The Network Layer Flashcards
What are the 2 multiple access protocols?
CSMA/CA
CSMA/CD
What does CSMA mean?
Carrier Sense Multiple Access / Collision Avoidance
Carrier Sense Multiple Access / Collision Detection
What does MA mean in CSMA/CD?
Multiple access - All computers attached to a single cable.
What does CS mean in CSMA/CD?
Carrier Sense - Any computer may transmit if the cable is unused.
How does CSMA/CD work?
A computer may detect that what it is transmitting is not what it is receiving, waits for a random interval and sends it again.
Why is randomization important?
It avoids repeated collisions.
Why is an exponentially doubling range important?
Machines will become more and more reluctant to send data, so you get more degradation the machines there are.
What does a switch do?
A switch builds a mapping from MAC addresses to ports, and uses it to forward packets.
What does MA mean in CSMA/CA?
Multiple Access - all computers use a shared radio frequency
What does CS mean in CSMA/CA?
Carrier Sense - any computer may transmit if the frequency is clear
How does Collision Avoidance work?
A computer finding the frequency clear transmits after an instant.
A computer finding the frequency busy counts down from a random value while the channel is clear, otherwise the count is frozen.
A computer then transmits and receives an acknowledgement.
What is the Hidden Station Problem
A computer may be in range of the base station, but out of the range of another computer.
Why is the hidden station problem a problem?
There may be a collision the two computers cannot detect each other.
How do you solve the hidden station problem?
The hidden station problem may be solved by reservation using ready to send (RTS) or clear to send (CTS) requests.
What is a Spread Spectrum Transmission and why is it used?
Wireless networks use spread spectrum transmission
(multiple frequencies) increasing immunity to noise.
