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