Bandwidth Management and Scheduling in MPLS DiffServ Networks

1. Bandwidth Management and Scheduling in MPLS DiffServ Networks Anand Srinivasan Eion Ottawa, Canada Ximing Zeng, Chung-Horng Lung, Changcheng Huang Department of Systems and Computer Engineering Carleton University Ottawa, Canada

2. Outline • Diverse QoS Requirements • DiffServ Forwarding Classes • Cisco Solutions • Solutions based on fair queueing • Our Solution • Performance study

3. QoS requirements

4. QoS requirements for real time applications

5. QoS requirements for interactive applications

6. QoS requirements for streaming applications

7. DiffServ Service Classes • Expedited Forwarding (EF) PHB (RFC-2598) • Provides a low-loss, low-latency, low-jitter, and assured bandwidth service. Real-time applications such as voice over IP (VoIP), video, and online trading programs require such a robust network-treatment. • Assured Forwarding (AFxy) PHB (RFC-2597) • Provides certain forwarding assurance by allocating certain bandwidth and buffer space. Applications with certain QoS requirements but not real-time can use AF service. For example: streaming video. • Best Effort Service • No service guarantee except for a minimum bandwidth to prevent service starvation.

8. Cisco Solution • LLQ or MDRR High priority EF EF VoIP, Interactive Game… PQ AF1x Video Conferencing… AF2x Video on demand … CBWFQ Low priority AF and BE AF3x E-commerce … AF4x …… BE http,ftp, email… Total reservable bandwidth is about 75%. BE reservation fixed around 25%. EF traffic is constrained and should not exceed 33%; small queue and packet size. AFs reserve the rest bandwidth.

9. Cisco Solution EF is assigned a bandwidth less than 33% of the link speed and is constrained according to the assigned bandwidth. However burst of EF traffic still exists. BE reserves a certain amount of bandwidth. The rest of the bandwidth can be allocated to AF services. BE = 25% EF<33% AF4 AF3 AF1 AF2 AFs and BE may not always get their bandwidth as reserved !

10. bytes ρ delay delay backlog backlog σ r t Cisco Solution • Advantage:EF packets are guaranteed smallest delay possible by given them high priority. • Tradeoff: AF packets may be delayed due to burst of EF packets and cannot meet its desired delay bound! bytes t To minimize the impact EF brings to the AF classes: EF has small queue size (therefore, close to CBR) EF has small packet size (shorter waiting time for other packets)

11. Link rate Peak rate Reserved rate Average rate EF traffic rate t Cisco Solution • What if the EF traffic is bursty? A trade off has to be made! The actual bandwidth reserved to EF class should close to the peak rate to minimize the service impact. If bandwidth other than the average rate of EF traffic is claimed allocatable, then when EF burst comes, the bandwidth to AF classes cannot be guaranteed. Bad QoS! If bandwidth other than the peak rate of EF traffic is claimed allocatable, then AF QoS is guaranteed. Low bandwidth utilization!

12. Cisco Solution Under LLQ, to minimize the service impact to AF service Classes, EF bandwidth is Over-provisioned. EF average BE=25% EF wasted AF4 AF3 AF1 AF2

13. Other solutions • Assign each class certain bandwidth EF VoIP, Interactive Game… AF1x Video Conferencing… AF2x Video on demand … WFQ/ DWRR AF3x E-commerce … AF4x …… BE http,ftp, email…

14. r r delay delay Other solutions (WFQ) • Use weighted fair queueing to assign bandwidth to EF, AF and BE classes. • Advantage: Service to AF packets will not be affected by EF traffic, they always get their reserved bandwidth • Disadvantage: Over-provisioning is still needed to guarantee small delay to EF classes. ρ If EF traffic is bursty, to have a small delay, a large bandwidth reservation is needed, which causes the same problem of wasted bandwidth. σ

15. Other solutions (DWRR) • Dynamically adjust the bandwidth to EF class according to the backlog of EF traffic. The unused bandwidth can be used by BE traffic. • Advantage: the EF still gets a relatively low delay. • Practical problems: • 1)How often should we adjust the bandwidth allocation? • 2)If it is WFQ, how can we adjust the virtual finish time for all the backlogged packets on line? • 3)The bandwidth unused by EF can be used by BE, but is there any guaranteed minimum bandwidth? Or how can we assign the unused bandwidth?

16. Our Solution • Proposed scheduler architecture EF VoIP, Interactive Game… High priority PQ BE Low priority http,ftp, email… AF1x Video Conferencing… CBWFQ AF2x Video on demand … AF3x E-commerce … AF4x ……

17. Peak rate Reserved rate BE traffic rate Our Solution • EF and BE share the bandwidth: Link rate Average rate EF traffic rate t

18. BE traffic rate Our Solution • EF and BE share the bandwidth: Link rate Peak rate Reserved rate Average rate EF traffic rate t

19. EF + BE = rBE + Now free! AF4 AF3 AF1 AF2 The pie under our solution. You can have an extra slice! Our Solution rBE = 25% - AF4 AF3 AF1 AF2 The pie under WFQ or Cisco LLQ

20. Our Solution • Advantages: • EF is given no less (if not more) bandwidth than in WFQ. Performance is guaranteed. • AFs are guaranteed the same bandwidth, the same performance can be expected. • Bandwidth can be allocated to EF and AF users more efficiently! • Tradeoff: • BE traffic may experience a longer delay due to EF bursts. However, they are not delay sensitive and their average minimum throughput is still guaranteed.

21. Simulation result Src 0: EF traffic: 7 on-off voice sources 369 packets/sec in average. Src 1: BE traffic: 800 packets/sce, Exponential Src 2/3: AF traffic: 400 packets/sce, Exponential Link speed: 2000 packets/sce. Average load: 98.45%

22. Simulation result • EF delay under LLQ, DWRR and WPRR LLQ provides the smallest Delay to EF class. WPRR provides delay which is Comparable tp LLQ DWRR provides a much longer Delay.

23. Simulation result • AF delay under LLQ, DWRR and WPRR The same delay bound is Guaranteed under both DWRR And WPRR. Under LLQ, the AF delay is longer Due to the burstness of EF traffic. 6% of the packets violate the delay Bound.

24. Simulation result • BE throughput

25. Simulation result • BE throughput

26. Conclusion • We developed a new scheduler for DiffServ routers with the following advantage: • High bandwidth utilization • Guaranteed QoS • Guarantee small delay and loss for EF. • Provide QoS guarantee to AF by reserving the bandwidth. • Guarantee the minimum throughput of BE.

27. References • [1] S.Blake, D.Black, M.Carlson, E.Davies, Z.Zhang, W.Weiss, “An Architecture for Differentiated Services.” IETF RFC 2475. Dec 1998. • [2] V. Jacobson, K. Nichols, K. Poduri, “An Expedited Forwarding PHB.” IETF RFC 2598. June 1999. • [3] J. Heinanen, F. Baker, W. Weiss, J.Wroclawski, “Assured Forwarding PHB Group.” IETF RFC 2597. June 1999. • [4] J. Mao, W.M. Moh. B Wei, “PQWRR scheduling algorithm in supporting of DiffServ” 2001. ICC 2001. IEEE International Conference on Communications,Volume: 3 , Pages:679 – 684.11-14 June 2001. • [5] A.K.Parekh, R.G.Gallager, “A Generalized Processor Sharing Approach to Flow Control in Integrated Service Networks: The single node case,” IEEE/ACM Transactions on Networking, Pages:344 - 357. June 1993. • [6] H.Wang, C.Shen, K.G.Shin, “Adaptive-weighted packet scheduling for premium service” Communications, 2001. ICC 2001. IEEE International Conference on , Volume: 6 ,  Pages:1846 – 1850. 11-14 June 2001. • [7] F. Le Faucheur, L. Wu, B. Davie, S. Davari, P. Vaananen, R.Krishnan, P. Cheval, J. Heinanen, “Multi-Protocol Label Switching (MPLS) Support of Differentiated Services.” IETF RFC 3270 May 2002.  

28. Thank You !