1. 69821042 葉志宏 69821061 馮至芬 69821066 謝耀文 International Conference on Advanced Information Networking and Applications © 2008 IEEE DOI 10.1109/WAINA.2008.254 Kazuo Takahata.1, Shinya Takada.1, Yoshitaka Shibata.2 1.Saitama Institute Technology, 2.Iwate Prefectural University, Japan

2. 1.Abstract 2.Introduction 3.System Configuration 4.Path Selection Method 5.Prototype and Evaluation 6.Conclusions

3. So far we have developed a disaster information network which is very effective and robust using wireless network. A mobile network for disaster communication network by combination of different wireless LANs and mobile network. Currently available wireless LANs such as IEEE802.11b,g,j,n, IEEE802.16 (WiMAX), cellular network are combined with a mobile router and loaded on a car to build a mobile network node. A communication path between nodes has multiple linkls and the suitable linkl among them is selected based on the distance, power and transmission frequency. By multi-hopping those nodes, user can communicate with other user and send/receive disaster information even though some of information infrastructure are damaged. We designed and implemented a wireless mobile network with currently available different wireless network and constructed a prototyped system to evaluate the functional and performance.

4. As recent advent of wireless communication network technology, various types of wireless networks have been emerged and used in various application fields, such as hot spot at public areas, Intelligent Trafiic System, disaster communication network, etc. Since connectivity among the whole network depends on distance between the wireless network nodes, power density, transmission frequency and their cover area, network transmission speed, communication may or may not be disconnected depending on the communication environment, also mobile environment was not considered in the previous networks. By combining different standard Wireless LANs and dynamically changing the communication link and route according to the application, media to be transmitted, communication distance, network connectivity could be preserved.

5. The proposed system is shown in Fig. 1 and configured by mobile nodes loaded on a vehicle and fixed nodes. The mobile node is consisted of different standard wireless LANs and their antennas, a Router PC, a note PC and a video camera. Each node is linked one another and organizes an adhoc network and finally connected to the fixed node which is a gateway to Internet or other wide area network. Each link from one node to another has multiple channels by different wireless LANs.

6. The monitor module monitors the change of throughput and registers the current link of LANs, path and traffic load on the node to the Route list. The Route decision module determines the route of LAN based on Route list and Policy list. The connection management module observes various parameters including throughput, delay, power density, packet loss rate by periodically sending sensing packet to the neighbor nodes. The sender/receiver module sends and receives packet stream information and control information. Policy list manages poly list for router PC set by user through browser GUI.

7. Three different data including: The control data is transmitted between the connection management modules or route lists and used to determine the suitable route and link. The connection acknowledgement module is used to know and confirm the connection status to the neighbor mobile nodes by sending sensing packet. The media data is used to transmit the various users’ media data including Web., VoIP, video streaming and etc..

8. There are two types of path selection method including link section method between neighbor nodes and route selection method for route between the source node and destination node.

9. The proper link is changed among the several possible links depending on the connection status. When current connection status is worse by decreasing the power density, throughput, packet succeeding rate, then another link of LANs are selected and changed. The link selection is realized on Router PC on mobile node. The router PC periodically observes throughput, delay time, power density, throughput, packet loss rate and understands whether those links are possibly available or not on each link. The policy to use the link is also set through the GUI in advance.

10. 1. Each node grasps the end-to-end route status by periodically flooding sensing packets. 2. Router PC1 detects that the state parameter, such as throughput at the Link 1 between Router PC1 and PC2 decreased. 3. Router PC1 sends link Reconnect Request message to Router PC2 based on Policy list. 4. Router PC2 makes a tunnel for Link 2 and sends a Ready to Accept message to Route PC1. 5. Router PC1 makes a tunnel for Link 2 and sends a Ready to Reconnect message to Router PC2. 6. Communication between Router PC1 and PC2 starts and both tunnels are released. 7. The current link state is recorded.

11. The status information of currently connecting Router PCs including the Router PC number, IP address and link state is always recognized on each Router PC. When some Router PC, Router PC 2 in Fig.5 have to be exchanged from PC3 to other due to degradation of throughput.

12. The PC Router selection method is carried out in the followings steps similar to the link selection algorithm: 1. Each node grasps the end-to-end route status by periodically flooding sensing packets. 2. Router PC2 finds that the throughput between Router PC2 and PC3 decreased. 3. Router PC2 determines Router PC4 as a next route. 4. Router PC2 send a connection request to Route PC4 to change a link to another channel. 5. Router PC4 creates a tunnel for path and send reconnect ready to Router PC2. 6. Router PC2 creates a tunnel to router PC4 and eliminates the path to route PC3. 7. The current path is registered to route list in both.

13. When the current link state between the nodes gets worse, a new link connection is established. There are several parameters to be observed during communication including standard, power density, frequency of LANs, throughput, delay, packet loss, distance between the neighbor nodes. Distance between the nodes can be calculated using GPS at each node. The priority method how the current connection is changed to a new link and predefined as Policy list as follows: 1. User selected default values 2. Throughput between nodes 3. Power density of LAN 4. Packet Loss 5. Standard LAN By predefining the threshold of changing link, the communication can continue without disconnection between nodes.

14. In the Route list, two routing tables are created. One table includes default route information with normal connection nodes and their IP addresses and their priority numbers. The other table includes alternative routing information with possible connection nodes and their IP addresses.

15. The four different wireless LANs including IEEE802.11a(4.9 GHz, 10mW, 54Mbps), IEEE802.11b,g (2.4GHz,10mW, 11Mbps & 54Mbps), D-Star(1.2GHz, 1W,128Kbps) and CDMA 1X EV-DO(0.8GHz, 400mW,1.2Mbps) are installed. The function modules using C++ on mobile router PC (Mobile Pentium 3) running on 4.3 BSD Unix.

16. The thresh hold for Policy list to change the communication link is determined. Next we implemented video stream application module between the nodes. As video streaming, Midfield was applied by controlling its video quality from 56Kbps to 20Mbps using its transcoding function. When the distance between the mobile nodes are short (1~ 250m), the video stream with 5 Mbps was transmitted using default LAN by IEEE802.11g. As the distance increases, the throughput decreased under 5 Mbps when the distance was more than 250m. Then Router PC changed the wireless LAN from IEEE802.11g to IEEE802.11b with 1.5Mbps. When the distance is about 1,000m, the Rout PC changed to CDMA2000 1X EV- DO with about 200Kbps.Thus, depending on the distance, the throughput reduces dynamically and the LAN changed to transmit the video steam by changing video quality.

17. It designed and implemented a wireless mobile network with currently available different wireless networks and constructed a prototyped system to evaluate the functional and performance. Currently we are implementing dynamic routing method among adhoc network to provide end-to-end path. In the future work, the parameter values and threshold for routing method and policy rule should be optimized.