June 2015 - Paper 3

26:

Which are the two modes of IP security?

A.	Transport and certificate
B.	Transport and tunnel
C.	Certificate and tunnel
D.	Preshared and transport
	Answer Report Discuss
	Option: B Explanation : IPsec can be implemented in a host-to-host transport mode, as well as in a network tunneling mode. In transport mode, only the payload of the IP packet is usually encrypted and/or authenticated. The routing is intact, since the IP header is neither modified nor encrypted. In tunnel mode, the entire IP packet is encrypted and/or authenticated. It is then encapsulated into a new IP packet with a new IP header. Tunnel mode is used to create virtual private networks for network-to-network communications, host-to-network communications and host-to-host communications. Click on Discuss to view users comments. Write your comments here: Updating your Comments.. Updating your Comments..

27:

A message "COMPUTERNETWORK" encrypted (ignore quotes) using columnar transposition cipher with a key "LAYER". The encrypted message is :

A.	CTTOEWMROPNRUEK
B.	MROUEKCTTPNROEW
C.	OEWPNRCTTUEKMRO
D.	UEKPNRMROOEWCTT
	Answer Report Discuss
	Option: C Explanation : Perform Transposition Cipher. Click on Discuss to view users comments. Write your comments here: Updating your Comments.. Updating your Comments..

28:

Suppose a digitized voice channel is made by digitizing 8 kHz bandwidth analog voice signal. It is required to sample the signal at twice the highest frequency (two samples per hertz). What is the bit rate required, if it is assumed that each sample requires 8 bits?

A.	32 kbps
B.	64 kbps
C.	128 kbps
D.	256 kbps
	Answer Report Discuss
	Option: C Explanation : The bit rate can be calculated as : 2 x 8000 x 8 = 128000 = 128 kbps. Click on Discuss to view users comments. Write your comments here: Updating your Comments.. Updating your Comments..

29:

The maximum payload of a TCP segment is :

A.	65,535
B.	65,515
C.	65,495
D.	65,475
	Answer Report Discuss
	Option: C Explanation : Each segment, including the TCP header, must fit in the 65515 byte IP payload, and the TCP header is 20 bytes at least, so the maximum payload of a TCP segment is 65515-20=65495 bytes. Click on Discuss to view users comments. Write your comments here: Updating your Comments.. Updating your Comments..

30:

An all-pairs shortest-paths problem is efficiently solved using :

A.	Dijkstra' algorithm
B.	Bellman-Ford algorithm
C.	Kruskal algorithm
D.	Floyd-Warshall algorithm
	Answer Report Discuss
	Option: D Explanation : The Dijsktra algrithm solves the Single-Source Shortest Paths (SSSP) problem. The Bellman�Ford algorithm is an algorithm that computes shortest paths from a single source vertex to all of the other vertices in a weighted digraph. It is slower than Dijkstra's algorithm for the same problem, but more versatile, as it is capable of handling graphs in which some of the edge weights are negative numbers. Kruskal algorithm is a minimum-spanning-tree algorithm where the algorithm finds an edge of the least possible weight that connects any two trees in the forest.It is a greedy algorithm in graph theory as it finds a minimum spanning tree for a connected weighted graph adding increasing cost arcs at each step. The Floyd Warshal algorithm takes the dynamic programming approach. This essentially means that independent sub-problems are solved and the results are stored for later use. The algorithm allows negative edges, but no negative cycles, as per usual with such shortest path problems. Click on Discuss to view users comments. Write your comments here: Updating your Comments.. Updating your Comments..

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June 2015 - Paper 3

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