Chuah ecs152aeec173a 2 2 30 points random access a 16

Chuah ECS152A/EEC173A
2
2. (30 points) Random Access .
(a) (16 pt.) Compare, briefly in 1 or 2 sentences, unslotted Aloha with CSMA/CD according to the
following:
• (4 pt.) The kinds of channel feedback required.
Unslotted Aloha: receiver will broadcast received signal. Sender waits for round-trip-
delay to find out whether transmission is successful.
CSMA/CD: Listen to carrier while transmitting a frame to detect collision.
• (4 pt.) The retransmission methods.
Unslotted Aloha: Wait a random amount of time and retransmit
CSMA/CD: Wait a random amount of time and sense the channel again, if idle, send,
otherwise, keep sensing the channel.
• (4 pt.) Which one (give reasons) works better if the propagation delay is large?
• (4 pt) Which one (give reasons) works better when the load is high?
(b) (4 pt.) Describe p-persistent CSMA without collision detection
(c) (5 pt.) State how changing the value of p from 1 to 0 affects throughput and delay of p-persistent
CSMA without collision detection.