GATE CS Data Link Layer: Framing, Error Detection, MAC, Ethernet Bridging questions

Consider the transmission of data bits $110001011$ over a link that uses Cyclic Redundancy Check (CRC) code for error detection. If the generator bit pattern is given to be $1001$, which one of the following options shows the remainder bit pattern appended to the data bits before transmission?

It is necessary to design a link-layer protocol between two hosts that are directly connected over a lossless link of length $3000$ kilometers. Assume that the link bandwidth is $10^{8}$ bits per second and that the propagation delay in the link is $5$ nanoseconds per meter. Every transmitted data byte is assigned a unique sequence number. Let $N$ be …

Suppose a $5$-bit message is transmitted from a source to a destination through a noisy channel. The probability that a bit of the message gets flipped during transmission is $0.01$. Flipping of each bit is independent of one another. The probability that the message is delivered error-free to the destination is ___________ (rounded off to three decimal …

​Node $\text{X}$ has a $\text{TCP}$ connection open to node $\text{Y}$. The packets from $\text{X}$ to $\text{Y}$ go through an intermediate $\text{IP}$ router $\mathrm{R}$. Ethernet switch $\mathrm{S}$ is the first switch on the network path between $\mathrm{X}$ and $\mathrm{R}$. Consider a packet sent from $\mathrm{X}$ to …

Consider an Ethernet segment with a transmission speed of $10^{8} \mathrm{bits} / \mathrm{sec}$ and a maximum segment length of $500$ meters. If the speed of propagation of the signal in the medium is $2 \times 10^{8} \mathrm{~meters} / \mathrm{sec}$, then the minimum frame size (in bits) required for collision detection is ___________.

Consider an enterprise network with two Ethernet segments, a web server and a firewall, connected via three routers as shown below. What is the number of subnets inside the enterprise network?

Assume that a $12$-bit Hamming codeword consisting of $8$-bit data and $4$ check bits is $d_8d_7d_6d_5c_8d_4d_ 4d_3d_2c_4d_1c_2c_1$, where the data bits and the check bits are given in the following tables: …

Consider the cyclic redundancy check $\text{(CRC)}$ 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 $\text{CRC}$ scheme. The transmitted bit string is denoted by …

Consider a network using the pure $\text{ALOHA}$ 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 retransmitted frames due to collisions) is modelled as a …

Consider that $15$ machines need to be connected in a LAN using $8$-port Ethernet switches. Assume that these switches do not have any separate uplink ports. The minimum number of switches needed is ______

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 …

A computer network uses polynomials over $GF(2)$ for error checking with $8$ bits as information bits and uses $x^{3}+x+1$ as the generator polynomial to generate the check bits. In this network, the message $01011011$ is transmitted as:

A sender $S$ sends a message $m$ to receiver $R$, which is digitally signed by $S$ with its private key. In this scenario, one or more of the following security violations can take place. $S$ can launch a birthday attack to replace $m$ with a fraudulent message $A$ third party attacker can launch a birthday attack to replace $m$ with a …

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

For the $\text{IEEE 802.11 MAC}$ protocol for wireless communication, which of the following statements is/are TRUE? At least three non-overlapping channels are available for transmissions. The RTS-CTS mechanism is used for collision detection. Unicast frames are ACKed.

A network has a data transmission bandwidth of $20 \times 10^{6}$ bits per second. It uses CSMA/CD in the MAC layer. The maximum signal propagation time from one node to another node is $40$ microseconds. The minimum size of a frame in the network is __________ bytes.

In an Ethernet local area network, which one of the following statements is TRUE?

Consider a LAN with four nodes $S_1, S_2, S_3,$ and $S_4$. Time is divided into fixed-size slots, and a node can begin its transmission only at the beginning of a slot. A collision is said to have occurred if more than one node transmits in the same slot. The probabilities of generation of a frame in a time slot by $S_1, S_2, S_3,$ and $S_4$ are …

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 $2 \times10^8m/s$ 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 …

In the diagram shown below, $L1$ is an Ethernet LAN and $L2$ is a Token-Ring LAN. An $IP$ packet originates from sender $S$ and traverses to $R$, as shown. The links within each $\text{ISP}$ and across the two $\text{ISP}$s, are all point-to-point optical links. The initial value of the $\text{TTL}$ field is $32$. The maximum possible value …