Congestion Control In wireless Networks [PAC: Perceptive Admission Control Protocol]

Goal Control the amount of traffic in the network Provide high quality service to all admitted traffic Ensure the network congestion point is not reached

Background: Impacted area

Background: Impacted area How is Reception Range defined the maximum separation between a sender and receiver for successful packet reception as RxR.

Background: Receiver interference distance (RID) CSR>RID>RxR

Background The distance between two senders to ensure proper packet reception at a receiver is RxR + RID. This distance holds for all possible network scenarios. At any distance smaller than RxR + RID, it is possible that the transmissions of two senders will interfere with a receivers ability to properly decode a packet.

Background The safe distance between two senders is 2RxR+RID

Determining the Available Bandwidth MAC Layer Congestion Window Queue Length Number of Collision These methods provide little or no information regarding network utilization if a node is not actively transmitting packets.

Determining the Available Bandwidth Channel Busy Time Transmitting Receiving Busy The total time within an interval that a node is transmitting packets,receiving packets or sensing packet transmissions.

Perceptive Admission Control New CSR A sender can consider only the traffic within this new CSR before admitting a new traffic

Contention-Aware Admission Control Protocol (CACP) A query message must be sent to all nodes within carrier sensing range. If all CSN detect enough available bandwidth then the flow is admitted.

Query flooding may fail S2 is an isolated node, but it does affected by the new traffic brought by S1 Solution: use high power packet transmission to send the query message

Contention-Aware Admission Control Protocol (CACP) V.S. PAC

Perceptive Admission Control To prevent the channel congestion, PAC ensures that the quantity of admitted traffic is below the network saturation point by reserving a small portion of the bandwidth. This prevents the channel from becoming congested and allows all admitted traffic to receive high delivery rates and low delay.

Mobility What would happen if two sender-receiver pairs move closer than the safe range ? 75% 75%

Mobility Each source monitors the available bandwidth Senders check available bandwidth after a random time and before sending a packet Random back-off time

Advantage PAC does not send query message, thus reduce the query overhead.

Conclusion PAC effectively limits the amount of data traffic to avoid congestion Provides consistent throughput, low packet loss and delay Useful in wireless application that requires high QoS such as multimedia applications

Questions..?