1 Congestion Control Outline Queuing Discipline Reacting to Congestion Avoiding Congestion.
Congestion Control In wireless Networks [ PAC: Perceptive Admission Control Protocol]
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Transcript of Congestion Control In wireless Networks [ PAC: Perceptive Admission Control Protocol]
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Congestion Control In Congestion Control In wireless Networkswireless Networks
[[PAC: Perceptive Admission Control Protocol]PAC: Perceptive Admission Control Protocol]
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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
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Background: Impacted areaBackground: Impacted area
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• How is Reception Range defined
the maximum separation between a sender and receiver for successful packet reception as RxR.
Background: Impacted areaBackground: Impacted area
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Background: Receiver interference Background: Receiver interference distance (RID)distance (RID)
• CSR>RID>RxR
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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.
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BackgroundBackground
• The safe distance between two senders is 2RxR+RID
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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.
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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.
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Perceptive Admission ControlPerceptive Admission Control
New CSR
A sender can consider only the traffic within this new CSR before admitting a new traffic
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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.
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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
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Contention-Aware Admission Control Contention-Aware Admission Control Protocol (CACP) V.S. PACProtocol (CACP) V.S. PAC
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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.
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MobilityMobility
• What would happen if two sender-receiver pairs move closer than the safe range
75% 75% ?
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MobilityMobility
• Each source monitors the available bandwidth
• Senders check available bandwidth after a random time and before sending a packet
• Random back-off time
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AdvantageAdvantage
• PAC does not send query message, thus reduce the query overhead.
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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
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Questions..?