ProbeCast: MANET Admission Control via Probing

1. ProbeCast: MANET Admission Control via Probing Soon Y. Oh, Gustavo Marfia, and Mario Gerla Dept. of Computer Science, UCLA Los Angeles, CA 90095, USA {soonoh, gmarfia, gerla}@cs.ucla.edu

2. Introduction • Multicast “inelastic” streams • Inelastic flow - the rate cannot be elastically controlled (unlike TCP) • Real time flows: situation awareness dissemination; surveillance data/video, etc • Important in tactical/emergency MANETs • Traditional resource reservation ineffective in MANETs • Bookkeeping is very cumbersome in multicast (as number of destinations increases); • Also, mobility requires continuous re-adjustments • Without reservations: • Flow allocation can be “unfair”  possible capture • Network may get congested

3. Unfairness Example (unicast) • 3 parallel inelastic flows; 500Kbps each • Interference between Flow 1 and 2 and Flow 2 and 3

4. Goal & Contribution • Achieving reliable QoS support of inelastic flows (e.g., video and audio stream) • ProbeCast: • Enable Call Admission Control and fair allocation of inelastic flows in MANETs without requiring prior resource reservation

5. ProbeCast: key insights • Insight #1: Resource Probing • No a priori resource allocation • Rather “probe” for resources to see if available • Insight #2: Pruning via Back-pressure • Back-pressure (“prune”) toward the source when resource is unavailable • Re-route or reject the inelastic flow • Insight #3: Neighborhood Proportional Drop (NPROD) • Local rate balancing using proportional dropping • Enforces fair channel sharing  “fair back-pressure”

6. ProbeCast: Example Backpressure (Pruning) Proportional Drop

7. ProbeCast: Probing • Assumptions: • End-to-End FEC – e.g. erasure coding – always ON • Each flow has packet drop threshold (say, 20%), beyond which the flow must be back-pressured • Probing • Each node measures own packet drop rate • It broadcasts to one hop neighbors own drop rate via piggybacking on data packets

8. The node estimates packet drop probability DPF for each flow F • It broadcasts to one hop neighbors the DPF value 8

9. ProbeCast: N-PROD • Neighborhood Proportional Drop (N-PROD) • Distributed fairness scheme • First introduced and evaluated in FairCast (MSWIM 2008) • Overhearing neighbors’ drop probabilities • Enforcing proportional drop among flows competing in the same contention domain • Forced drop from the queue • After transient, nodes in the same contention domain converge to fair share of the channel

10. ProbeCast: Pruning • Pruning • Flow Drop based on Threshold • Threshold is traffic class and flow age dependent; • Drop Threshold stamped in packet header • Typically, incoming flow has lower threshold than incumbent • When drop rate is > threshold, a flow is backpressured • BckPr signal piggybacked on data packets whenever possible • Upstream node in turn will backpressure when all “children” have sent BckPr signal • Source action (upon receiving backpressure signal): • Re-route if there is alternate route; • Otherwise reject the flow

11. ProbeCast Example • Three flows in the same contention domain. Bar graphs shows packet delivery ratios • Flow 3 starts transmitting and other flows’ rate decreases (N-PROD). • Since Flow 3 drop rate exceeds the threshold, it is backpressured.

12. Simulation • Simulation setup • Qualnet simulations • Radio range 376m; 2Mbps capacity; 802.11b • 512B packets; 50KB queue in each node • Topologies • Three parallel flows • 30 nodes uniformly distributed in a 1000x1000m field • Experiments • N-PROD: to show proportional fairness • ProbeCast: to show proper rejection

13. S3 Source Flow 3 Forwarder F3 R3 Receiver Flow 2 S2 F2 R2 Flow 1 F1 R1 S1 Three Parallel Flow Topology • F1, F2, and F3 are within the same contention domain • No interference between sources and forwarders • No interference between forwarders and receivers • Staggered Transmission starts: 1s, 10s, 20s

14. Three Even Parallel Flows Uniform nominal rate = 500Kpbs Flows 2 has higher packet drop rate without N-PROD N-PROD restores fairness 14

15. Three Even Parallel Flows (cont) Uniform nominal rate = 500Kpbs Aggregated throughput of the three flows Fairness comes at the cost of degraded total throughput 15

16. Three Uneven Parallel Flows Flow1 = 800Kbps, Flow2 = 400Kbps, and Flow3=200Kbps Without N-PROD, Flow 1 and 3 capture the channel With N-PROD proportional drop yields 8:4:2 ratio 16

17. Two Flows in Random Topology Session 1 Session 2 • 30 nodes in 1000 by 1000 meter • Flow 1: 200Kbps video stream, 9 members • Flow 2: 40Kbps audio stream, 3 members Session 2

18. Two Flows in Random Topology • Session 1 captures channel in ODMRP so session 2 starves • N-PROD achieves fairness • All members in session 1 and 2 receive more than 50% packets • Drop Threshold = 50%

19. Three Flows in Random Topology • Three multicast sessions, each session has 1 source and 3 members • 30 nodes in 1000 by 1000 meter • Data transmission starts Session1 T=1s, Session2 T=10s, and Session3 T=20s • 500Kbps traffic; drop threshold = 50% Session 1 Session 2 Session 3

20. Three Flows in Random Topology (cont) • Three multicast sessions compete within the same collision domain • Session 2 is rejected (it came after Session 1 - initially lower threshold)

21. Conclusion • N-PROD achieves proportional bandwidth share in the same contention domain • ProbeCast uses probing and backpressure to accept feasible flows and reject unfeasible ones. • Probecast can also handle inelastic unicast (a special case of multicast)