Traffic Engineering and Routing
Hansen Bow
Topics
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Traffic Engineering with MPLS
Issues Concerning Voice over IP
Features of Netscope
QoS Routing for High-Speed Networks
QoS Routing for Multimedia
Traffic Engineering with MPLS:
Methods
• MPLS – multiprotocol label switching
• Constraint-based routing
• Enhanced link state IGP
MPLS-multiprotocol label
switching
• forwarding scheme
• at ingress of MPLS network, IP packets are
classified, tagged, and routed
• at next router, tag is used to determine
destination
• before leaving, tag is removed
Constraint-Based Routing
• computes bounded routes
• reservable bandwidth of a link is an
approximation
• can be done online or offline
Enhanced Link State IGP
(interior gateway protocol)
• distribute link information
• flood network to obtain information
Deploying MPLS System
(GlobeCenter)
• Statistics Collection
• Deploy LSP (label-switched path) with
bandwidth constraint
• Periodic update of LSP Bandwidth
• Offline Constraint-Based Routing
Voice over IP Issues
• modify capacity management and routing
methods in IP to support IP telephony
– delay less than 300ms
– loss rate <1%
• First Model: RSVP
• Second Model: voice service uses Virtual
Private Network
RSVP Routing
• Shortest Path First
• Shortest Available Path First
• Widest Available Path First
Virtual Private Networks
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interconnects telephony switches
Direct Path Only
Success to the Top
State-Dependent Routing
Approximate State-Dependent Routing
Direct and Alternate Routing
Policies
Differently Routed Calls with
Trunk Reservation
Routing Policies with Integrated
Services Model
• not much difference between SPF, SAPF,
WAPF
• fewer blocked calls for a given network
capacity because of better sharing of
network capacity
Features of Netscope
• traffic measurement and network modeling
• provide global views of configuration and
useage data
Utility of Netscope
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realizing customer SLAs
tuning parameters of network components
unite configuration
experiment with possible solutions to
variable complex traffic
Data
• Network components
• Modeling Traffic
• Routing
– multiple shortest paths
Visualization
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Objects
Statistics
Traffic and Links
Changing Routes
QoS Routing Issues for High
Speed Networks
• Goals
– satisfy QoS requirements for admitted
connection
– global efficiency
• Classes
– Source routing
– Distributed routing
– Hierarchical routing
Routing
• Collection of State Information
– local and global state
– aggregated global state
Routing
• Finding Feasible Path
– Unicast
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link optimization
link constrained
path optimization
path constrained
– Dijkstra’s algorithm
• http://www.cs.uwa.edu.au/undergraduate/courses/230.300/read
ings/graphapplet/graph.html
– Multicast
• Steiner Tree
Routing Strategies
• Source routing
– centralized problem, loop-free
– need global state, computation overhead
• Distributed routing
– routing response faster, scalable
– need global state, more messages, loops
• Hierarchical routing
– scales well, computation shared
– imprecision because aggregate state, complicated with
constraints,
Future Directions
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Efficient Routing Algorithms
Routing with imprecise state information
Multipath Routing
Rerouting
QoS Routing for Multimedia
• Metric Selection
– Efficient algorithms must exist for path
computation
– Reflect basic information of network
– orthogonal
• Multiple Metrics
– additive, multiplicative, concave
Bandwidth and Delay as Metrics
• finding path subject to two or more additive
and multiplicative metrics is NP-complete
• only feasible combination is bandwidth and,
for example, delay
Path Computation Algorithms
• Source Routing
• Hop-by-hop
– compute best path to every destination
– shortest-widest path is free of loops
References
• “NetScope: Traffic Engineering for IP Networks,” A. Feldmann, A.
Greenberg, C. Lund, N. Reingold, and J. Rexford, IEEE Network,
Mar./Apr. 2000, pp. 11-19
• “Traffic Engineering with MPLS in the Internet,” X. Xiao, A. Hannan,
B. Bailey, and L.M. Ni, Ibid., pp. 28-33
• “Capacity Management and Routing Policies for Voice over IP
Traffic,” P.P. Mishra, and H. Saran, Ibid, pp. 20-27
• “Quality-of-Service Routing for Supporting Multimedia Applications,”
Z. Wang, and J. Crowcroft, IEEE Journal on Selected Areas in
Communications, Vol. 14, No. 7, Sept. 1996
• “An Overview of Quality of Service Routhing for Next-Generation
High-Speed Networks: Problems and Solutions,” S. Chen and K.
Nahrstedt, IEEE Network, Nov./Dec. 1998, pp. 64-79