
Use Case-1 A company has two locations: a headquarters and a factory about 25 km away. The factory has four 300-bps terminals that communicate with the central computer facilities over leased voice-grade lines. The company is considering installing TDM equipment so that only one line will be needed.
Mark s
Question-1(a) Draw a block diagram of above case study for a TDM PCM system that will accommodate four 300-bps, synchronous, digital inputs and one analog input with a bandwidth of 500 Hz. Assume that the analog samples will be encoded into 4-bit PCM words.
5
Question-1(b) What cost factors should be considered in the decision? Consider a transmission system using frequency-division multiplexing. What cost
factors are involved in adding one more pair of stations to the system?
5
Question-1(c) Explain in terms of data link control and physical layer concepts how error and flow control are accomplished in synchronous time-division multiplexing.
5
Use Case-2 Suppose you want to send last three digits of your id to your friend. You want to use liner block coding technique on it for error detecting and correcting.
Assume your id is 191-15-24753 you have to send 753. Here data words are of two bits and code words are of five bits.
Marks
Question-2(a) Using the code in Table-1, what would be the data word and code word in your side?
If you friend received 1010111010111100100011001. Find out the received code word and data word to your friend side. Discuss the procedure of detecting and correcting error for this case.
Table-1
7
Question-2(b) Assume that You send a message of 8 characters “GOODLUCK" to 8 Data Word Code Word
00 00000
01 01011
10 10101
11 11110
your friend. You add checksum with the data for detecting error. For calculating checksum the text needs to be divided into 2-byte (l6-bit) words. ASCII code of A-Z is (Ox41 - Ox5A). You have to change each byte to a 2-digit hexadecimal number. For example, G is represented as Ox47 and O is represented as Ox4F. Convert the message to Hexadecimal ASCII code and find out
I. Checksum at the sender site.
II. Checksum at the receiver site if there is no error.
Use Case-3 In controlled access, the stations consult one another to find which station has the right to send. A station cannot send unless it has been authorized by other stations.
Question-3(a) A network with one primary and four secondary stations uses polling.
The size of a data frame is 1000 bytes. The size of the poll, ACK, and NAK frames are 32 bytes each. Each station has 5 frames to send.
How many total bytes are exchanged if there is no limitation on the number of frames a station can send in response to a poll?
5
Question-3(b) How are controlled access protocols different from random access
protocols? 5
