Multiple Access shared transmission medium a receiver can hear multiple transmitters a transmitter can be heard by multiple receivers the major problem with multi-access is allocating the channel between the users the nodes do not know when the other nodes have data to send Need to coordinate transmissions
Carrier Sense Multiple Access(CSMA) In certain situations nodes can hear each other by listening to the channel “Carrier Sensing CSMA: Polite version of Aloha Nodes listen to the channel before they start transmission Channel idle=> Transmit Channel busy = Wait (join backlog) When do backlogged nodes transmit? When channel becomes idle backlogged nodes attempt transmission with probability q=1 Persistent protocol, q=1 Non-persistent protocol,< 1
Optimal Routing View routing as\global\ optimization problem Assumptions: The cost of using a link is a function of the flow on that link The total network cost is the sum of the link costs The required traffic rate between each source-destination pair is known in advance Traffic between source-destination pair can be split along multiple paths with infinite precision