AIL: Actively Intelligent Link-Layer Handoff

1. AIL: Actively Intelligent Link-Layer Handoff Guo-Yuan Mikko Wang E-Mail: mikko_wang@act-tel.com.tw

2. Agenda • Introduction • Research Background • AIL • Simulation and Analysis • Discussion

3. Introduction • Operating modes specified in IEEE 802.11 MAC • Ad Hoc • Two or more MNs recognize each other and establish a peer-to-peer communication without any existing infrastructure. • Infrastructure • It uses AP to bridge all data between the MNs associated to it. • In this scheme, it is concerned with the network that sets with infrastructure mode which is widespread use in most of public places. Internet MN MN MN AP AP MN

4. Introduction • The mobility characteristic of MN will make it change the associated AP frequently. Router AP AP AP MN MN MN Move Move

5. Introduction • Mobility Protocol • Allows: • MN can migrate between different IP networks without breaking network-layer connectivity and disrupting transport sessions. • Occurs: • When a MN moves from one network-level point of attachment to another, a Mobility handoff takes place. • Before Completed: • Packets destined for the MN will not be delivered.

6. Introduction • This handoff latency may cause degradation in communication quality, specifically when real-time applications are used. • The faster the link speed, the more packets will be lost during handoff. • When the TCP is used for data transmission, roam around wireless networks may diminish the performance due to TCP retransmission policy. • In addition • Mobility handoff is just a part in whole handoff procedure. Before the Mobility handoff, the link-layer handoff will take place first.

7. Research Background • Overview of handoff relating objects Mobility Handoff Link-Layer Handoff

8. Research Background • Link-Layer Handoff • potential phase • detection of the need for the handoff • probe phase • collects the acquisition of the information necessary for the handoff • auth phase • the handoff is performed during this phase

9. Research Background AP Signal strength degrades below the threshold Failed frame transmission MN AP AP AP MN MN must scan all channels AP AP Switch to Previous associated New association MN

10. Research Background • Experiment network • Configuration: • Wired: 100Base-T • Wireless: 802.11b • Open System

11. Research Background • Duration of link-layer handoff bottleneck • Primary contributor • Fortunately, all cards can take advantage of the information provided by the physical layer to skip it completely. Without discussing the latency of Mobility Protocols,this link-layer handoff latency already made many real time applications can not meet their requirements. Shortest phase & neglected • International Telecommunication Union recommends the overall latency in VoIP not to exceed 50 ms. • An optimization scheme is needed to reduce the latency of link-layer handoff within acceptable bounds. • The whole handoff latency (i.e., includes link-layer and Mobility Protocol) can have a chance to reach the requirements of real time applications.

12. AIL • AIL: Actively Intelligent Link-Layer Handoff • A pro-active link-layer handoff scheme • Based on L2-Optimize • Overcome the physical limitation of signal receiving • Continuously monitor the signal strength of channels • Actively determine the suitable handoff opportunity • Benefit: • Since the MN can has a better signal quality with the associated AP, it has more probability to do the communication at higher transmission speed and the probability of retransmission on wireless link should become lower.

13. AIL How about the packets transmitted and received during a pro-active channels probing? Every AIL_interval, MN will do a pro-active channels probing Channel 1 Channel 6 Output: system will buffer it Input: use Power Saving Mode (PSM) AP1 AP2 Depends on the Channel_Register to send probe requests Collects and measures the probe responses Switch to New association associating probe response probe request After a pro-active channels probing, MN will switch back to its original channel then determine the opportunity of handoff MN If no responses probe request If it is AIL_Gate better than the associating AP, then handoff probe response probe request MN will cancel the pro-active channels probing to the channel for the following Postponing_Time AP4 Channel ? AP3 Channel 11

14. Simulation and Analysis • Simulation and Analysis • Configurations • NS-2 with necessary modifications • Based on L2-Optimize • IEEE 802.11b • Open system (authentication)

15. Simulation and Analysis • Signal Quality Experiment Threshold This handoff makes an obvious latency to communication, and the influence will be presented in the following experiments.

16. Simulation and Analysis • Signal Quality Experiment AIL_Gate Average signal quality: IEEE: 44.57 AIL: 58.31 It only spends CST＋the duration of auth phase

17. Simulation and Analysis • UDP Transmission Experiment CN transmits 64 bytes of UDP packets to the MN at 10 ms intervals 16 packets lost 5 packets retransmitted

18. Simulation and Analysis • UDP Transmission Experiment Buffered by AP No packet lost!

19. Simulation and Analysis • TCP Transmission Experiment MN downloads a 15 MB file from CN Average transmission rate: Static MN: 568.8 KB/s With IEEE: 549.33 KB/s With AIL: 568.6 KB/s

20. Discussion • Compatibility • Apply via driver, system service or daemon • Working with IEEE 802.11 a/b/g • Backward compatible • Flexibility • Many parameters in AIL can be changed depend on the collected information • The decision that when the actively channel switch should be executed can become more intelligent

21. Discussion • Advantages • Continuously monitor the signal qualities of all channels in its communication range • MN can operate under stronger and stable signal strength • Higher communication speed • Avoid retransmission on wireless link • Actively determine the suitable handoff opportunity • Disadvantages • MN will send ‘2× the number of potential channels’ every AIL_interval seconds

22. The EndThank youComments