Computer Networks — GATE Previous Year Questions

The message 11001001 is to be transmitted using the CRC polynomial \(x^{3}+1\) to protect it from errors. The message that should be transmitted is:

A computer on a 10 Mbps network is regulated by a token bucket. The token bucket is filled at a rate of 2 Mbps. It is initially filled to capacity with 16 Megabits. What is the maximum duration for which the computer can transmit at the full 10 Mbps?

Consider a source computer \(S\) transmitting a file of size \(10^{6}\) bits to a destination computer \(D\) over a network of two routers \(R_1\) and \(R_2\) and three links \(L_1, L_2, L_3\). \(L_1\) connects \(S\) to \(R_1\); \(L_2\) connects \(R_1\) to \(R_2\); and \(L_3\) connects \(R_2\) to \(D\). Let each link be of length 100 km. Assume signals travel over each link at a speed of \(10^{8}\) meters per second. Assume that the link bandwidth on each link is 1 Mbps. Let the file be broken down into 1000 packets each of size 1000 bits. Find the total sum of transmission and propagation delays in transmitting the file from \(S\) to \(D\).

Assume that source \(S\) and destination \(D\) are connected through two intermediate routers labelled \(R\), as shown below:

S --- R --- R --- D

Determine how many times each packet has to visit the network layer and the data link layer during a transmission from \(S\) to \(D\).

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 ________.

Consider a network connecting two systems located 8000 km apart. The bandwidth of the network is \(500 \times 10^{6}\) bits per second. The propagation speed of the media is \(4 \times 10^{6}\) meters per second. It is needed to design a Go-Back-N sliding window protocol for this network. The average packet size is \(10^{7}\) bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. Then, the minimum size in bits of the sequence number field has to be ________.

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 (1 Kbps = 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 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. The server-side TCP responds by sending an ACK, which is received by the client-side TCP. As per the TCP connection state diagram (RFC 793), in which state does the client-side TCP connection wait for the FIN from the server-side TCP?

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

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?

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 ________.