Wireless VoIP C3 R94922096  謝明龍 R94922088  關尚儒
Outline <ul><li>Problems to use VoIP on wireless network </li></ul><ul><li>Voice over WLAN </li></ul><ul><ul><li>MAC metho...
VoIP on Wireless Network <ul><li>Wireless network – lower speed , noise </li></ul><ul><ul><li>Upgrade physical speed , red...
Voice over WLAN
802.11 supplements glossary <ul><li>802.11a – 5GHz OFDM PHY layer  </li></ul><ul><li>802.11b – 2.4GHz CCK PHY layer  </li>...
802.11 standards 802.11  PHY 802.11  MAC supplements 802.11a, 802.11b and 802.11g supplements 802.11d, 802.11e, 802.11i an...
PHY    802.11n <ul><li>2.4GHz+5GHz (a/b/g) </li></ul><ul><li>MIMO+OFDM  </li></ul><ul><ul><li>MIMO (Multiple-In, Multiple...
MIMO
IEEE 802.11 MAC
Hidden Node Problem
Dual Queue Strategy
Dual Queue Strategy <ul><li>The 802.11e MAC implementation cannot be done by just upgrading the firmware of an existing MA...
Dual Queue Strategy <ul><li>above  802.11 the MAC controller  </li></ul><ul><ul><li>Original NIC driver    FIFO queue </l...
Dual Queue Strategy
VOIP AND ADMISSION CONTROL <ul><li>VoIP  </li></ul><ul><ul><li>codec    G.711 </li></ul></ul><ul><ul><ul><li>64 kbps stre...
VOIP AND ADMISSION CONTROL <ul><li>VoIP Admission Control </li></ul><ul><ul><li>assumptions </li></ul></ul><ul><ul><ul><li...
VOIP AND ADMISSION CONTROL <ul><li>VoIP packet transmission time ≒  981μs </li></ul><ul><ul><li>VoIP MAC packet transmissi...
VOIP AND ADMISSION CONTROL <ul><li>Every VoIP sessioin </li></ul><ul><ul><li>inter-active      2 senders </li></ul></ul><...
COMPARATIVE PERFORMANCE EVALUATION <ul><li>Using the ns-2 simulator </li></ul><ul><ul><li>802.11b PHY  </li></ul></ul><ul>...
COMPARATIVE PERFORMANCE EVALUATION
EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>...
 
Observation <ul><li>Compare to our Evaluation </li></ul><ul><ul><li>packet drop rate </li></ul></ul><ul><li>50 packets for...
EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>...
 
Observation <ul><li>Effect of queue size </li></ul>
EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>...
 
Observation <ul><li>worst case delay 11ms </li></ul><ul><ul><li>Queuing delay with the single queue </li></ul></ul><ul><ul...
EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>...
 
Observation <ul><li>Unfairness  </li></ul><ul><ul><li>between upstream and downstream TCP flows with the queue sizes of 50...
EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>...
 
Observation <ul><li>Delay of downlink voice packets </li></ul><ul><ul><li>increases linearly proportional to the MAC HW qu...
Brief Summary <ul><li>Driver of the 802.11 MAC controller </li></ul><ul><li>Strict priority queuing </li></ul><ul><li>Bott...
VoIP and 802.11e QoS standards
What’s the difference between Wireless/Wired VoIP? <ul><li>Mobility </li></ul><ul><ul><li>Roaming </li></ul></ul><ul><li>S...
Hidden Node Problem
Quality of Service <ul><li>QoS problems </li></ul><ul><li>802.11e QoS standard </li></ul><ul><li>A non-standard solution –...
QoS Problems <ul><li>Dropped Packets </li></ul><ul><li>Delay </li></ul><ul><li>Jitter </li></ul><ul><li>Out-of-order Deliv...
Quality of Service <ul><li>QoS problems </li></ul><ul><li>802.11e QoS standard </li></ul><ul><li>A non-standard solution –...
IEEE 802.11e <ul><li>A draft standard of July 2005 </li></ul><ul><li>It defines a set of QoS enhancements for WLAN applica...
Coordination Function <ul><li>For stations to decide which one has the right to deliver its packets </li></ul><ul><li>802....
Original 802.11 MAC <ul><li>Distributed Coordination Function (DCF) </li></ul><ul><li>Point Coordination Function (PCF) </...
Distributed Coordination Function (DCF) <ul><li>Share the medium between multiple stations </li></ul><ul><li>Rely on CSMA/...
How DCF works?
DCF Limitations <ul><li>When many collisions occur, the available bandwidth will be lower </li></ul><ul><li>No notion of h...
Original 802.11 MAC <ul><li>Distributed Coordination Function (DCF) </li></ul><ul><li>Point Coordination Function (PCF) </...
Point Coordination Function (PCF) <ul><li>Available only in &quot;infrastructure&quot; mode </li></ul><ul><li>Optional mod...
How PCF works?
802.11 MAC Layer Framework
802.11e MAC Protocol Operation <ul><li>Enhanced DCF (EDCF) </li></ul><ul><li>Hybrid Coordination Function (HCF) </li></ul>
Enhanced DCF (EDCF) <ul><li>Define Traffic Classes </li></ul><ul><li>High priority traffic has a higher chance of being se...
802.11e MAC Protocol Operation <ul><li>Enhanced DCF (EDCF) </li></ul><ul><li>Hybrid Coordination Function (HCF) </li></ul>
Hybrid Coordination Function (HCF) <ul><li>Works a lot like the PCF </li></ul><ul><li>Main difference with the PCF: Define...
What’s the difference between Wireless/Wired VoIP? <ul><li>Quality of Service </li></ul><ul><li>Security </li></ul><ul><li...
IEEE 802.11i <ul><li>The draft standard was ratified on 24 June 2004 </li></ul><ul><li>Supersede Wired Equivalent Privacy ...
IEEE 802.11i (cont.) <ul><li>802.1X for authentication (entailing the use of EAP and an authentication server) </li></ul><...
The Four-Way Handshake
What’s the difference between Wireless/Wired VoIP? <ul><li>Quality of Service </li></ul><ul><li>Security </li></ul><ul><li...
IEEE 802.11f & 802.11r <ul><li>802.11f: Inter-Access Point Protocol </li></ul><ul><li>802.11r: Fast roaming </li></ul>
Conclusion
Paper References 1 <ul><li>Jeonggyun Yu, Sunghyun Choi, Jaehwan Lee,  “Enhancement of VoIP over IEEE 802.11 WLAN via Dual ...
Paper Reference 2 <ul><li>Experimental VoIP capacity measurements for 802.11b WLANs </li></ul><ul><li>Enhancement of VolP ...
Web Site References <ul><li>http://www.ieee.or.com/Archive/80211/802_11e_QoS_files/frame.htm </li></ul><ul><li>http://en.w...
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  • 我想大家最關心的問題,就是,到底 Wireless VoIP 跟有線的 VoIP ,它們的差別在哪裡 最大的差別,當然就是 Wireless 沒有網路線;換句話說,就是傳輸介質的差異 而傳輸介質的差異,又可以演變成三個層次的問題:一,移動性,二,安全性,三, QoS 一,移動性的問題:我們是不是可以期待, Wireless VoIP ,有一天可以取代現在的 2.5G 和 3G Network ,而 Skype 可以取代中華電信,然後我們可以藉由某種 device 來達到隨時隨地,免費通話的效果?當然現在還是不可能啦 二,當我們使用 Wireless VoIP 時,另一個會想到的問題,就是安全性問題;因為 Wireless ,所以你無法得知,你的 Wireless Network 上,其它使用者在哪裡,如果有人蓄意攔截這個網路上的封包,你的通話是不是有可能會被竊聽 三, QoS ,這個問題比較複雜,因為在有線網路,已經有很完善的 QoS 機制,我們利用網路線上的電壓變化,就可以知道網路上 packet 的傳輸,是不是發生了 collision 但是在無線網路上,我們很難對空氣來作碰撞偵測的工作;原因在於 1. 無線電波在空氣中行進時 , 訊號的強度會隨距離增加而衰減 , 造成發送訊號時與接收訊號時感知的強度差異很大。 2. 有隱藏節點 (Hidden Node) 的問題。
  • C3.ppt

    1. 1. Wireless VoIP C3 R94922096 謝明龍 R94922088 關尚儒
    2. 2. Outline <ul><li>Problems to use VoIP on wireless network </li></ul><ul><li>Voice over WLAN </li></ul><ul><ul><li>MAC method </li></ul></ul><ul><ul><ul><li>802.11e </li></ul></ul></ul><ul><ul><ul><li>Dual queue scheme </li></ul></ul></ul><ul><li>VoIP and 802.11x standards </li></ul>
    3. 3. VoIP on Wireless Network <ul><li>Wireless network – lower speed , noise </li></ul><ul><ul><li>Upgrade physical speed , reduce noises (PHY) </li></ul></ul><ul><ul><li>Real-time packet prioritize (MAC) </li></ul></ul><ul><li>1AP-to-many Station </li></ul><ul><ul><li>Upgrade the capacity of single AP </li></ul></ul><ul><ul><li>Admission control </li></ul></ul><ul><li>Roaming </li></ul><ul><li>Mobile device power </li></ul><ul><li>Wireless security </li></ul>
    4. 4. Voice over WLAN
    5. 5. 802.11 supplements glossary <ul><li>802.11a – 5GHz OFDM PHY layer </li></ul><ul><li>802.11b – 2.4GHz CCK PHY layer </li></ul><ul><li>802.11c – bridging tables </li></ul><ul><li>802.11d – international roaming </li></ul><ul><li>802.11e – quality of service MAC </li></ul><ul><li>802.11f – inter-access point protocols </li></ul><ul><li>802.11g – 2.4GHz OFDM PHY </li></ul><ul><li>802.11h – European regulatory extensions </li></ul><ul><li>802.11i – enhanced security </li></ul><ul><li>802.11n – MIMO ODFM PHY </li></ul>
    6. 6. 802.11 standards 802.11 PHY 802.11 MAC supplements 802.11a, 802.11b and 802.11g supplements 802.11d, 802.11e, 802.11i and 802.11h supplements 802.11c and 802.11f higher layers
    7. 7. PHY  802.11n <ul><li>2.4GHz+5GHz (a/b/g) </li></ul><ul><li>MIMO+OFDM </li></ul><ul><ul><li>MIMO (Multiple-In, Multiple-Out) </li></ul></ul>
    8. 8. MIMO
    9. 9. IEEE 802.11 MAC
    10. 10. Hidden Node Problem
    11. 11. Dual Queue Strategy
    12. 12. Dual Queue Strategy <ul><li>The 802.11e MAC implementation cannot be done by just upgrading the firmware of an existing MAC controller chip only </li></ul><ul><li>It is difficult to Upgrade (replace) the existing APs </li></ul>
    13. 13. Dual Queue Strategy <ul><li>above 802.11 the MAC controller </li></ul><ul><ul><li>Original NIC driver  FIFO queue </li></ul></ul><ul><ul><li>New NIC driver  RT + NRT queue </li></ul></ul><ul><li>Strict priority queuing </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    14. 14. Dual Queue Strategy
    15. 15. VOIP AND ADMISSION CONTROL <ul><li>VoIP </li></ul><ul><ul><li>codec  G.711 </li></ul></ul><ul><ul><ul><li>64 kbps stream </li></ul></ul></ul><ul><ul><ul><li>8-bit pulse coded modulation (PCM) </li></ul></ul></ul><ul><ul><ul><li>sampling rate : 8000 samples/second </li></ul></ul></ul><ul><ul><li>A VoIP Packet per 20ms </li></ul></ul><ul><li>160-byte DATA + 12-byte RTP header + 8-byte UDP header+ 20-byte IP header + 8-byte SNAP header </li></ul><ul><li>= 208 bytes per VoIP packet </li></ul>
    16. 16. VOIP AND ADMISSION CONTROL <ul><li>VoIP Admission Control </li></ul><ul><ul><li>assumptions </li></ul></ul><ul><ul><ul><li>ACK Packet transmitted with 2Mbps </li></ul></ul></ul><ul><ul><ul><li>Long PHY preamble </li></ul></ul></ul><ul><ul><li>Packet transmission MAC </li></ul></ul><ul><ul><ul><li>DIFS deference </li></ul></ul></ul><ul><ul><ul><li>Backoff </li></ul></ul></ul><ul><ul><ul><li>Packet transmission </li></ul></ul></ul><ul><ul><ul><li>SIFS deference </li></ul></ul></ul><ul><ul><ul><li>ACK transmission </li></ul></ul></ul>
    17. 17. VOIP AND ADMISSION CONTROL <ul><li>VoIP packet transmission time ≒ 981μs </li></ul><ul><ul><li>VoIP MAC packet transmission time </li></ul></ul><ul><ul><ul><li>192-μs PLCP preamble/header + (24-byte MAC header + 4-byte CRC-32 + 208-byte payload) / 11 Mbits/s = 363 μs </li></ul></ul></ul><ul><ul><li>ACK transmission time at 2 Mbits/s </li></ul></ul><ul><ul><ul><li>192-μs PLCP preamble/header + 14-byte ACK packet / 2Mbits/s = 248 μs </li></ul></ul></ul><ul><ul><li>Average backoff duration </li></ul></ul><ul><ul><ul><li>31 (CWmin) * 20 μs (One Slot Time) / 2 = 310 μs </li></ul></ul></ul>
    18. 18. VOIP AND ADMISSION CONTROL <ul><li>Every VoIP sessioin </li></ul><ul><ul><li>inter-active  2 senders </li></ul></ul><ul><ul><li>one voice packet transmitted every 20ms </li></ul></ul><ul><li>Every 20ms time interval </li></ul><ul><ul><li>20 (= 20 ms / 981 μ s) voice packets </li></ul></ul><ul><li>Maximum number of VoIP sessions over a 802.11 LAN is 10 </li></ul>
    19. 19. COMPARATIVE PERFORMANCE EVALUATION <ul><li>Using the ns-2 simulator </li></ul><ul><ul><li>802.11b PHY </li></ul></ul><ul><ul><li>Traffic </li></ul></ul><ul><ul><ul><li>Voice  two-way constant bit rate (CBR) session according to G.711 codec </li></ul></ul></ul><ul><ul><ul><li>Data  unidirectional FTP/TCP flow with 1460-byte packet size and 12-packet (or 17520-byte) receive window size. </li></ul></ul></ul>
    20. 20. COMPARATIVE PERFORMANCE EVALUATION
    21. 21. EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>Performance with Dual queue </li></ul><ul><li>Unfairness of NRT Packet </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    22. 23. Observation <ul><li>Compare to our Evaluation </li></ul><ul><ul><li>packet drop rate </li></ul></ul><ul><li>50 packets for the RT queue size </li></ul><ul><li>Downlink is disadvantaged </li></ul><ul><li>Simulation results are based on 11 Mbps </li></ul>
    23. 24. EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>Performance with Dual queue </li></ul><ul><li>Unfairness of NRT Packet </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    24. 26. Observation <ul><li>Effect of queue size </li></ul>
    25. 27. EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>Performance with Dual queue </li></ul><ul><li>Unfairness of NRT Packet </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    26. 29. Observation <ul><li>worst case delay 11ms </li></ul><ul><ul><li>Queuing delay with the single queue </li></ul></ul><ul><ul><li>MAC HW queue wireless channel access </li></ul></ul><ul><li>NRT queues </li></ul><ul><ul><li>Size = 50 or 100  increase as the number of TCP flows increases </li></ul></ul><ul><ul><li>Size = 500  almost no change in delay </li></ul></ul>
    27. 30. EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>Performance with Dual queue </li></ul><ul><li>Unfairness of NRT Packet </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    28. 32. Observation <ul><li>Unfairness </li></ul><ul><ul><li>between upstream and downstream TCP flows with the queue sizes of 50 and 100 </li></ul></ul><ul><li>Queue size for the AP should be large enough - This is good for us </li></ul>
    29. 33. EVALUATION RESULT <ul><li>Pure VoIP </li></ul><ul><li>Effect of VoIP with different TCP session numbers </li></ul><ul><li>Performance with Dual queue </li></ul><ul><li>Unfairness of NRT Packet </li></ul><ul><li>Effect of MAC HW Queue </li></ul>
    30. 35. Observation <ul><li>Delay of downlink voice packets </li></ul><ul><ul><li>increases linearly proportional to the MAC HW queue size </li></ul></ul><ul><li>Another effect </li></ul><ul><ul><li>with the MAC HW queue size of 8, the worst delay is observed with a single VoIP session </li></ul></ul><ul><li>Large MAC HW queue size is still aceptable </li></ul><ul><ul><li><25ms </li></ul></ul>
    31. 36. Brief Summary <ul><li>Driver of the 802.11 MAC controller </li></ul><ul><li>Strict priority queuing </li></ul><ul><li>Bottleneck of TCP in WLAN  downlink </li></ul>
    32. 37. VoIP and 802.11e QoS standards
    33. 38. What’s the difference between Wireless/Wired VoIP? <ul><li>Mobility </li></ul><ul><ul><li>Roaming </li></ul></ul><ul><li>Security </li></ul><ul><ul><li>Hidden UA </li></ul></ul><ul><li>Quality of Service </li></ul><ul><ul><li>Guarantee of voice quality </li></ul></ul>
    34. 39. Hidden Node Problem
    35. 40. Quality of Service <ul><li>QoS problems </li></ul><ul><li>802.11e QoS standard </li></ul><ul><li>A non-standard solution – </li></ul><ul><li>Dual Queue Strategy </li></ul>
    36. 41. QoS Problems <ul><li>Dropped Packets </li></ul><ul><li>Delay </li></ul><ul><li>Jitter </li></ul><ul><li>Out-of-order Delivery </li></ul><ul><li>Error </li></ul><ul><li>VoIP requires strict limits on jitter and delay </li></ul>
    37. 42. Quality of Service <ul><li>QoS problems </li></ul><ul><li>802.11e QoS standard </li></ul><ul><li>A non-standard solution – </li></ul><ul><li>Dual Queue Strategy </li></ul>
    38. 43. IEEE 802.11e <ul><li>A draft standard of July 2005 </li></ul><ul><li>It defines a set of QoS enhancements for WLAN applications </li></ul><ul><li>and enhances the IEEE 802.11 Media Access Control (MAC) layer </li></ul>
    39. 44. Coordination Function <ul><li>For stations to decide which one has the right to deliver its packets </li></ul><ul><li>802.11: DCF & PCF </li></ul><ul><li>802.11e: EDCF & HCF </li></ul>
    40. 45. Original 802.11 MAC <ul><li>Distributed Coordination Function (DCF) </li></ul><ul><li>Point Coordination Function (PCF) </li></ul>
    41. 46. Distributed Coordination Function (DCF) <ul><li>Share the medium between multiple stations </li></ul><ul><li>Rely on CSMA/CA and optional 802.11 RTS/CTS </li></ul>
    42. 47. How DCF works?
    43. 48. DCF Limitations <ul><li>When many collisions occur, the available bandwidth will be lower </li></ul><ul><li>No notion of high or low priority traffic </li></ul><ul><li>A station may keep the medium </li></ul><ul><li>If the station has a lower bitrate, all other stations will suffer from that </li></ul><ul><li>No QoS guarantees </li></ul>
    44. 49. Original 802.11 MAC <ul><li>Distributed Coordination Function (DCF) </li></ul><ul><li>Point Coordination Function (PCF) </li></ul>
    45. 50. Point Coordination Function (PCF) <ul><li>Available only in &quot;infrastructure&quot; mode </li></ul><ul><li>Optional mode, only very few APs or Wi-Fi adapters actually implement it </li></ul><ul><li>Beacon frame, Contention Period, and Contention Free Period </li></ul>
    46. 51. How PCF works?
    47. 52. 802.11 MAC Layer Framework
    48. 53. 802.11e MAC Protocol Operation <ul><li>Enhanced DCF (EDCF) </li></ul><ul><li>Hybrid Coordination Function (HCF) </li></ul>
    49. 54. Enhanced DCF (EDCF) <ul><li>Define Traffic Classes </li></ul><ul><li>High priority traffic has a higher chance of being sent than low priority traffic </li></ul><ul><li>A &quot;best effort&quot; QoS </li></ul><ul><li>Simple to configure and implement </li></ul>
    50. 55. 802.11e MAC Protocol Operation <ul><li>Enhanced DCF (EDCF) </li></ul><ul><li>Hybrid Coordination Function (HCF) </li></ul>
    51. 56. Hybrid Coordination Function (HCF) <ul><li>Works a lot like the PCF </li></ul><ul><li>Main difference with the PCF: Define the Traffic Classes (TC) </li></ul><ul><li>Stations are given a Transmit Opportunity (TXOP) </li></ul><ul><li>The most advanced (and complex) coordination function </li></ul><ul><li>QoS can be configured with great precision </li></ul>
    52. 57. What’s the difference between Wireless/Wired VoIP? <ul><li>Quality of Service </li></ul><ul><li>Security </li></ul><ul><li>Mobility </li></ul>
    53. 58. IEEE 802.11i <ul><li>The draft standard was ratified on 24 June 2004 </li></ul><ul><li>Supersede Wired Equivalent Privacy (WEP) </li></ul><ul><li>Wi-Fi Protected Access (WPA) is a subset implementation </li></ul><ul><li>And WPA2 is the full implementation </li></ul>
    54. 59. IEEE 802.11i (cont.) <ul><li>802.1X for authentication (entailing the use of EAP and an authentication server) </li></ul><ul><li>RSN for keeping track of associations </li></ul><ul><li>AES-based CCMP to provide confidentiality, integrity and origin authentication </li></ul><ul><li>Authentication process: four-way handshake </li></ul>
    55. 60. The Four-Way Handshake
    56. 61. What’s the difference between Wireless/Wired VoIP? <ul><li>Quality of Service </li></ul><ul><li>Security </li></ul><ul><li>Mobility </li></ul>
    57. 62. IEEE 802.11f & 802.11r <ul><li>802.11f: Inter-Access Point Protocol </li></ul><ul><li>802.11r: Fast roaming </li></ul>
    58. 63. Conclusion
    59. 64. Paper References 1 <ul><li>Jeonggyun Yu, Sunghyun Choi, Jaehwan Lee, “Enhancement of VoIP over IEEE 802.11 WLAN via Dual Queue Strategy” </li></ul><ul><li>Moncef Elaoud, David Famolari, and Ahbrajit Ghosh, “Experimental VoIP Capacity Measurements for 802.11b WLANs” </li></ul><ul><li>Mustafa Ergen, “I-WLAN: Intelligent Wireless Local Area Networking” </li></ul><ul><li>Gyung-Ho Hwang, Dong-Ho Cho, “New Access Scheme for VoIP Packets in IEEE 802.11e Wireless LANs” </li></ul><ul><li>Sai Shankar N, Javier del Prado Pavon, Patrick Wienert, “Optimal packing of VoIP calls in an IEEE 802.11a/e WLAN in the presence of QoS Constraints and Channel Errors” </li></ul>
    60. 65. Paper Reference 2 <ul><li>Experimental VoIP capacity measurements for 802.11b WLANs </li></ul><ul><li>Enhancement of VolP over IEEE 802.11 WLAN via dual queue strategy </li></ul><ul><li>An experimental study of throughput for UDP and VoIP traffic in IEEE 802.11b networks </li></ul><ul><li>Admission control for VoIP traffic in IEEE 802.11 networks </li></ul><ul><li>How well can the IEEE 802.11 wireless LAN support quality of service </li></ul>
    61. 66. Web Site References <ul><li>http://www.ieee.or.com/Archive/80211/802_11e_QoS_files/frame.htm </li></ul><ul><li>http://en.wikipedia.org/wiki/IEEE_802.11 </li></ul><ul><li>http://www.cs.nthu.edu.tw/~nfhuang/chap13.htm#13.1 </li></ul><ul><li>http://www.eettaiwan.com/ART_8800360909_675327_3f3ffd7b_no.HTM </li></ul><ul><li>http://it.sohu.com/2003/12/11/09/article216750985.shtml </li></ul>

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