Media Access Control Flashcards
What are some random access protocols?
Aloha
what does Aloha use?
radio waves
How many radio frequencies are used by Aloha?
2
One for transmission — packets from mainframe to clients
* One for receiving — packets from clients back to mainframe
How does aloha deal with collissions?
After a collision it waits a random amount of time before transmitting again
How did slotted aloha compare to aloha?
machines transmit packets at slotted times
they can send in any slot but start transmission at beginning of slot
Why is aloha reliable?
because client knows if packet has been received correctly through ACK packet
What does Ethernet use to deal with collisions?
CSMA/CD (carrier sense multiple access with collission detection)
How does CSMA work?
uses 2 algorithms
carrier sense
collision detection
What is carrier sense?
ethernet listens to bus to see if anything is being transmitted
if yes its wait till line is clear
then starts transmitting
What is collision detection?
if collision signals on the bus are different from the ones we are trying to send
jamming signal sent out
Whats exponential back-off?
delays packet resent
NI has a max delay before resending d
packet resent after random delay less than d
if collide again double d and pick randpm delay less tham max
repeat
is ethernet reliable?
NO it knows when packet is sent but not if its received or not
wifi is what based?
radio based so uses different kind of method
How is wifi different from aloha?
has a receiver so can sense transmissions
