Chapter 6 Final

Question 1

Which of the following services may be implemented in a link-layer protocol?

Answer 1

-Flow control between directly connected nodes.
-Bit-level error detection and correction.
-Reliable data transfer between directly connected nodes.
-Coordinated access to a shared physical medium.
-Multiplexing down from / multiplexing up to a network-layer protocol.

Question 2

Which of the following statements is true about a two-dimensional parity check (2D-parity) computed over a payload?

Answer 2

• 2D-parity can detect any case of a single bit flip in the payload.
• 2D-parity can detect and correct any case of a single bit flip in the payload.
• 2D-parity can detect any case of two bit flips in the payload.

Question 3

Which of the following statements is true about both Pure Aloha, and CSMA (both with and without collision detection?

Answer 3

• There can be simultaneous transmissions resulting in collisions.
• Pure Aloha and CSMA can achieve 100% utilization, in the case that there is only one node that always has frames to send

Question 4

Polling and token-passing protocols. Which of the following statements is true about polling and token-passing protocols?

Answer 4

• These protocol can achieve close to 100% channel utilization, in the case that all nodes always have frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions)
• These protocol can achieve close 100% utilization, in the case that there is only one node that always has frames to send (the fact that the utilization is close to, but not exactly, 100% is due to a small amount of medium access overhead but not due to collisions)

Question 5

Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols are collision-free (e.g., collisions will never happen)?

Answer 5

TDMA, FDMA
Polling

Question 6

Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. Which of these protocols requires some form of centralized control to mediate channel access?

Answer 6

TDMA, FDMA
Polling

Question 7

Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is the maximum channel utilization 1 (or very close to 1)?

Answer 7

TDMA and FDMA
Polling

Question 8

Consider the following multiple access protocols that we’ve studied: (1) TDMA, and FDMA (2) CSMA (3) Aloha, and (4) polling. For which of these protocols is there a maximum amount of time that a node knows that it will have to wait until it can successfully gain access to the channel?

Answer 8

TDMA and FDMA
Polling

Question 9

Which of the following statements is true about channel partitioning protocols?

Answer 9

• There can be times when the channel is idle, when a node has a frame to send, but is prevented from doing so by the medium access protocol.
• Channel partitioning protocols can achieve 100% channel utilization, in the case that all nodes always have frames to send.