The Case for a Multi-hop Wireless Local Area Network INFOCOM 2004 Seungjoon Lee Bobby Bhattacharjee University of Maryland

2 Outline Introduction Introduction Measurement-Based Evaluation Measurement-Based Evaluation Multi-Hop WLAN Architecture and Deployment Multi-Hop WLAN Architecture and Deployment Simulation Studies Simulation Studies Conclusions Conclusions

3 Introduction The multi-hop architecture

4 Multi-Hop Wireless LAN and its advantages Multi-Hop Wireless LAN and its advantages Enhanced performance Enhanced performance Extended wireless coverage Extended wireless coverage Enabling automated re-organization of AP distribution Enabling automated re-organization of AP distribution Pitfalls Pitfalls Increased channel contention Increased channel contention Resource consumption at proxies Resource consumption at proxies Backward compatibility Backward compatibility unaware-AP, unaware-client unaware-AP, unaware-client unaware-AP, aware-client unaware-AP, aware-client aware-AP, unaware-client aware-AP, unaware-client aware-AP, aware-client aware-AP, aware-client Access Point UnawareAware Client Unaware Aware WDS MAT WDS + RAP/CAP MAT + RAP Introduction

5 Measurement-Based Evaluation Experimental Setup

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7 Multi-Hop WLAN Architecture and Deployment

8 Determine the bandwidth of a wireless path Determine the bandwidth of a wireless path Noise on the wireless channel Noise on the wireless channel Contention with other clients Contention with other clients Heuristic to compute these metrics through passive observations Heuristic to compute these metrics through passive observations Requires no active measurement traffic Requires no active measurement traffic Does not increase the contention of the data channel Does not increase the contention of the data channel An endpoint of a wireless link or any external entity with the capability to snoop packets An endpoint of a wireless link or any external entity with the capability to snoop packets

9 Multi-Hop WLAN Architecture and Deployment Clients outside direct range of AP AP Y X b x = 2 2. ForwardProxyBid / ForwardProxyRevoke 1. ForwardProxyAccept aware b w,ap = 2

10 Multi-Hop WLAN Architecture and Deployment Access Point UnawareAware Client Unaware Aware WDS MAT WDS + RAP/CAP MAT + RAP WDS : Wireless Distribution System RAP : Relaxation assisted-by AP CAP : Composition assisted-by AP MAT : MAC-level Address Translation X unaware AP Y proxy ( Emulates AP ) WDS BSS unaware

11 Multi-Hop WLAN Architecture and Deployment Access Point UnawareAware Client Unaware Aware WDS MAT WDS + RAP/CAP MAT + RAP WDS : Wireless Distribution System RAP : Relaxation assisted-by AP CAP : Composition assisted-by AP MAT : MAC-level Address Translation AP Y X 1 RTS CTS. NULL ACK 2. ForwardProxyRevoke proxy unaware aware

12 Multi-Hop WLAN Architecture and Deployment Access Point UnawareAware Client Unaware Aware WDS MAT WDS + RAP/CAP MAT + RAP WDS : Wireless Distribution System RAP : Relaxation assisted-by AP CAP : Composition assisted-by AP MAT : MAC-level Address Translation AP Y X 1. ClientDissociateRequest aware Unaware proxy 2. dissociate 3. data

13 Access Point UnawareAware Client Unaware Aware WDS MAT WDS + RAP/CAP MAT + RAP Multi-Hop WLAN Architecture and Deployment { min( b x,z, b z ) – b x } > b threshold min (5.5, 11) – 2 = 3.5 b w = min{ b w, AP} AP Y Z X W b y = 2 b x = 2 b w = 2 b z = 5.5 b w,ap = 2 b x,z = 11 BW = 11 BW = 2 ZX ForwardProxyBid ForwardProxyAccept

14 Multi-Hop WLAN Architecture and Deployment Discussion Discussion Association Overhead Association Overhead Long-term solution to provide wireless connectivity in a popular user location is to add more APs Long-term solution to provide wireless connectivity in a popular user location is to add more APs Path Oscillation Path Oscillation Reasonably large value for b threshold Reasonably large value for b threshold Upper bound on the path changing rate Upper bound on the path changing rate

15 Simulation Studies Simulated Environment Simulated Environment ns-2 ns-2 ftp traffic ftp traffic Rate Fallback Rate Fallback

16 Simulation Studies single sender C south proxy west proxy

17 Simulation Studies single sender C

18 Simulation Studies two senders B & C

19 Simulation Studies two senders B & C

20 Conclusions Defined a multi-hop WLAN architecture and quantified its benefits Defined a multi-hop WLAN architecture and quantified its benefits Define deployment paths for these multi-hop extensions that can interoperate with existing deployed WLANs Define deployment paths for these multi-hop extensions that can interoperate with existing deployed WLANs Implementing our proposed mechanisms in a prototype system Implementing our proposed mechanisms in a prototype system