MAC(Media Access Control)

Random Access(Contention)

• No station is superior to another station and none is assigned control over another

ALOHA

• Potential collision
• allow multiple access
• After accept request packet, receiver immediately sends ACK
• All stations try to resend their frames after time out period
• If collision occur, Ignore the packet

Slotted ALOHA

• divided the time into slots of T second and force the station to send only at the beginning of the time slot

 

CSMA (Carrier Detection Multiple Access)

• Before each node approaches a shared medium to transmit a frame, First of all, check if the media is in use and then multi-access.
• Just before the packet was sent out, - check whether the channel is busy or not by detecting the carrier

Listen Before Talk (LBT)

• If the channel is empty, send out the packets.
• If in use, wait until the channel is empty

 

What patterns of behavior will the media take in CSMA immediately after free?

 

1-Persistent CSMA

• After the station find the line idle, It sends its frame immediately (with probability 1)

nonpersistent CSMA

• If the line is Idle, it sends immediately
• If the line is not idle, it waits a random amount of the time and the sense the line again

p-persistent CSMA

• With probability p, the station sends its frame
• With probability q(1-p), the station waits for the beginning of the next time slot and check the line again

 

CSMA/CD

• No ACK
• Listen while Talk (LWT)
• if collision wait a second (Backoff)

CSMA/CA

• After finding the idle, wait a few second(IFS; Interframe Space), and sends

 

CSMA/CD

 

 

 

Controlled-Access 

• consult one another to find which station has the right to send

 

Reservation

• a station needs to make a reservation before sending data.

Polling

• It is up to the primary device to determine which device is allowed to use the channel at a given time

 

Token passing

• Systems with tokens have the authority to send data

 

Channelizaion

• FDMA (Frequency-Division Multiple Access)
• TDMA (Time-Division Multiple Access)
• CDMA (Code-Division Multiple Access)