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Transcript of ida05.ppt
Traffic Engineering in IP NetworksTraffic Engineering in IP Networks
Jennifer RexfordComputer Science Department
Princeton University; Princeton, NJhttp://www.cs.princeton.edu/~jrex
A Little About Me…A Little About Me…
Technical interests: data networking– Network measurement
– Network operations
– Internet routing and infrastructure Job history
– 2005-onward: Professor in Computer Science at Princeton
– 1996-2005: AT&T Labs—Research» Technology transfer of tools for measurement, configuration,
troubleshooting, and traffic engineering to network operators
DARPA involvement– Member of the ISAT study group
– Knowledge Plane seedling project
– NetVision2012 workshops
OutlineOutline
Internet routing protocolsTraffic engineering using traditional protocols
– Optimizing configuration to the traffic
– Needs topology, routing, and traffic dataTraffic demands
– Volume of load between edges of the network
– Measuring the traffic demandsRoute optimization
– Tuning the link weights to the traffic
– Satisfying the operational constraintsConclusions
Internet ArchitectureInternet Architecture
Divided into Autonomous Systems– Regions of administrative control
– Routers and links managed by an institution
– Service provider, company, university, …Hierarchy of Autonomous Systems
– Tier-1 provider with nationwide backbone
– Medium-sized regional provider
– Campus or corporate networkInteraction between Autonomous Systems
– Internal topology is not shared
– … but, ASes interact to coordinate routing
Path Traversing Multiple ASesPath Traversing Multiple ASes
1
2
3
4
5
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ClientWeb server
Path: 6, 5, 4, 3, 2, 1
Interdomain Routing: Border Gateway ProtocolInterdomain Routing: Border Gateway Protocol
ASes exchange info about who they can reach– IP prefix: block of destination IP addresses
– AS path: sequence of ASes along the path
Policies configured by the AS’s network operator– Path selection: which of the paths to use?
– Path export: which neighbors to tell?
1 2 3
12.34.158.5
“I can reach 12.34.158.0/24”
“I can reach 12.34.158.0/24 via AS 1”
Intradomain Routing: OSPF or IS-ISIntradomain Routing: OSPF or IS-IS
Shortest path routing based on link weights– Routers flood the link-state information to each other
– Routers compute the “next hop” to reach other routers
Weights configured by the AS’s network operator– Simple heuristics: link capacity or physical distance
– Traffic engineering: tuning the link weights to the traffic
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Motivating Problem: Congested LinkMotivating Problem: Congested Link
Detecting that a link is congested– Utilization statistics suggest overloaded link
– Probe traffic suffers degraded performance
– Customers complain (via the phone network?)
Reasons why the link might be congested– Increase in the offered traffic
– Routing change due to equipment failure
– Routing change due to a change in another AS
Challenges– Know the cause, not just the manifestations
– Predict the effects of possible changes to link weights
Traffic Engineering in an ISP BackboneTraffic Engineering in an ISP Backbone
Network topology– Connectivity and capacity of routers and links
Traffic demands– Offered load between points in the network
Routing configuration– Link weights for selecting paths
Performance objective– Balanced load, low latency, …
Question: Given the topology and traffic demands in an IP network, what link weights should be used?
Modeling Traffic DemandsModeling Traffic DemandsVolume of traffic V(s,d,t)
– From a source s– To a destination d– Over a time period t
Time period– Performance debugging – minutes– Traffic engineering – hours or days– Network design – days to weeks
Sources and destinations– Hosts – interesting, but huge, and hard to measure– IP prefixes – still big, and not seen by any one AS – Edge routers – hmmm….
Traffic MatrixTraffic Matrix
in
out
Traffic matrix: V(in,out,t) for all pairs (in,out)
Problem: Hot Potato RoutingProblem: Hot Potato RoutingAS is in the middle of the Internet
– Multiple connections to multiple other ASes
– Egress point depends on intradomain routingProblem with point-to-point models
– Want to predict impact of changing intradomain routing
– But, a change in weights may change the egress point!
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Traffic Demand: Multiple Egress PointsTraffic Demand: Multiple Egress Points
Definition: V(in, {out}, t)– Entry link (in)
– Set of possible egress links ({out})
– Time period (t)
– Volume of traffic (V(in,{out},t))
Computing the traffic demands– Measure the traffic where it enters the ISP backbone
– Identify the set of egress links where traffic could leave
– Sum over all traffic with same in, {out}, and t
Traffic Mapping: Ingress MeasurementTraffic Mapping: Ingress Measurement
Packet measurement (e.g., Netflow, sampling)– Ingress point i
– Destination prefix d
– Traffic volume Vid
i dingress destination
Traffic Mapping: Egress Point(s)Traffic Mapping: Egress Point(s)
Routing data (e.g., forwarding tables)– Destination prefix d
– Set of egress points ed
ddestination
Traffic Mapping: Combining the DataTraffic Mapping: Combining the Data
Combining multiple types of data– Traffic: Vid (ingress i, destination prefix d)
– Routing: ed (set ed of egress links toward d)
– Combining: sum over Vid with same ed
iingress
egress set
Application on the AT&T BackboneApplication on the AT&T Backbone
Measurement data– Netflow data (ingress traffic)
– Forwarding tables (sets of egress points)
– Configuration files (topology and link weights)
Effectiveness– Ingress traffic could be matched with egress sets
– Simulated flow of traffic consistent with link loads
Challenges– Loss of Netflow records during delivery (can correct for it!)
– Egress set changes between table dumps (not very many)
– Topology changes between configuration dumps (just one!)
Three Traffic Demands in San FranciscoThree Traffic Demands in San Francisco
Underpinnings of the OptimizationUnderpinnings of the Optimization
Route prediction engine (“what-if” tool)– Model the influence of link weights on traffic flow
» Select a closest exit point based on link weights
» Compute shortest path(s) based on link weights
» Capture splitting over multiple shortest paths
– Sum the traffic volume traversing each link
Objective function– Rate the “goodness” of a setting of the link weights
– E.g., “max link utilization” or “sum of exp(utilization)”
Weight OptimizationWeight Optimization
Local search– Generate a candidate setting of the weights
– Predict the resulting load on the network links
– Compute the value of the objective function
– Repeat, keeping solution with lowest objective function
Efficient computation– Explore the “neighborhood” around good solutions
– Exploit efficient incremental graph algorithms
Incorporating Operational RealitiesIncorporating Operational Realities
Minimize configuration changes– Changing just one or two link weights is often enough
Tolerate equipment failures– Weights settings usually remain good after failure
– … or can be fixed by changing one or two weights
Limit the number of weight values– Small number of integer values is sufficient
Tolerate inaccuracy in the traffic demands– Good weights remain good after introducing random noise
Limit frequency of link-weight changes– Joint optimization for day and night traffic matrices
Application to AT&T’s Backbone NetworkApplication to AT&T’s Backbone Network
Performance of the optimized weights– Good solution within a few minutes
– Much better than traditional heuristics
– Competitive with multi-commodity flow solution
How AT&T changes the link weights– Maintenance done from midnight to 6am
– Predict effects of removing link(s)
– Reoptimize the link weights to avoid congestion
– Configure new weights before disabling equipment
ConclusionsConclusions
Our approach– Measure: network-wide view of traffic and routing
– Model: data representations and “what-if” tools
– Control: intelligent changes to operational network
Application in AT&T’s network– Capacity planning
– Customer acquisition
– Preparing for maintenance activities
– Comparing different routing protocols
Stepping Back: IP Network ManagementStepping Back: IP Network Management
Lessons learned– Good: network-wide views, control and objectives
– Bad: indirect control and non-real-time control
Next steps: Routing Control Platform– Direct, real-time control over the routing
– Network control entirely in the management system
– Routers just forward packets and provide measurements
– Initial prototype and results are very promising
– Platform for incremental deployment of secure protocols
To Learn More…To Learn More…
Traffic engineering overview– “Traffic engineering for IP networks”
(http://www.cs.princeton.edu/~jrex/papers/ieeenet00.ps)
– “Traffic engineering with traditional IP routing protocols”(http://www.cs.princeton.edu/~jrex/papers/ieeecomm02.ps)
Traffic measurement– "Measurement and analysis of IP network usage and behavior”
(http://www.cs.princeton.edu/~jrex/papers/ieeecomm00.ps)
– “Deriving traffic demands for operational IP networks”(http://www.cs.princeton.edu/~jrex/papers/ton01.ps)
Route optimization– “Internet traffic engineering by optimizing OSPF weights”
(http://www.ieee-infocom.org/2000/papers/165.ps)
– “Optimizing OSPF/IS-IS weights in a changing world”(http://www.research.att.com/~mthorup/PAPERS/change_ospf.ps)
Routing Control Platform– “The case for separating routing from routers”
(http://www.cs.princeton.edu/~jrex/papers/rcp.pdf)
– “Design and implementation of a Routing Control Platform”