Data-link Protocols and Error Detection - Computer Networks - Computer Science & Information Technology Previous Year Questions

The message 11001001 is to be transmitted using the CRC polynomial x³+1 to protect it from errors. The message that should be transmitted is:

Let G(x) be the generator polynomial used for CRC checking. What is the condition that should be satisfied by G(x) to detect odd number of bits in error ?

What is the minimum number of bits (l) that will be required to represent the sequence numbers distinctly ? Assume that no time gap needs to be given between transmission of two frames.

Suppose that the sliding window protocol is used with the sender window size of 2^l, where l is the number of bits identified in the earlier part and acknowledgements are always piggy backed. After sending 2^l frames, what is the minimum time the sender will have to wait before starting transmission of the next frame ? (Identify the closest choice ignoring the frame processing time.)

Consider a token ring network with a length of 2 km having 10 stations including a monitoring station. The propagation speed of the signal is \(2 \times 10^8\) m/s and the token transmission time is ignored. If each station is allowed to hold the token for 2 μsec, the minimum time for which the monitoring station should wait (in μsec) before assuming that the token is lost is __________.

Consider a selective repeat sliding window protocol that uses a frame size of 1 KB to send data on a 1.5 Mbps link with a one-way latency of 50 msec. To achieve a link utilization of 60%, the minimum number of bits required to represent the sequence number field is __________.

A bit-stuffing based framing protocol uses an 8-bit delimiter pattern of 01111110. If the output bit-string after stuffing is 01111100101, then the input bit-string is

A sender uses the Stop-and-Wait ARQ protocol for reliable transmission of frames. Frames are of size 1000 bytes and the transmission rate at the sender is 80 Kbps (1Kbps = 1000 bits/second). Size of an acknowledgement is 100 bytes and the transmission rate at the receiver is 8 Kbps. The one-way propagation delay is 100 milliseconds.

Assuming no frame is lost, the sender throughput is __________ bytes/second.

Consider a binary code that consists of only four valid codewords as given below:
00000, 01011, 10101, 11110
Let the minimum Hamming distance of the code be \( p \) and the maximum number of erroneous bits that can be corrected by the code be \( q \). Then the values of \( p \) and \( q \) are

Consider a simple communication system where multiple nodes are connected by a shared broadcast medium (like Ethernet or wireless). The nodes in the system use the following carrier-sense based medium access protocol. A node that receives a packet to transmit will carrier-sense the medium for 5 units of time. If the node does not detect any other transmission in this duration, it starts transmitting its packet in the next time unit. If the node detects another transmission, it waits until this other transmission finishes, and then begins to carrier-sense for 5 time units again. Once they start to transmit, nodes do not perform any collision detection and continue transmission even if a collision occurs. All transmissions last for 20 units of time. Assume that the transmission signal travels at the speed of 10 meters per unit time in the medium.
Assume that the system has two nodes P and Q, located at a distance \( d \) meters from each other. P starts transmitting a packet at time \( t=0 \) after successfully completing its carrier-sense phase. Node Q has a packet to transmit at time \( t=0 \) and begins to carrier-sense the medium.
The maximum distance \( d \) (in meters, rounded to the closest integer) that allows Q to successfully avoid a collision between its proposed transmission and P’s ongoing transmission is ______.

Consider the sliding window flow-control protocol operating between a sender and a receiver over a full-duplex error-free link. Assume the following:
• The time taken for processing the data frame by the receiver is negligible.
• The time taken for processing the acknowledgement frame by the sender is negligible.
• The sender has infinite number of frames available for transmission.
• The size of the data frame is 2,000 bits and the size of the acknowledgement frame is 10 bits.
• The link data rate in each direction is 1 Mbps (= 10⁶ bits per second).
• One way propagation delay of the link is 100 milliseconds.

The minimum value of the sender’s window size in terms of the number of frames, (rounded to the nearest integer) needed to achieve a link utilization of 50% is __________

Consider the following two statements.
\( S_1 : \) Destination MAC address of an ARP reply is a broadcast address.
\( S_2 : \) Destination MAC address of an ARP request is a broadcast address.
Which one of the following choices is correct?

Consider the cyclic redundancy check (CRC) based error detecting scheme having the generator polynomial \(X^3+X+1\). Suppose the message \(m_4m_3m_2m_1m_0 = 11000\) is to be transmitted. Check bits \(c_2c_1c_0\) are appended at the end of the message by the transmitter using the above CRC scheme. The transmitted bit string is denoted by \(m_4m_3m_2m_1m_0c_2c_1c_0\). The value of the checkbit sequence \(c_2c_1c_0\) is

Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is 1 Mbps (= 10^6 bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmissions due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per second. Throughput is defined as the average number of frames successfully transmitted per second. The throughput of the network (rounded to the nearest integer) is __________