GATE CS Computer Networks questions

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 ______

In an RSA cryptosystem, the value of the public modulus parameter $n$ is $3007$. If it is also known as that $\phi(n)=2880$ where $\phi()$ denotes Euler’s Totient Function, then the prime factor of $n$ which is greater than $50$ 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 …

Consider an IP packet with a length of $4,500\;\text{bytes}$ that includes a $20\text{-byte}\;\textsf{IPv4}$ header and a $40\text{-byte}$ TCP header. The packet is forwarded to an $\textsf{IPv4}$ router that supports a Maximum Transmission Unit (MTU) of $600\;\text{bytes}$. Assume that the length of the IP header in all the outgoing fragments of …

Consider a long-lived $\text{TCP}$ session with an end-to-end bandwidth of $1\; \text{Gbps}\; (=10^9$ bits-per-second$).$ The session starts with a sequence number of $1234$. The minimum time (in seconds, rounded to the closet integer) before this sequence number can be used again is _________.

Consider the following statements regarding the slow start phase of the TCP congestion control algorithm. Note that cwnd stands for the TCP congestion window and MSS window denotes the Maximum Segments Size: The cwnd increases by $2$ MSS on every successful acknowledgment The cwnd approximately doubles on every successful acknowledgment The cwnd increases …

Match the following: $$\begin{array}{|l|l|}\hline \textbf{Field} & \textbf{Length in bits} \\ \hline \text{P. UDP Header's Port Number} & \text{I. 48} \\ \text{Q. Ethernet MAC Address} & \text{II. 8} \\ \text{R. IPv6 Next Header} & \text{III. 32} \\ \text{S. TCP Header's Sequence Number} & \text{IV. 16} \\ \hline \end{array}$$

The values of parameters for the Stop-and-Wait ARQ protocol are as given below: Bit rate of the transmission channel $= 1$ Mbps. Propagation delay from sender to receiver $= 0.75$ ms. Time to process a frame $= 0.25$ ms. Number of bytes in the information frame $= 1980$. Number of bytes in the acknowledge frame $= 20$. Number of overhead bytes in …

In a RSA cryptosystem, a participant $A$ uses two prime numbers $p = 13$ and $q = 17$ to generate her public and private keys. If the public key of $A$ is $35$, then the private key of $A$ is __________ .

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 a TCP client and a TCP server running on two different machines. After completing data transfer, the TCP client calls close to terminate the connection and a FIN segment is sent to the TCP server. Server-side TCP responds by sending an ACK, which is received by the client-side TCP. As per the TCP connection state diagram $\text{(RFC 793)}$, in …

Consider two hosts $X$ and $Y$, connected by a single direct link of rate $10^6\; \text{bits/sec}$. The distance between the two hosts is $10,000\;\text{km}$ and the propagation speed along the link is $2 \times 10^8 \;\text{m/sec}$. Host $X$ sends a file of $50,000\;\text{bytes}$ as one large message to host $Y$ continuously. Let the …

The maximum number of $\textsf{IPv4}$ router addresses that can be listed in the record route (RR) option field of an $\textsf{IPv4}$ header is______.

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

Consider the following statements about the routing protocols. Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) in an $\textsf{IPv4}$ network. RIP uses distance vector routing RIP packets are sent using UDP OSPF packets are sent using TCP OSPF operation is based on link-state routing Which of the above statements are CORRECT?

Consider socket API on a Linux machine that supports connected UDP sockets. A connected UDP socket is a UDP socket on which connect function has already been called. Which of the following statements is/are CORRECT? A connected UDP socket can be used to communicate with multiple peers simultaneously. A process can successfully call connect function again for …

For a host machine that uses the token bucket algorithm for congestion control, the token bucket has a capacity of $1$ $\text{megabyte}$ and the maximum output rate is $20$ $\text{megabytes}$ per $\text{second}$. Tokens arrive at a rate to sustain output at a rate of $10$ $\text{megabytes}$ per $\text{second}$. The token bucket is currently …

An IP datagram of size $1000$ $\text{bytes }$arrives at a router. The router has to forward this packet on a link whose MTU (maximum transmission unit) is $100$ $\text{bytes }$. Assume that the size of the IP header is $20$ $\text{bytes }.$ The number of fragments that the IP datagram will be divided into for transmission is________.

A sender uses the Stop-and-Wait $\text{ARQ}$ protocol for reliable transmission of frames. Frames are of size $1000$ bytes and the transmission rate at the sender is $80\;\textsf{Kbps} (1\textsf{Kbps} = 1000\;\text{ bits/second}).$ Size of an acknowledgment is $100$ bytes and the transmission rate at the receiver is $8\;\textsf{Kbps.}$ The one-way …