1. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 1 Efficient Routing through Late Binding in Wireless Meshes Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2005-09-20 Authors:

2. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 2 Abstract Traditional routing in wired and wireless networks, including mesh networks, typically choose a deterministic path on which packets are routed. Path changes occur over a relatively longer time scale with detection of changes in network path properties. However, many characteristics of the wireless environment change at much smaller timescales than what routing protocols can react to. In this work, we contend that traditional routing approaches, when applied to wireless mesh networks miss significant opportunities of the wireless broadcast or multicast advantage in route selection. In our proposed work, we define a new mechanism for routing in wireless mesh networks, where the exact path choice is instantiated only at packet transmission time, taking into account exact channel characteristics. Our analysis shows that such an approach can lead to significant performance improvements in many multi- hop wireless networking scenarios, and particularly in wireless mesh networks.

3. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 3 Overview and Assumptions A multi-hop and multi-radio wireless mesh network –Mesh Nodes and Stations Problems explicitly addressed in this talk: –Routing metric and its implications –Routing strategy and its implications –Transmission power control (to a limited extent) Problems not explicitly addressed (but we have interesting solutions for): –Channel assignment

4. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 4 Objective High throughput routing –Maximize amount of traffic from STAs to Mesh Access Points (MAPs) Tx power control not necessary for energy efficiency –Because mesh nodes are usually powered Tx power control necessary to reduce contention –And thus achieve high throughput –Choice of Tx power depends on link characteristics

5. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 5 Talk Outline Routing with late binding Cost metrics Load balancing Summary and future work

6. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 6 Well-defined path derived from routing protocol Cost (ETX) = 4 (if no failures on path) Traditional routing Other links ignored at packet forwarding time S 3 12D 6 45

7. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 7 Well-defined path derived from routing protocol Cost (ETX) = 10 (given a sequence of failures) Traditional routing Packet loss S 3 12D 6 45

8. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 8 Problem with traditional routing A single deterministic apriori path No “wireless multicast/broadcast advantage”

9. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 9 Routing with late binding Exploit diversity in wireless environments Bind exact paths after packet transmission in each hop –No pre-determined single path Exploits “wireless multicast/broadcast advantage” Gain greater cost efficiency Works with all reasonable metrics (not just hop count)

10. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 10 Routing with late binding 3 D 6 Packet loss S12 45 Transmit each packet towards intended next hop (intended next hop decided as before)

11. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 11 Routing with late binding 3 D 6 S12 45 Packet loss Transmit each packet towards intended next hop (intended next hop decided as before)

12. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 12 Routing with late binding S 3 D 6 12 45 Packet loss

13. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 13 Routing with late binding S1 4 3 D 6 2 5 Cost (Num. Tx) = 4 (Compare to Cost = 10 for a deterministic path)

14. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 14 Routing with late binding S1 4 3 D 6 2 5 Cost (Num. Tx) = 4 (Compare to Cost = 10 for a deterministic path) Number of path choices = 2 * 2 * 2 = 8 We just need one good path!

15. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 15 Routing with late binding S1 4 3 D 6 2 5 Need additional mechanism to deal with redundancy What if both (or three paths) deliver the same packet? Interference Need simple protection mechanisms

16. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 16 Routing with late binding 3 D 6 S12 45 Protection against redundancy RTS

17. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 17 Routing with late binding 3 D 6 S12 45 Protection against redundancy CTS

18. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 18 Routing with late binding 3 D 6 S12 45 Protection against redundancy Data

19. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 19 Routing with late binding 3 D 6 S12 45 RTF: Request to Forward (more than an ACK) RTF 4 on receiving 1’s RTF suppresses its own RTF

20. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 20 Routing with late binding 3 D 6 S12 45 RTF Staggered in time probabilistically, based on cost (Cost(1,D) < Cost(4,D) and so 1 sends first) Each potential forwarder that did not hear another RTF, sends an RTF (If 4 did not hear 1’s RTF)

21. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 21 Routing with late binding 3 D 6 S12 45 CTF: Confirm to Forward CTF(1) S confirms forwarding role for only one of them

22. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 22 Routing with late binding 3 D 6 S12 45 RTS Repeats at next hop and so on … RTF send by nodes that improve cost to destination (4 will not send RTF to 1)

23. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 23 Talk Outline Routing with late binding Cost metrics Load balancing Summary and future work

24. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 24 Towards a routing metric Consider the single-channel case If packet loss rate = p, then expected number of transmissions is 1 / (1-p) [under independence assumption] If packet size = s and Tx data rate = B, then channel occupancy duration is s / B Transmit power translates to range of interference –We also consider the number of interfered nodes due to the transmission

25. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 25 S 3 12D 6 45 A proposed metric Loss rate = p Intefered node count = n Tx data rate = B Packet size = s Cost = (n * s) / [B (1-p)] Loss rate = 0.5, Tx data rate = 1 Mbps Interfered nodes = 4, Packet size = 1 Kb Cost = 0.008

26. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 26 Metric for multi-channel case Need to account for interference effects due to channel assignment Possible to design good metrics (left out of scope here)

27. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 27 SD Link Loss Rate = 0% Cost ~ 4 * 4 = 16 (Tx range = 1) Transmit power control Data rate: 1 Mbps Packet size: 1 Kb

28. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 28 SD Link Loss Rate = 0% Cost ~ 8 * 4 = 32 (Tx range = 1.5) Transmit power control

29. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 29 SD Link Loss Rate = 0% Cost ~ 12 * 2 = 24 (Tx range = 2) Transmit power control

30. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 30 Transmit power control When loss rate = 0%, optimal tx range = 1 i.e., guarantee minimal connectivity of topology Changes with loss rate in channels

31. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 31 S D Link Loss Rate = 50% Cost ~ 8 * 2 = 16 (Tx range = 1) Transmit power control Data rate: 1 Mbps Packet size: 1 Kb Traditional deterministic routing

32. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 32 S D Link Loss Rate = 50% Cost ~ 16 * 1 = 16 (Tx range = 1.5) Transmit power control Traditional deterministic routing

33. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 33 Transmit power control For 50% loss on channels and given example: –Traditional deterministic routing: Tx = 1 is same as Tx = 1.5 –Proposed routing with late binding: Tx 1.5 is better than Tx = 1 –Also Tx = 1 (late binding) is better than Tx = 1.5 (traditional) Bottomline: Tx power control had to re-considered for routing with late binding –Details offline

34. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 34 Load balancing May have multiple alternate mesh gateway nodes Typically STAs can choose any such gateway Choice should be governed by traffic loads on paths Defined an updated cost metric to reflect this

35. ppt.: IEEE 802.11-05/0909r0 Submission September 2005 Suman Banerjee, UW-MadisonSlide 35 Summary of work Routing with late binding is beneficial Re-visited two problems –Tx power control –Channel assignment (for multi-channel wireless meshes) Results indicate that proposed mechanisms are efficient Implementation on our wireless mesh testbed –Publicly available soon (please send email if interested) Proposed mechanisms have wider applicability (as our other results show) –Energy efficient reliable routing in wireless sensor networks –Efficient geographic routing –etc. Questions and comments: suman@cs.wisc.edu