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Traffic Engineering and Routing
Hansen Bow
Topics
• 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
• 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
• 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
• 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
• 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
• 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
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