Traffic Engineering

1. Traffic Engineering By Kavitha Ganapa

2. Introduction • Traffic engineering is concerned with the issue of performance evaluation and optimization of operational IP networks • Through carefully managing the traffic distribution inside a network • Congestion hot spots can be reduced • Resource utilization can be improved

3. Need for Traffic engineering • Need for service providers to efficiently provide and manage network resources to accommodate resource commitments • To meet customer’s expectation of guaranteed and differentiated services • To reduce cost of provisioning the services

4. Fish problem • Leads to extremely unbalanced traffic • Poor utilization of network resources

5. Fish problem in IP routing • Fish problem is caused by primarily two properties • IP routing is destination-based, all packets whose destination addresses share the same prefix have the same next hop • Decision making in current routing is based on local optimization

6. Traffic engineering solutions • Fish problem is solved by going beyond current destination based routing and by providing mechanisms to explicitly manage the traffic inside network • Overlay Model • Peer Model

7. Overlay Model • Calculates the routes for traffic demands for edge nodes • Service providers then set up MPLS explicit routes between edge routes and match traffic demands over them, creating a full-mesh network • Suffers from N-square problem, problems with scalability

8. Peer Model • Achieves balanced traffic distribution by manipulating link weights in the OSPF routing protocol • More scalable than Overlay Model • Packets are forwarded based on longest-prefix match • Eliminates N-square problem and reduces • Reduces messaging overheads in setting up explicit routes

9. Optimization objectives • Minimizing congestion and packet losses in the network • Network congestion is caused by • Inadequate network resources (can be solved by new capacity or reduce demands) • Unbalanced traffic distribution (can be addressed by better management of the resources in the network) • Improving link Utilization • Minimizing the total delay experienced by packets • Increasing the number of customers with the current assets

10. One objective • To minimize the maximum of link utilization • Why? • Hot spots are the points with the highest link utilization • Queuing delay increases nonlinearly as link utilization becomes higher • By minimizing the maximum of link utilization traffic is spread and the resources are efficiently used

11. Advantages of the Objective • Reduces the total delay experienced by the packets • Moves the traffic away from congested hot spots to less utilized parts of the network thus balanced traffic distribution • Leaves more space for future traffic growth, the percentage of residual bandwidth is maximized by the minimizing the maximum link utilization

12. Building blocks • Data repository • Topology and state discovery • Traffic demand estimation • Route computation (constraint-based routing) • Network interface • Graphic user interface • Topology and state discovery and constraint based routing are two critical components of traffic engineering

13. Topology and state discovery • OSPF-based scheme • Because OSPF is widely deployed • Has the necessary mechanisms for distributing link status and constructing a topology database • Extended link state information for traffic engineering • Local and remote interface IP addresses • Traffic engineering metric • Maximum bandwidth • Maximum reservable bandwidth • Unreserved bandwidth • Resource class

14. Constraint-based routing • Shortest path • Minimum hop • Minimize the total resource consumption per route • Shortest widest path • Avoids overloading by maximizing the residual capacity across the network • Hybrid algorithm • Combination of Shortest path/Minimum hop and shortest widest path

15. Multipath load sharing • Hashing based traffic splitting schemes • Direct hashing • Can split a load only into equal amounts • Table-based hashing • Can distribute the traffic as required

16. Summary • Traffic engineering is concerned with performance optimization of operational networks • Provides a set of tools for efficiently provisioning and managing backbone networks • Used to reduce congestion hot spots, improve overall utilization of networks and reduce the cost for meeting resource commitments to their customers

17. Research work • Our work includes the investigation of the QoS-based routing problem under two different frameworks: • the traditionally used SPC-QRF • The newly proposed SPD-QRF

18. Acknowledgments • The slides are prepared based on the information from Architectures and Mechanisms for Quality of Service by Zheng Wang