1. An Efficient Implementation of File Sharing Systems on the Basis of WiMAX and Wi-Fi Jingyuan Li, Liusheng Huang, Weijia Jia, Mingjun Xiao and Peng Du Joint Advanced Research Institute of City University of Hong Kong and University of Sci. Tech. China Suzhou, China 報告 : 羅世豪

2. Outline 一. Introduction  WiMAX Overview and Mesh Mode 三. Overview of Our File Sharing System  File Publication  File Lookup  File Transportation 七. Analysis  Simulations  Conclusion

3. Introduction (1/1)  Both P2P file sharing systems and the WMAN standard WiMAX have a brilliant future. Therefore, combining the two techniques surely will bring the benefits to the users of both sides.  The problem is: “do the facilities of WiMAX efficiently support the structures of file sharing systems?”.  The conflict of inefficiency in pure P2P file sharing systems, lack of air interfaces and energy resources are the most severe problems that fundamentally retard the growth of P2P file sharing systems on wireless networks.  In this paper, we propose a layered P2P file sharing structure on WiMAX and Wi-Fi network infrastructures.

4. WiMAX Overview and Mesh Mode (1/4)

5. WiMAX Overview and Mesh Mode (2/4)  In WiMAX MAC layer standard, there are two different network architectures:  The point-to-multipoint (PMP) mode  The mesh mode.  The main difference between the PMP and optional mesh mode is that,  In the PMP mode, traffic only occurs between the base stations (BS) and subscriber stations (SS)  In the mesh mode, traffic can be routed through other SSs and can occur directly between SSs.

6. WiMAX Overview and Mesh Mode (3/4) SS

7. WiMAX Overview and Mesh Mode (4/4)  The architecture is an ad-hoc like structure in which SSs act as the routers.  Traffic is routed through other SSs or occurs directly among the SSs. It should be noted that, there is no need for the SSs to connect directly to the BS.  We suppose that Wi-Fi technology is used to connect end hosts to the corresponding SS and the backhaul of the network is wired.

8. Overview of Our File Sharing System (1/2)

9. Overview of Our File Sharing System (2/2)  End devices under the same SS are connected with Wi-Fi technology.  Every two end hosts are one-hop connected and each end host in the same local area network is connected directly to the SS.  We propose a changed dynamic source routing (CDSR) lookup protocol on SSs mesh networks where the number of SSs under a BS is not large enough to efficiently construct a DHT based file sharing architecture.  By implementing CDSR on SSs mesh networks, our layered file sharing system can support keyword lookup within a SSs mesh network.  We also design DHT based file lookup architecture on BSs networks, because BSs networks are cable connected and able to tolerate the extra traffic loads.

10. File Publication (1/2)  When an end host s releases a file f to the file sharing system, it registers its information in two places:  The SS the end host is directed connected to.  A BS in the BS network.

11. File Publication (2/2)  Firstly, s releases the file name and a bunch of keywords to the SS to which it is registered.  Guarantee that our system support content lookup within the same range of a BS.  Secondly, s computes the hash value of the file name h(f) and registers the file to the corresponding BS in the BS network, where h(f)=h(BS i ).  BS i is the ID of the corresponding BS.  If such BS i does not exist, then the information is stored in the nearest next BS as that is implemented in the Chord system.  Registering f to the DHT based BS overlay network enables the end hosts from other BSs to share their resources together in a robust and efficient way.

12. File Lookup (1/6)

13. File Lookup (2/6)  When an end host d requests a file f, it may require three performance steps to finally find the requested resource.  Firstly, d searches f on end hosts within the SS it is registered.  Because all of the end devices are one-hop connected, d instantly knows whether f exits or not.  If f does not exist within the local area network under the registering SS, then d searches the publication information within the range of the corresponding BS, i.e., the nearest SSs mesh network.  Here a changed dynamic source routing protocol (CDSR) is used to efficiently manipulate the routing problems in the SSs network

14. File Lookup (3/6)  If there is no f found in the local SSs mesh network, then the resource lookup procedure sends a request message to the DHT ring of the BSs network as Chord does, seeking fortune from hosts under other BSs.  By importing the above three layer lookup procedure, our layered P2P file sharing system guarantees the following two advantages.  The requesting end host gets the requested file as ‘near’ as possible. This saves a great amount of bandwidth for the underground wireless infrastructures.  Our system supports keywords lookup within the SSs mesh networks. On the basis of our simulations, this may be the major position that the requested file f is found.

15. File Lookup (4/6)

16. File Lookup (5/6)  CDSR is very similar to DSR algorithm in mobile ad-hoc networks except that most of the SSs are immobile as compared to the end devices in the ad-hoc networks.  The requesting end host d launches a request procedure in the SS to which it is registered in order to find f  The SS sends a request message containing the name of the file f and/or some keywords to all its neighbors in the SSs mesh network.  The neighbor SSs perform the same action until a SS finds the file f in its resource register table, or all the SSs under the range of the same BS receive the message and no match is found.  If f is found, then the source SS unicasts backwards to the requesting end host where the requesting end host saves the routing information in its routing table.

17. File Lookup (6/6)

18. File Transportation(1/1)  Resource transportation is almost the same as that of other cabled networks.

19. Analysis (1/4)  α end devices under each SS.  β SSs under each BS.  γ BSs of the whole system.  Let η be the probability of file f on each end host.  The probability P EH that a requesting end device obtains the requested file f under the same SS is shown in expression.  P EH = 1− (1−η ) α

20. Analysis (2/4)  Defining P SS as the probability of the requesting end host obtaining the requested file f under the same BS or in the nearest SSs mesh network (but not in its own Wi-Fi based local area network). P SS is shown in expression.  P SS = (1−η ) α ×[1− (1−η ) α (β −1) ]

21. Analysis (3/4)  P BS is the probability indicating that the nearest SSs mesh network does not have the file transmission request is shown in expression.  P BS = 1− (1−η ) αβ

22. Analysis(4/4)  As the popularity of resource goes higher, there is more opportunity that the requesting end host obtains the requested file within the range of the SS to which it is registered and the nearest SSs mesh network.  Enhances the performance of our layered P2P file sharing system,  Reducing both the number of lookup messages in file lookup procedure and the bandwidth requirement in WiMAX and Wi-Fi based wireless network architectures in file transportation procedure.

23. Simulations(1/6)  We simulated under an independent WiMAX wireless metropolitan area network with 100 BSs connected by cables.  Each BS controlled 25 SSs, all of which were interconnected to form a wireless SSs mesh network.  The network under each SS was set to be Wi-Fi based local area network.  End hosts under the same SS were one-hop connected and were directly connected to the SS they were registered to.  Four end hosts were registered to each SS.  The popularity of a file f was from 0.5% to 6%.

24. Simulations(2/6)

25. Simulations(3/6)  Fig. 9 describes the percentage of three types of positions of the requested file f:  Source end host which was under the same SS (Wi-Fi based local area network) with the destination end host.  Source end host which was under the same BS (SSs mesh network).  Source end host which was under other BS (BSs Chord ring).

26. Simulations(4/6)  When a file f is popular, a great number of end hosts cached it to their own memory.  Therefore the requesting end host is more likely to obtain f around its neighbors in our hierarchical system which saves a great amount of precious wireless bandwidth.  We also notice that even though a file is very unpopular (for example, only 0.5% end hosts have the file), there is still a great probability that the requesting end host gains the file within the SSs mesh network where it is located (45% in the above simulation result), as long as there are enough end hosts under the corresponding BS.

27. Simulations(5/6)  Fig. 10 presents the relationship between the number of lookup messages in the physical networks and the popularity of the requested file in our hierarchical system.

28. Simulations(6/6)  The number of lookup messages are greatly reduced as the file becomes more and more popular.  In original Chord system, the popularity of the requested file does not affect the complexity of the lookup procedure.  Our system successfully improves this inefficiency.

29. Conclusion(1/1)  We have proposed a layered P2P file sharing system on the important WiMAX and Wi-Fi wireless techniques.  By statistical analysis and practical simulations, we have shown that our layered P2P file sharing system can  Greatly reduces the number of lookup messages in physical networks.  Prevents over expenses of precious bandwidth in wireless metropolitan area networks.