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A Practical Approach for Providing QoS: MPLS and DiffServ

A Practical Approach for Providing QoS: MPLS and DiffServ. Thomas Telkamp Director Data Architecture and Technology Global Crossing Telecommunications, Inc. telkamp@gblx.net. MPLS Maximizing the Performance and Profitability of Optical and Data Networks July 12 - 13, 2001 Dublin, Ireland.

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A Practical Approach for Providing QoS: MPLS and DiffServ

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  1. A Practical Approach for Providing QoS: MPLS and DiffServ Thomas Telkamp Director Data Architecture and Technology Global Crossing Telecommunications, Inc. telkamp@gblx.net MPLSMaximizing the Performance and Profitability of Optical and Data Networks July 12 - 13, 2001 Dublin, Ireland

  2. Agenda • Global Crossing MPLS deployment • Quality of Service? • A Practical Approach • Network Design and Capacity Planning • Differentiated Services • MPLS for Traffic Engineering • Fast Reroute and Per-Class TE • Queuing and Scheduling • Conclusion

  3. Global Crossing IP Backbone Network PEC AC-2 AC-1 North American Crossing PC-1 MAC EAC PAC SAC Based on announced network

  4. GBLX MPLS Deployment • Operational since 2Q 1999 • Traffic Engineering • IP TTL issues • Worldwide MPLS mesh 1Q 2001 • Currently over 6000 LSPs • Network: • Cisco and Juniper routers • OC-48 wavelengths • Covering Asia, US, South America and Europe • New Services: VPN (L2/L3)

  5. MPLS Traffic Engineering

  6. Quality of Service?Based on a paper with XiPeng Xiao (Photoris, Inc.) and Lionel M. Ni (Michigan State University) • Best Effort (e.g. Internet) • Real-time/Mission-critical traffic (e.g. Voice) • Increase revenue by value-added services • Two extremes: • Overprovisioning of bandwidth without additional mechanisms • Sophisticated mechanisms such as per-flow classification/policing/queuing and scheduling

  7. What Causes Problems? • Overloaded servers, or access to servers • Web, E-mail, etc. • TCP stack implementations • Link failures • fiber cuts • transmissions equipment failures • Router failures • complex software • early deployment of features • configuration

  8. A Practical Approach • Good Network Design • Differentiated Services (DiffServ) • Traffic Engineering • Traffic Protection (Fast Reroute) • Class-based Queuing • Not: • Extremely complex schemes (e.g. per-flow) • affecting equipment reliability • difficult to configure and manage

  9. Network Design • Avoid single points of failure • No bottlenecks in normal condition • Overprovisioning • with use of TE network can handle all traffic, even when the most critical links fails • Routing (IGP and BGP) • Security and Denial of Service attacks • Capacity Planning

  10. Differentiated Services • How many classes? • What are the targeted applications for each class? • Can end users distinguish between classes? • Example: • Class 1: Real-time • application: voice • Class 2: Assured • application: trading, non-interactive audio and video • Class 3: Best Effort • application: Internet

  11. MPLS Deployment • Traffic Engineering • Avoid congestion caused by uneven traffic distribution • Macro control • Constraint based LSP setup • Two LSP meshes: • Real-time traffic vs Assured/Best Effort • Classification based on interface or multi-field lookup • Different metrics • LSP Hierarchy • Scalability and VPNs

  12. MPLS LSP Deployment

  13. Traffic Protection • IGP convergence (OSPF/IS-IS) takes seconds • But can be improved by timer and SPF tuning • see Packet Design paper • MPLS Fast Reroute • Link or Node protection • Pre-configured patch LSPs (sub-optimal) • Use for real-time traffic only, or for all traffic (based on implementation)

  14. MPLS Fast Reroute • Protecting router switches traffic to pre-configured patch LSP after failure detection (fast) • Ingress router reroutes LSP (slow)

  15. Per-Class Traffic Engineering • Avoid concentration of real-time traffic at any link • Set upper limit on bandwidth reservations per class • E.g. max. 40% of a link for VoIP traffic • IETF Internet Draft(s) on ‘Diff-Serv-aware MPLS Traffic Engineering’ (Francois Le Faucheur, et al.)

  16. Class-based Queuing • Prefer ‘higher’ classes during congestion • sub-optimal fast-reroute period • major failures • Different queuing/scheduling mechanisms • Strict Priority Queuing • Jitter control for EF traffic • WRR/WFQ • and combinations • Configuration issues...

  17. Random Early Detection • Buffer Management • prevent tail-drop • TCP oscillations and synchronization • RED drops based on average queue length • WRED drops with different probability for each class • Only during congestion • Not used to guarantee bandwidth!

  18. Conclusion • Use combination of good network design, over-provisioning and MPLS/DiffServ • Use Traffic Engineering to prevent congestion • Use fast reroute and priority queuing for real-time traffic • Use WRR/WFQ to differentiate between Assured and Best Effort traffic • Too complex and too many features will make the network unreliable/unstable

  19. Questions?

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