the delta routing project low-loss routing for hybrid private networks
DESCRIPTION
The Delta Routing Project Low-loss Routing for Hybrid Private Networks. George Porter (UCB) Minwen Ji, Ph.D. (SRC - HP Labs). Outline. Motivation/overview of corporate networks Problem Statement Architecture Two layers: Physical and Overlay The Delta Protocol The Delta+TM Protocol - PowerPoint PPT PresentationTRANSCRIPT
The Delta Routing ProjectLow-loss Routing for Hybrid Private Networks
George Porter (UCB)
Minwen Ji, Ph.D. (SRC - HP Labs)
Outline
• Motivation/overview of corporate networks
• Problem Statement
• Architecture– Two layers: Physical and Overlay– The Delta Protocol– The Delta+TM Protocol
• Evaluation
• Conclusions
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
SFNYC
LON
LA
DC
DFW
ALX
SEA
HOU
OSPF
Corporate Network ConstructionOverlay Layer
• 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’
SFNYC
LON
LA
DC
DFW
ALX
SEA
HOU
ISP Connectivity
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
SFNYC
LON
LA
DC
DFW
ALX
SEA
HOU
Overlay / VPNTunnels
IntranetTopology
1
2
3
4
5
1
2
3
4
5
Architecture
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)
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.
Overlay Path Selection Algorithms
• Static– Lasthop– Nexthop– Random
• Dynamic– Delta
• Minimize end-to-end delay
– Delta+TM• Predict and avoid congestion by inferring global traffic matrix
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
Limitation of Delta Algorithm
• Since Delta uses local information, it might send traffic to an overloaded link:
congested
• Can we avoid this?
Delta+TM (Traffic Matrix)
• Key idea:– Don’t 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
Traffic Matrix Estimation
1 2 3 4
1 0.00 4.54 1.92 1.14
2 1.04 0.00 1.57 1.78
3 2.52 3.04 0.00 4.08
4 3.64 4.30 4.13 0.00
+ TopologyInformation =
.3
.6 1.2
.03
1.3
.89• Each node measures flows
that transit through it• Long-term averages are
flooded to fill in the entries of the table that a node can’t directly measure
Evaluation
1) Simple Example2) Algorithm-antagonistic Topologies3) Large-scale Topology (PlanetLab-
based)
Linear Topology
Congestion Event
Congestion Event
Evaluation
1) Simple Example2) Algorithm-antagonistic Topologies3) Large-scale Topology (PlanetLab-
based)
Algorithm-antagonistic Topology
• Simple topology with traffic flows that should expose a weakness to each topology
Algorithm-antagonistic Topology
Evaluation
1) Simple Example2) Algorithm-antagonistic Topologies3) Large-scale Topology (PlanetLab-
based)
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
PlanetLab (UCLA->ac.uk)
ppnonly 4,438
nexthop 2,492
lasthop 3,469
DeltaTM 3,523
Delta 4,443
Packet Losses
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