Congestion Control In Congestion Control In wireless Networkswireless Networks

[[PAC: Perceptive Admission Control Protocol]PAC: Perceptive Admission Control Protocol]

GoalGoal• 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 areaBackground: Impacted area

• How is Reception Range defined

the maximum separation between a sender and receiver for successful packet reception as RxR.

Background: Impacted areaBackground: Impacted area

Background: Receiver interference Background: Receiver interference distance (RID)distance (RID)

• CSR>RID>RxR

BackgroundBackground

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.

BackgroundBackground

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

Determining the Available Determining the Available BandwidthBandwidth

• 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 BandwidthDetermining the Available Bandwidth

Channel Busy TimeTransmittingReceivingBusy

The total time within an interval that a node is transmitting packets,receiving packets or sensing packet transmissions.

Perceptive Admission ControlPerceptive Admission Control

New CSR

A sender can consider only the traffic within this new CSR before admitting a new traffic

Contention-Aware Admission Control Contention-Aware Admission Control Protocol (CACP)Protocol (CACP)

A query message must be sent to all nodes within carrier sensing range.

If all CSN detect enough available bandwidththen the flow is admitted.

Query flooding may failQuery 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 Contention-Aware Admission Control Protocol (CACP) V.S. PACProtocol (CACP) V.S. PAC

Perceptive Admission ControlPerceptive 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.

MobilityMobility

• What would happen if two sender-receiver pairs move closer than the safe range

75% 75% ?

MobilityMobility

• Each source monitors the available bandwidth

• Senders check available bandwidth after a random time and before sending a packet

• Random back-off time

AdvantageAdvantage

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

ConclusionConclusion

• 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..?