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

2. 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

3. Background: Impacted area

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

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

6. 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.

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

8. 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.

9. 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.

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

11. 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.

12. 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

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

14. 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.

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

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

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

18. 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

19. Questions..?