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Latency Equalization: A Programmable Routing Service Primitive

PRESTO’08 Latency Equalization: A Programmable Routing Service Primitive Minlan Yu minlanyu@cs.princeton.edu Joint work with Marina Thottan, Li Li at Bell Labs Motivation Latency EQualization (LEQ) service Online interactive applications require equalized delay among multiple users

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Latency Equalization: A Programmable Routing Service Primitive

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  1. PRESTO’08 Latency Equalization:A Programmable Routing Service Primitive Minlan Yu minlanyu@cs.princeton.edu Joint work with Marina Thottan, Li Li at Bell Labs

  2. Motivation • Latency EQualization (LEQ) service • Online interactive applications require equalized delay among multiple users • Online gaming • Players vote to exclude players with higher lag • Distributed online music concert • Delay difference among musicians at different places degrade music quality • Online trading • Unfair advantage to shopping agents with lower delay

  3. Latency Compensation Techniques • Server side solutions • Buffer packets till all clients response arrive • Expensive due to processing overhead • Limits on number of clients • Client side solutions • Buffer the packets to wait for other clients • Requires coordination among clients • Easy to cheat • We need network service for LEQ

  4. Reducing latency difference Difference of Maximum delay and minimum delay server client1 client2 client3 LEQ Service

  5. LEQ Architecture - Basic Idea • Avoid changing every router • Place a few hub routers in the network • Add customized logic to hub routers • Redirect traffic through hub routers hub server client1 hub client2 client3

  6. Easy to Deploy • Require only a few programmable routers • Allow incremental deployment • With one hub in the network, we can reduce delay difference by 40% on average compared with OSPF • No modification of underlying routing protocols • Can be implemented as an overlay

  7. LEQ Architecture • Architecture • Select a set of hubs for each client • Set up tunnels between clients and hubs, hubs and servers. • MPLS tunnels or packet encapsulation • Hub routers redirect packets to servers

  8. Hub Router Implementation • Packet classifier • Identify application from src, dst, port • Identify class of packets within an application • Initial game setup packets: shortest path routing • Interactive event packets: LEQ routing FIB Packet classifier

  9. Hub Router Implementation • Customize routing for each application • Different applications may have different max delay bound; different client, server location • LEQ routing for gaming, live concert, trading • OSPF routing for other applications Control Plane LEQ routing For trading LEQ routing for gaming OSPF LEQ routing For concert FIB FIB FIB FIB

  10. Other benefits of hubs • Add service-specific logic to a few enhanced routers in the network • Application level packet processing • Gaming: Update aggregation, packet inspection • Concert: Echo cancellation • Multicast • Server multicast to hubs • Hubs then multicast to their clients • Load balancing among servers • Hubs can select the least-loaded server for the client 10

  11. Hub Placement Problem • Input • Location of client/server edge routers • Maximum number of hub routers (M) • Number of hub routers per client (m) • Output: • A set of m hubs for each client • Goal: • Minimize delay difference among clients

  12. Problem Complexity • We proved it is NP-hard and inapproximable • Reduced to set cover problem • Greedy hub placement algorithm • Based on multi-set cover algorithm • See details in the paper

  13. Evaluation • Static analysis • Use Rocketfuel Data with different ISPs • Focus on lightly loaded network • propagation delay • Result • LEQ achieve 80% reduction of latency difference compared with shortest path routing • Reduce from 35ms to 5ms • Only need to place 5 hubs in the network • Similar maximum delay of LEQ and OSPF

  14. Evaluation (cont.) • Dynamic Analysis • Under dynamic traffic condition • Focus on congested network • Consider both propagation delay and queuing delay • Result • LEQ routing can get around congestion

  15. Alternative Network-based Solutions OSPF No delay difference consideration Tune weights for each application Computationally hard Source routing Clients need to know the global network condition Require collaboration among clients Hard to compute and implement 15

  16. Conclusion • Interactive online applications • New requirement on delay difference • Latency Equalization service • Place a few hubs to provide latency-equalized, reliable paths • Deployment on programmable routers • Easy to implement and deploy

  17. Acknowledgement • Grenville Armitage, Swinburne University of Technology • Wu-Chang Feng, Washington State University • Jennifer Rexford, Princeton University • Thomas Woo, Bell Labs

  18. Thanks! • Q&A?

  19. Static Analysis Telstra network 5 hubs are sufficient 80% 19

  20. Static Analysis • AT&T network

  21. Premise of LEQ: Trading delay for delay difference 21

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