Computer Network GATE Question Answers with Explanation.
Q1 – Consider a network with three routers 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 Q−R fails. Assume that P and Q send out routing updates at random times, each at the same average rate. The probability of a routing loop formation (rounded off to one decimal place) between P and Q, leading to count-to-infinity problem, is___________. (GATE 2022)
Ans – (0.5)
Explanation –Â
Q2 – Consider a 100 Mbps link between an earth station (sender) and a satellite (receiver) at an altitude of 2100 km. The signal propagates at a speed of 3×108 m/s. The time taken (in milliseconds, rounded off to two decimal places) for the receiver to completely receive a packet of 1000 bytes transmitted by the sender is_________. (GATE 2022)
Ans – (7.07 to 7.09)
Explanation –
Q3 – Consider the data transfer using TCP over a 1 Gbps link. Assuming that the maximum segment lifetime (MSL) is set to 60 seconds, the minimum number of bits required for the sequence number field of the TCP header, to prevent the sequence number space from wrapping around during the MSL is____________. (GATE 2022)
Ans – (33)
Explanation –
Q4 – Consider two files systems A and B, that use contiguous allocation and linked allocation, respectively. A file of size 100 blocks is already stored in A and also in B. Now, consider inserting a new block in the middle of the file (between 50th and 51st block), whose data is already available in the memory. Assume that there are enough free blocks at the end of the file and that the file control blocks are already in memory. Let the number of disk accesses required to insert a block in the middle of the file in A and B are nA and nB respectively, then the value of nA + nB is_________. (GATE 2022)
Ans – (153)
Explanation –
Q5 – Consider a demand paging system with four-page frames (initially empty) and LRU page replacement policy. For the following page reference string
        7, 2, 7, 3, 2, 5, 3, 4, 6, 7, 7, 1, 5, 6,1
the page fault rate, defined as the ratio of number of page faults to the number of memory accesses (rounded off to one decimal place) is_________. (GATE 2022)
Ans – (0.6)
Explanation –