Guaranteed Quality-of-Service Access to IEEE 802.11 Wireless LANs

1. Guaranteed Quality-of-Service Access to IEEE 802.11 Wireless LANs Dr-Jiunn Deng Department of Electrical Engineering National Taiwan University, Taipei, Taiwan, R.O.C. Email: djdeng@cobra.ee.ntu.edu.tw October 29, 2002

2. "Nomadic computing, providing access while you're on the road so that the Internet services you see when you're someplace else are no different than what you have back in your office.“ --Leonard Kleinrock "Radio-based links into the Net will be very typical. If you have a question, you'll whip out your Palm Pilot with a radio link and go on the Net and pull the data out.“ --Vinton Cerf "Many sites in the research community will have access at gigabyte speed to the Internet. You'll see the increasing introduction of wireless access, so people don't have to feel tethered to the Net. And we're going to see increasing content.“ --Robert Kahn "The Internet will become the pervasive network for the world's telecom traffic. Voice and video will transfer over to it in the next five to 10 years. Clearly, you're going to have video on demand, radio or TV, that can have millions of different sources or special subjects that (small numbers) care about.“ --Lawrence Roberts The next wave of the Internet The Net's founders predict its future: Towards Multimedia Oriented Mobile Systems and providing “Anytime Anywhere Anyform” Information Systems

3. Status of specified wireless networking technologies IEEE 802.11 – keep growing Bluetooth – will see The rest – some need to be watched, most never take off

4. 802.11 WLAN Architecture Wired Network AP AP Basic Service Set

5. DIFS SIFS DIFS CW SIFS SIFS DIFS CW DIFS NAV (RTS) CW NAV (CTS) NAV (Data) Defer access Backoff time started Backoff time: DCF (CSMA/CA) RTS Data Source CTS ACK Destination Other

6. MAC Architecture Contention-free Service Contention Service Point Coordination Function (PCF) MAC Extent Distributed Coordination Function (DCF)

7. Superframe Superframe CFP CP CFP CP Stretched DCF period Contention Free Period Repetition Interval Contention Free Period Contention Period SIFS PIFS PIFS SIFS PIFS SIFS SIFS SIFS PCF Beacon CF-Poll CF-Poll CF-End Sta-to-Sta ACK Sta-to-Sta ACK NAV

8. Motivation • Packet-switched solutions that take advantage of silences in a given voice call by multiplexing voice data from other calls are more bandwidth-efficient than circuit-switched solutions • In wireless networks, where bandwidth is more constrained • DCF can not support service discipline of integrated multimedia traffic since it does not include any priority and access policy • PCF mode offers a “packet-switched connection-oriented” service, which is well suited for telephony traffic • In order to poll the stations an AP must maintain a polling list, which is implementation dependent The use of packet-switched techniques for carrying multimedia traffic in 802.11 WLANs are indeed needed

9. Bandwidth management and QoS • IETF groups are working on proposals including RSVP, Differentiated Services, and Integrated Services to provide better QOS control in IP networks • Principle 1: Marking of packets is needed to distinguish between different classes • Principle 2: provide protection (isolation) for one class from other classes • Principle 3: It is desirable to use resources as efficiently as possible • Principle 4: Application flow declares its needs, network may block call if it cannot satisfy the needs

10. AP Should we supported these functionalities in.. CLIENT? CORE? EDGE? Wired Network AP AP Basic Service Set

11. transmission A propagation B nodal processing queueing Delay in packet-switched networks

12. Enforcing priority for RA Too support priority, we change the backoff time generation function Consecutive times (i) Backoff slot numbers st nd rd th 1 2 3 4 Types of requests (k, m, n) Real-time handoff traffic 0 – 3 0 -7 0 – 15 0 – 31 ( 0, 1, 1 ) Admitted inactivated video traffic 4 – 7 8 - 15 16 – 31 32 - 63 ( 1, 1, 1 ) Non-real-time handoff traffic New request traffic 8 – 15 16 - 31 32- 63 64 – 127 ( 2, 2, 1 )

13. Adaptive contention window • The collision avoidance strategy in DCF avoids long access delays when the load is light, but it causes a high collision probability and channel utilization in degraded in bursty arrival or congested scenarios • In this paper, we propose an adaptive contention window mechanism to dynamically expand and contract the contention window size according to the current load and achieve the theoretical capacity limits. • Define the utilization factor • The value of utilization factor provides a lower bound to the actual number of stations trying to access the channel during the last contention window

14. Adaptive contention window • is a tight upper bound of in a system operating with the optimal channel utilization level • By fixing a given value for the frame size, the value of is almost constant • can be used as a measure of the network contention level when the network utilizes the optimal contention window size corresponding to the ongoing network and traffic configuration • We double the size of contention window when the utilization factor exceeds , but we halve the size of contention window when the utilization factor becomes less than , rather then

15. Token buffer for voice traffic Token buffer for video traffic Packet flow Control flow Request flow Packet scheduling policy in CFP Contention Free Period Repetition Interval Contention Period Contention Free Period PIGGY-BACKING OF REQUEST Request Packet-Transmission Permission CSMA/CA with ENFORCING PRIORITY for RA PACKET-TRANSMISSION CHANNEL

16. Packet scheduling policy in CFP 1)The PBS first scans the token buffers of voice sources according to the preset priority order. If a token is found, it removes one token from this token buffer and transmits a packet for this voice source. Then, the PBS generates next token for this voice source after second if the piggybacking was set while transmitting the packet, where is the time to transmit a packet. 2)If no tokens are found in the token buffers of voice sources, the PBS continues to scan the token buffers for video sources according to the preset priority order. If a token is found, it transmits a packet for this video source. And it will not remove the token if the piggybacking was set while transmitting this packet. If the piggybacking was not set and it is not the last packet (End-of-File) either, the PBS removes the token, and then generates next token for this video source after seconds. But if this admitted inactivated video source contended successfully within seconds, there is not any toke be generated by PBS automatically. 3)If there is no token found in all token buffers. The AP uses the CF-END frame to announce the end of the contention free period and the maximum time interval of following contention period.

17. Admission Control for voice traffic • Let , If and for all =1,2…, , then all the packets generated by new-call voice sources meet their jitter constraints. Furthermore, if and for sources which is handoffed from other cells, then the packet generated by the source after handoff meets its jitter constraint.

18. Admission Control for video traffic • Let , , , , and , where . If and for all , then the delay constraints are satisfied for all the new-call video sources. Furthermore, if for source which is handoff from other cells, then the packet generated by the source after handoff meets its delay constraint.

19. CFP-channel I CFP-channel II CP-channel III Adaptive Bandwidth Allocation Strategy Contention Free Period Repetition Interval Contention Free Period Contention Period Channel I for new-call/handoff voice/video traffic Channel II for handoff voice/video traffic Channel III for data traffic

20. Adaptive Bandwidth Allocation Strategy IFmonitored dropping probability > threshold_D THEN IFbandwidth utilization < THEN size of allocated bandwidth II= min {max {size of allocated bandwidth I, size of allocated bandwidth II} up_ , total bandwidth } ELSE size of allocated bandwidth II= min {max {size of allocated bandwidth I, size of allocated bandwidth II} up_ , total bandwidth threshold_up_II } ELSE

21. Adaptive Bandwidth Allocation Strategy (cont.) IFmonitored blocking probability > threshold_B THEN IFbandwidth utilization < THEN size of allocated bandwidth I= min {size of allocated bandwidth I up_ , total bandwidth threshold.1_up_I } ELSE size of allocated bandwidth I= min {size of allocated bandwidth I up_ , total bandwidththreshold.2_up_I } ELSE IFbandwidth utilization < THEN size of allocated bandwidth II= max {size of allocated bandwidth II down_ , total bandwidththreshold_down_II } size of allocated bandwidth I= max {size of allocated bandwidth I down_ , total bandwidththreshold_down_I }

22. Conclusions • The design of priority-sensitive network protocols continues to be an important problem • Broadband wireless links constitute a subclass where prioritization is key to optimizing overall performance • We proposed a pragmatic non-preemptive priority based access control scheme built on well-know protocols and offered easily implemented and yet flexible criteria for traffic prioritization in a wireless environment. • Various QoS requirements are needed in the future • Multilevel priorities, bandwidth allocation, connection admission control, and traffic policing all need to be considered together in the future networks

23. Reference • D. J. Deng and R. S. Chang, “A Priority Scheme for IEEE 802.11 DCF Access Method,”IEICE Trans. Commun., vol. E82-B, no. 1, pp. 96-102, January 1999. • D. J. Deng and R. S. Chang, “A Non-Preemptive Priority Based Access Control Scheme for Broadband Ad-Hoc Wireless ATM Local Area Networks,” IEEE Journal on Selected Areas of Communications, Vol. 18, no. 9, Sep. 2000, pp. 1731-1739.