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

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: Receiverinterference 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..?