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Auction or Tâtonnement – Finding Congestion Prices for Adaptive Applications

Xin Wang Henning SchulzrinneColumbia University

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Outline

Motivations Goal and scope Pricing strategies Congestion pricing Performance studies Conclusion

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Motivations

Two types of congestion pricing models in Internet today Tâtonnement

Iteratively update price that aggregate user demand approaches available bandwidth

Auction Allocate bandwidth based on users’ bidding price

No work comparing their performance, and little work address the practical issues

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Goal and Scope

Compare tâtonnement and auction Develop comparable pricing models Compare the performances Address issues for practical usages

Scope Network:

periodical price adjustments/resource allocations Users:

short-term reservation/demand adaptations

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Pricing Strategies

Holding price and charge: based on cost of blocking other users by

holding bandwidth even without sending data Usage price and charge:

maximize the provider’s profit, constrained by resource availability

Congestion price and charge: drive demand to supply level (tâtonnement or

auction)

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Congestion Pricing

Tâtonnement process Congestion charge proportional to excess demand

relative to target utilization M-bid auction model

User indicates its willingness to pay a premium for different bandwidths under congestion through bids

Congestion price: charge highest rejected bid price Features:

reduce uncertainty: user can express multiple preferences reduce signaling bursts: user provides bids in advance reduce setup delay: inter-auction admission allowed support periodical auctions

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Resource Allocations

Tâtonnement: User agent: determines the optimal demand based on

user preferences, network price, constrained by user budget and application QoS requirements.

Auction: Network: selects bids exceeding the auction price;

multiple bids of a user can be higher than the auction price, select the one with higher bandwidth (lower price per unit bandwidth).

User agents: adapt rate based on allocated bandwidth/QoS from network auctions.

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Simulation Topologies

Bottlenecks Studied

Topology 1

Topology 2

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Tâtonnement vs. auction

Tâtonnement can maintain the target utilization (0.9); With similar user benefit, auction has higher utilizationBlocking of tâtonnement is 40 times smaller than that of fixed pricing; blocking of auction is almost zero, with fractions of users delayed until next auction.

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Tâtonnement and auction have comparable total and average user benefitTâtonnement has higher congestion price, and hence allows for higher network revenue.

Tâtonnement vs. auction (cont’d)

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Impact of target utilization and M

Higher throughput of tâtonnement is at the cost of performances: higher blocking probability and lower user benefitAuction performance is robust to the variations of M

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Performance of topology-2

Similar trends as those of single bottleneck

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Conclusions

Performance comparisons Tâtonnement and auction

effectively control congestions have comparable performances function effectively over a range of parameters:

control periods, demand elasticity, different numbers of user multiplexing, different network topologies.

Auction has higher bandwidth utilization at a given user benefit, but has

higher implementation complexity longer setup delay

Tâtonnement has higher network revenue Resolve some practical issues for both schemes