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PRESTO’08. Latency Equalization: A Programmable Routing Service Primitive. Minlan Yu [email protected] Joint work with Marina Thottan, Li Li at Bell Labs. Motivation. Latency EQualization (LEQ) service Online interactive applications require equalized delay among multiple users - PowerPoint PPT Presentation
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Latency Equalization:A Programmable Routing Service Primitive
Minlan [email protected]
Joint work with Marina Thottan, Li Li at Bell Labs
PRESTO’08
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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
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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
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LEQ Service Reducing latency difference
Difference of Maximum delay and minimum delay
client1
client2
server
client3
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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
serverclient1
client2 client3
hub
hub
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
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
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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
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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 applicationsControl Plane
LEQ routing for gaming
OSPFLEQ routingFor concert
LEQ routingFor trading
FIB FIBFIB FIB
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
client10
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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
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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
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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
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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
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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
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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
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Acknowledgement Grenville Armitage, Swinburne University of
Technology Wu-Chang Feng, Washington State
University Jennifer Rexford, Princeton University Thomas Woo, Bell Labs
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Thanks! Q&A?
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Static Analysis Telstra network
80%
5 hubs are sufficient
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Static Analysis AT&T network
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Premise of LEQ: Trading delay for delay difference