The Delta Routing Project Lowloss Routing for Hybrid Private Networks

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The Delta Routing ProjectLow-loss Routing for
Hybrid Private Networks

• George Porter (UCB)
• Minwen Ji, Ph.D. (SRC - HP Labs)

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Outline

• Motivation/overview of corporate networks
• Problem Statement
• Architecture
• Two layers Physical and Overlay
• The Delta Protocol
• The DeltaTM Protocol
• Evaluation
• Conclusions

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Corporate Network ConstructionNetwork Layer

• Distributed Locations connected by leased lines
  due to
• Need for predictable performance
• Security
• Management and control
• Fixed initial cost, incremental additional cost
  due to traffic volume
• Not necessarily overprovisioned
• Reprovisioning on the timescale of days (or
  weeks)
• Expensive (compared to ISP connectivity

LON
SEA
OSPF
NYC
SF
DC
ALX
LA
DFW
HOU
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Corporate Network ConstructionOverlay Layer
ISP Connectivity

• ISP Connectivity alreay at selected nodes to
  provide
• Web/Email access
• VPN access to at-home or distance workers
• Business services
• Per-byte, ISP much cheaper than Intranet
• But no QoS
• Intranet corporate network with ISP links is
  called a Hybrid Private Network

LON
SEA
NYC
SF
DC
ALX
LA
DFW
HOU
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Problem of Congestion

• Flash traffic (video, backup, data transfer) or
  steady corporate growth can lead to periodic
  congestion
• Problem Statement
• Reduce congestion and packet loss on the Intranet
  by utilizing ISP connectivity while providing
  good end-to-end performance

LON
SEA
NYC
SF
DC
ALX
LA
DFW
HOU
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Architecture
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Architecture

• Overlay Layer
• Need to forward traffic around congested
  portions of the Intranet
• Measurement-based path construction
• Intermediate point may be better than last hop
  selection
• Metric include measured latency and local
  queuing delay
• Paths are selected on order of seconds or
  minutes
• Physical (Intranet) Layer
• Single-domain routing protocol (OSPF)
• Dijkstra
• Forwarding decision which packets go to
  Intranet and which go to the preselected overlay
  paths? (per packet)

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Physical Forwarding Algorithm

• Ji, Minwen. Dial-controlled Hash Reducing Path
  Oscillation in Multipath Networks. Proceedings
  of the International Conference on Computer
  Communications and Networks (ICCCN). Oct 2003.
• Current Algorithm
• Prefer physical path, but if physical queue full
  send to overlay layer.

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Overlay Path Selection Algorithms

• Static
• Lasthop
• Nexthop
• Random
• Dynamic
• Delta
• Minimize end-to-end delay
• DeltaTM
• Predict and avoid congestion by inferring global
  traffic matrix

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Delta Path Selection

• Find path to minimize the sum of
• Local Queue delay WAN delay Intranet delay

• Key feature is the use of locally obtained
  information

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Limitation of Delta Algorithm

• Since Delta uses local information, it might send
  traffic to an overloaded link

congested

• Can we avoid this?

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DeltaTM (Traffic Matrix)

• Key idea
• Dont choose paths that will subject the traffic
  to congestion
• Use the original Delta algorithm (minimize
  end-to-end delay) but throw out paths that will
  subject packets to congestion
• But how do we find out about remote congestion?
• Given that message flooding will likely be
  inaccurate and might make the problem worse

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Traffic Matrix Estimation


Topology Information

• Each node measures flows that transit through it
• Long-term averages are flooded to fill in the
  entries of the table that a node cant directly
  measure

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Evaluation

• Simple Example
• Algorithm-antagonistic Topologies
• Large-scale Topology (PlanetLab-based)

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Linear Topology
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Congestion Event
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Congestion Event
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Evaluation

• Simple Example
• Algorithm-antagonistic Topologies
• Large-scale Topology (PlanetLab-based)

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Algorithm-antagonistic Topology

• Simple topology with traffic flows that should
  expose a weakness to each topology

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Algorithm-antagonistic Topology
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Evaluation

• Simple Example
• Algorithm-antagonistic Topologies
• Large-scale Topology (PlanetLab-based)

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Planetlab as VPN-network source

• Large, distributed testbed
• We modelled the Overlay part of a fictional
  43-node corporate network using traces taken over
  planetlab
• The Intranet link topology was obtained from
  2-level clustering and eyeballing
• Traffic flows include a measured flow and a set
  of background and disruptive flows

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PlanetLab (UCLA-gtac.uk)
Packet Losses
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Conclusions

• Utilizing ISP connectivity enables balancing
  packet loss rate vs- end-to-end delays
• Dynamic algorithms can adapt to a variety of
  wide-area conditions
• Congestion prediction can help in certain
  environments, however local-only decision making
  works well
• Certain choke points must be identified so that
  synchronization effects will not occur
• Making better use of bandwidth can lower cost of
  deploying distributed corporate networks