GATE CS Computer Networks questions

Consider routing table of an organization’s router shown below: …

Consider a network with three routers $\text{P, Q, R}$ shown in the figure below. All the links have cost of unity. The routers exchange distance vector routing information and have converged on the routing tables, after which the link $\text{Q-R}$ fails. Assume that $\text{P}$ and $\text{Q}$ send out routing updates at random times, each at the same …

Consider a $100 \; \text{Mbps}$ link between an earth station (sender) and a satellite (receiver) at an altitude of $2100 \; \text{km}.$ The signal propagates at a speed of $3 \times 10^{8} \; \text{m/s.}$ The time taken $\text{(in milliseconds,} \; \textit{rounded off to two decimal places})$ for the receiver to completely receive a packet of …

Consider the data transfer using $\text{TCP}$ over a $1 \; \text{Gbps}$ link. Assuming that the maximum segment lifetime $\text{(MSL)}$ is set to $60 \; \text{seconds},$ the minimum number of bits required for the sequence number field of the $\text{TCP}$ header, to prevent the sequence number space from wrapping around during the $\text{MSL}$ is …

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

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: …

A $\text{TCP}$ server application is programmed to listen on port number $P$ on host $S$. A $\text{TCP}$ client is connected to the $\text{TCP}$ server over the network. Consider that while the $\text{TCP}$ connection was active, the server machine $S$ crashed and rebooted. Assume that the client does not use the $\text{TCP}$ keepalive timer. …

Consider two hosts $P$ and $Q$ connected through a router $R$. The maximum transfer unit $\text{(MTU)}$ value of the link between $P$ and $R$ is $1500$ bytes, and between $R$ and $Q$ is $820$ bytes. A $\text{TCP}$ segment of size $1400$ bytes was transferred from $P$ to $Q$ through $R$, with $\text{IP}$ identification value as …

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 …

Consider the three-way handshake mechanism followed during $\text{TCP}$ connection establishment between hosts $P$ and $Q$. Let $X$ and $Y$ be two random $32$-bit starting sequence numbers chosen by $P$ and $Q$ respectively. Suppose $P$ sends a $\text{TCP}$ connection request message to $Q$ with a $\text{TCP}$ segment having …

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 computer network using the distance vector routing algorithm in its network layer. The partial topology of the network is shown below. The objective is to find the shortest-cost path from the router $R$ to routers $P$ and $Q$. Assume that $R$ does not initially know the shortest routes to $P$ and $Q$. Assume that $R$ has three …

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 the following statements about the functionality of an $\textsf{IP}$ based router. A router does not modify the $\textsf{IP}$ packets during forwarding. It is not necessary for a router to implement any routing protocol. A router should reassemble $\textsf{IP}$ fragments if the $\textsf{MTU}$ of the outgoing link is larger than the size of …

Assume that you have made a request for a web page through your web browser to a web server. Initially the browser cache is empty. Further, the browser is configured to send $\textsf{HTTP}$ requests in non-persistent mode. The web page contains text and five very small images.The minimum number of $\textsf{TCP}$ connections required to display the web …

An organization requires a range of IP address to assign one to each of its $1500$ computers. The organization has approached an Internet Service Provider (ISP) for this task. The ISP uses CIDR and serves the requests from the available IP address space $202.61.0.0/17$. The ISP wants to assign an address space to the organization which will minimize the …

Consider a $\textsf{TCP}$ connection between a client and a server with the following specifications; the round trip time is $6$ ms, the size of the receiver advertised window is $50$ KB, slow-start threshold at the client is $32$ KB, and the maximum segment size is $2$ KB. The connection is established at time $t=0$. Assume that there are no …

Which of the following protocol pairs can be used to send and retrieve e-mails (in that order)?

Consider three machines M, N, and P with IP addresses $100.10.5.2, \: 100.10.5.5$, and $100.10.5.6$ respectively. The subnet mask is set to $255.255.255.252$ for all the three machines. Which one of the following is true?

Suppose that in an IP-over-Ethernet network, a machine X wishes to find the MAC address of another machine Y in its subnet. Which one of the following techniques can be used for this?