Computer Networks — Test 14

Correct Answer: A. A. T propagation
Explanation: In carrier sense multiple access, the stations sense the medium whether it is idle or not. This information is sent by the station which is using the medium, using propagation of a signal. The propagation delay in the signal causes the collision.

Correct Answer: A. A. True
Explanation: In slotted aloha, the time is divided into time slots, that are of T(frame) length. The stations are instructed to send the frames at the starting of the time slot. Still there is a chance for collision, if 2 frames are started at the same it. This is why vulnerable time is equal to the time taken by a frame to be sent to the destination.

Correct Answer: D. D. Bandwidth division multiple access
Explanation: The channelization protocols use frequency, time and code to divide the bandwidth of the channel. Bandwidth is divided into frequency bands in FDMA, same bandwidth is used by the stations in TDMA.

Correct Answer: A. A. Preamble bits
Explanation: Time division multiple access allocates the time slots for station to use the channel. These time slots are synchronized by preamble bits, which acts as guard time between two time slots.

Correct Answer: B. B. Public key cryptography
Explanation: Cryptography is mainly categorized into two types; symmetric key cryptography and asymmetric key cryptography(public key cryptography). Symmetric key cryptography uses only one key for both encryption and decryption.

Correct Answer: D. D. Juhhw khu
Explanation: Caesar cipher is the substitution cipher, which belongs to classical cryptography. Cipher text will be obtained by replacing the plain text letters with letters three places further from them. If further letter is ‘z’, then process will circularly follows ‘a’.

Correct Answer: A. A. Tkmtteataeeohpry
Explanation: Rail fence is the transposition technique, that belongs to classical cryptography. First the plain text is written in a sequence of diagonals with defined number of rows, then the cipher text is read off as a sequence of all the rows from starting to end.

Correct Answer: B. B. Classical and modern
Explanation: Symmetric key cryptography has two types; classical and modern. Classical cryptography again divided into two types; transposition and substitution. Modern cryptography is of two types; stream cipher and block cipher.

Correct Answer: D. D. Diffie-hellman
Explanation: Diffie-Hellman is the first asymmetric cipher and well known for its logarithm computations. It is used at its best to transmit the secret key between users for further symmetric encryption of messages.

Correct Answer: D. D. Quick encryption and decryption
Explanation: Quick encryption and decryption is done in symmetric key cryptography. Because, it uses less resources and cipher text length will be small or same as plain text. It encrypts huge amount of data quickly and provides confidentiality.