Network and Data Communications · Unit 5
Error Detection and Control
Exam-focused notes for Error Detection and Control (Network and Data Communications, BIT254): what the TU syllabus asks and how it has actually been tested, with 8 solved past questions from this unit.
What this unit covers
- Cyclic Redundancy Check CRC
- CRC polynomial calculation
- CRC transmitted frame encoding
- CRC error checking at receiver
- Stop-and-Wait ARQ design
- Selective Repeat ARQ design
- ARQ flow diagrams
- Reliable and unreliable protocols
- Error detection techniques
CRC transmitted frame encoding
A bit stream 11011001 is transmitted using a standard CRC method. The generator polynomial is $x^3 + x - 1$. Show the actual bit string transmitted and show the error checking on the receiver side. [5]
- Message bit stream (M): 11011001 (8 bits) - Generator polynomial: $x^3 + x - 1$ - In modulo-2 (GF(2)) arithmetic, $-1 \equiv +1$, so $x^3 + x - 1 = x^3 + x + 1$ - Generator (G): 1011 (4 bits, degree $r = 3$) --- $$M' = 11011001 \,\\, 000 = 11011001000$$ S...
Full solved answer →A bit stream 1001100 is transmitted using a standard CRC method. The generator polynomial is $x^3 + 1$. Show the actual bit string transmitted. [5]
- Message $M$ = 1001100 - Generator polynomial: $x^3 + 1$ → 1001 - Degree $r = 3$ Append 3 zeros to the message: $$1001100 \rightarrow 1001100000$$ I carry out the division carefully, XOR-ing whenever the leading bit is 1. Let me do it bit-by-bit with a run...
Full solved answer →Calculate the transmitted encoded frame if the message sequence is 10010001 and generator polynomial is $G(X) = x^2 + x + 1$ [5]
- Message sequence $M = 10010001$ - Generator polynomial $G(X) = x^2 + x + 1$ $G(X) = x^2 + x + 1 \Rightarrow \mathbf{111}$ Degree $r = 2$, so append 2 zeros. $$1001000100$$ Let me perform the division carefully, tracking each bit. I'll process left to righ...
Full solved answer →Error detection techniques
Explain any one error control technique. [5]
Error control refers to the mechanisms used in data communication to detect and correct errors that occur during transmission. One widely used error control technique is ARQ (Automatic Repeat reQuest), and the simplest form of ARQ is Stop-and-Wait ARQ. --- ...
Full solved answer →Reliable and unreliable protocols
Write short notes on Reliable Protocol and Satellite Network [5]
--- A reliable protocol is a communication protocol that guarantees the delivery of data from sender to receiver correctly, completely, and in order. - Error Detection and Correction: Uses checksums, CRC, or parity bits to detect errors in transmitted data....
Full solved answer →Differentiate between reliable and unreliable protocol. Provide example of each. How does protocol check for errors? [5]
A reliable protocol is a communication protocol that guarantees delivery of data from sender to receiver. It ensures that: - Data arrives without errors - Data arrives in order - No data is lost or duplicated - The sender receives an acknowledgement (ACK) f...
Full solved answer →Stop-and-Wait ARQ design
Explain the design of Stop-and-Wait ARQ. Illustrate with suitable flow diagram example[10]
ARQ (Automatic Repeat reQuest) is an error-control mechanism used in data link layer and transport layer protocols. It combines error detection with retransmission to ensure reliable data delivery over an unreliable channel. Stop-and-Wait ARQ is the simples...
Full solved answer →Selective Repeat ARQ design
Explain the design of Selective Repeat ARQ. Illustrate with suitable flow diagram example[10]
Selective Repeat ARQ (Automatic Repeat reQuest) is a sliding window protocol used in data link layer and transport layer for error control. Unlike Go-Back-N ARQ, it retransmits only the erroneous or lost frames, not all subsequent frames. This makes it more...
Full solved answer →Make Unit 5 stick
Practice BIT254 with flashcards & quizzes