Data Center Networking with Multipath TCP Costin Raiciu University College London & Universitatea Politehnica Bucuresti Christopher Pluntke, UCL Adam Greenhalgh, UCL Sebastien Barre, Universite Catholique Louvain Damon Wischik. UCL Mark Handley, UCL UCL
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Data Center Networking with Multipath TCP Costin Raiciu University College London & Universitatea Politehnica Bucuresti Christopher Pluntke, UCL Adam Greenhalgh,
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Data Center Networking with Multipath TCP
Costin RaiciuUniversity College London & Universitatea Politehnica Bucuresti
Each hosts sends and receives from a single other randomly chosen host
Smallest amount of traffic that can fill the network
Multipath TCP in the Fat Tree Topology
Throughput Allocation
Performance depends on topology
VL2 BCube
Overloaded Fat Tree: better fairness with Multipath TCP
Centralized Scheduling
With RLB, it’s really hard to utilize FatTree.
Hedera [Fares et al.,2010] uses a centralized scheduler and flow switching. Start by using RLB Measure all flow throughput periodically. Any flow using more than 10% of its interface rate
is explicitly scheduled onto an unloaded link.
How does centralized scheduling compare with MPTCP?
MPTCP vs Centralized Dynamic Scheduling
Infinite
Centralized Scheduling MPTCP
Scheduling Interval
Can’t we just use many TCP connections?
Loss rate of MP-TCP (“linked”) vs multiple uncoupled TCP flows
Retransmit timeouts with MPTCP (“linked”) vs uncoupled TCP flows
MPTCP Linked Increases in DCs
Better fairness and less aggressive than uncoupled TCP
Improves throughput in dense traffic in BCube (25%)
The bigger picture
Topology
Routing
Resource Allocation
FatTree, VL2, Bcube, multi-rooted tree
MultipathTCP
Path Selection
OSPF, VLANs, etc.
?
Multipath TCP can utilize topologies TCP can’t
1Gb/s
1Gb/s
Requirement: a subset of hosts should be able to communicate at 10Gb/s
10Gb/s
Multipath TCP can utilize topologies TCP can’t [2]
Problem ToR switch failures wipe out tens of
hosts Repair time is on the order of days
Solution: use two ToRs/rack, multi-home servers
Single path TCP Single flows still get same max
throughput Which interface do I use?
With Multipath TCP Flows double their maximum
throughput Path selection automatic
Summary
Data center networking offers many paths between end-hosts. Yet: Random Load Balancing does a poor job of utilizing
them Centralized scheduling is laggy and has inherently
limited knowledge Multipath TCP naturally optimizes data center networks:
Improves throughput Improves fairness More robust than centralized scheduling
Question: what topologies does multipath TCP enable?