requires one master node to poll each of the nodes in a round-robin fashion.

CSMA with collision detection

collision detection … in wired, … with wireless

colliding transmissions aborted, reducing channel wastage

"invites" other nodes to transmit in turn.

… play role in in determining collision probability

If NIC senses channel: if…: start frame transmission

CSMA/CD Has … performance than ALOHA

CSMA/CD

efficient at low load: single node can fully utilize channel

there is no master node.

Inefficient at low load: delay in channel access, 1/N bandwidth allocated even if only 1 active
node!

control token passed from one node to next sequentially.

Time Division, Frequency Division

carrier sensing: easy in some technologies (wire), hard in others

CSMA/CD used in Ethernet

switches have link-layer addresses associated with their interfaces

used for layer 3 (network layer) forwarding

(for most LANs) burned in NIC ROM, also sometimes software settable

MAC flat address: portability can move interface from one LAN to another.