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Distributed Control Algorithms for Service Differentiation in Wireless Packet Networks

Distributed Control Algorithms for Service Differentiation in Wireless Packet Networks. INFOCOM 2001 Michael Barry, Andrew T. Campbell Andras Veres. Outline . Introduction Modified MAC Virtual MAC & Virtual Source algorithms Virtual Delay Curves Conclusions. Introduction.

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Distributed Control Algorithms for Service Differentiation in Wireless Packet Networks

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  1. Distributed Control Algorithms for Service Differentiation in Wireless Packet Networks INFOCOM 2001 Michael Barry, Andrew T. Campbell Andras Veres

  2. Outline • Introduction • Modified MAC • Virtual MAC & Virtual Source algorithms • Virtual Delay Curves • Conclusions

  3. Introduction • Wireless communications are becoming an essential feature of everybody’s life.

  4. Introduction(cont’d) • There are two principal approaches to support better than best-effort services for Internet based services in a future wireless network: 1. Conventional circuit switched paradigm 2. Wireless LAN protocols such as IEEE 802.11 (PCF), etc.

  5. Introduction(cont’d) • In this paper, we discuss the components of a differentiated services capable wireless network: 1. A distributed DiffServ capable wireless MAC 2. A distributed radio resource monitoring mechanism 3. Localized management of service level specifications and admission control 4. Fast mobility support in the access network

  6. Introduction(cont’d) • The proposed modified MAC is based on the IEEE 802.11 radio MAC algorithm for mobile hosts and base stations. • Providing service differentiation solely at the radio interface is insufficient to enable predictable behavior for individual traffic types.

  7. Modified MAC • The ideal MAC is adaptive and robust to both internal and external circumstances. • Use Backoff timer to achieve the service differentiation!!

  8. Modified MAC(cont’d) • Backoff times are set to a random value in the range [ 0 , CW] * Tslot • By decreasing the CWmax for a service class, the maximum backoff time can be limited during congestion. • This limits the range of congestion control, thus we trade lower delay for increased collision probability, and eventually larger packet loss ratio.

  9. Simulation Results of the Modified MAC • In the simulation, the traffic mix consisted of 5 voice traffics and 10 best effort traffics. • For high priority traffic: CWmin : [8, 32] ; CWmax : 64 • For best effort traffic: CWmin : [32, 128] ; CWmax : 1024

  10. Simulation Results of the Modified MAC(cont’d)

  11. Simulation Results of the Modified MAC(cont’d) • Channel load is increased by adding a new voice, video • and TCP session periodically every 5 seconds {16, 64}

  12. Simulation Results of the Modified MAC(cont’d)

  13. Virtual MAC & Virtual Source Algorithms • Although the modified MAC ensures effective service differentiation. However, it is not sufficient to ensure that high priority traffic gets better service than best effort traffic. • In most cases applications require absolute and not relative service quality. • The channel status is also important for different type of traffic!!

  14. Virtual MAC & Virtual Source Algorithms(cont’d) • In what follows, we present the Virtual MAC and Virtual Source algorithms that are capable of passively observing the radio channel. • This passive monitoring capability allows a mobile host to evaluate the state of the channel, and estimate the level of service it would receive without actually loading the channel.

  15. Virtual MAC & Virtual Source Algorithms(cont’d) • The channel can be in one of the three states: throughput limited, delay limited, or not congested. • These algorithms are operate in parallel to the real applications and MAC layer in the host and estimate the service level of the channel.

  16. Virtual MAC & Virtual Source Algorithms(cont’d) VS Application Interface buffer TCP/IP VMAC MAC PHY

  17. Virtual MAC & Virtual Source Algorithms(cont’d)

  18. Virtual MAC & Virtual Source Algorithms(cont’d)

  19. Virtual Delay Curves • The delay experienced by an application is made up of several components: packetization delay, delay accumulated in the buffers and the delay caused by the wireless MAC. • For the same data rate: psize* prate = const whereprateis the packet inter-arrival time psizeis the size of the application level packet

  20. Virtual Delay Curves(cont’d) • Define d(prate) as the virtual delay curve of an application. • The mobile hosts and the base stations runs VS algorithms with several prate. • Similarly, it can define the virtual delay variance curve v(prate) which calculates the virtual delay variances.

  21. Virtual Delay Curves(cont’d) Virtual Delay Curves Virtual Delay Variance Curve

  22. Admission Control • Based on the VS and VMAC results, an admission control(AC) algorithm can determine whether the channel can support a new traffic stream or not. • Simulation environment: • In the simulations, new voice sessions is accepted if the estimated average delay less than 10 ms, with the CW value of {32, 64}. (BS): 10 (MH): 100 400m

  23. Admission Control(cont’d)

  24. Admission Control(cont’d)

  25. Conclusions • This paper has shown how service differentiation can be provided in a mobile access network. • We have proposed two passive radio channel monitoring algorithms: VS and VMAC for estimating the achievable level of service without actually loading the channel

  26. Discussions • In the case of MHs have packets to transmit simultaneously, and they don’t transmit before then, thus it would be a serious collision and a wrong virtual delay curve for each of the MH which wants to transmit. • The curves may be different with the real channel status because of the virtual detection of the radio. • The high priority traffic should be transmit than low priority traffic rather than the reverse way!!

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