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Use of WLAN in Mobile Ad hoc Networks

Use of WLAN in Mobile Ad hoc Networks. Jan Bording Mail: jan.bording@applica.no Phone: +47 38 25 87 51. Erlend Knutsen Mail: erlend.knutsen@no.thalesgroup.com Phone: +47 22 63 88 41. Thales Communications AS & Applica AS. More than 20 years experience on:

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Use of WLAN in Mobile Ad hoc Networks

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  1. Use of WLAN in Mobile Ad hoc Networks Jan BordingMail: jan.bording@applica.noPhone: +47 38 25 87 51 Erlend KnutsenMail: erlend.knutsen@no.thalesgroup.comPhone: +47 22 63 88 41

  2. Thales Communications AS & Applica AS • More than 20 years experience on: • Specification and implementation of secure distributed and mobile telecommunication systems • Targeting user groups with special requirements and high demands • Main areas relevant for Project MESA: • Communications Security • Robust and distributed networking (routing in packet radio networks) • Quality of Service in IP networks • Low-bandwidth mobile networks • National and International Standardization groups and research projects For more information: http://www.thales.no/ http://www.applica.no/

  3. Possible contributions to MESA • Specification of communications reference architectures • Testing of state of the art communications technology • Implementation and demonstration of prototypes • Local experience from applied prototyping • Reviewing contributions from other participants

  4. Hospital Rescue coordination centre A rescue scenario

  5. MANET – Mobile Ad hoc NETworks B C A D - Mobility - Self configuring and healing - Rapid Deployment - High capacity - Independent of public infrastructure - Relaying

  6. A layered approach: Network Layer (IP) LLC(IEEE 802.2) Link Layer (LLC sublayer) Link Layer (MAC sublayer) WLAN(IEEE 802.11) Physical Layer (Radio modem)

  7. The basic WLAN configurations: Independent BSS (IBSS) (ad hoc) Infrastructure BSS AccessPoint

  8. Use of WLAN in mobile ad hoc networks: Independent BSS (IBSS) (ad hoc) with relays

  9. Sender Receiver Relay Relay Relay WLAN Test Results Throughput (Mb/s) 1,5 1,5 1,0 0,8 0,5 0,5 0,4 Relays 0 1 2 3 Throughput measurements

  10. Sender Receiver Relay Relay Relay WLAN Test Results Delay (ms) 12 11,8 9 8,8 6,0 6 3 2,9 Relays 0 1 2 3 Delay measurements

  11. WLAN Test Observations Routing traffic is lost at high traffic load: Message Sender Receiver Normal, unicast traffic: N resendings if ackis lost. Ack Message Sender Receiver No resending, asack is not used. Broadcast traffic(e.g. Routing): As routing is broadcasting, and broadcasting has no ack in WLAN, the first messages to be lost at high traffic, are the routing messages. This leads to short network break-downs. We need priority for routing traffic, i.e. QoS.

  12. WLAN Test Observations Routing sets up poor routes: Routing Sender Receiver Routing sets up aroute directly to receiver Traffic Relay Fading means that sometimes the link from sender to receiver is good enough to get routing messages directly through. Routing will then set up a direct route from sender to receiver.Fading may then cause that the receiver can not be reached directly afterall, and the traffic is lost. This may cause flip-flops in the routing.

  13. Voice over IP Reasonable short delay • Duplex voice is possible, but demands extremely low channel efficiency. • Simplex voice can handle longer delays and is more practical. Low channel efficiency Long headers Short packets Contention time ~100 byte header Payload High traffic Necessary with retransmissions High collision rate Long delay Multiple hops Conclusion

  14. Voice over IP - Best-Case Channel efficiency Calculated channel efficiency with one hop only:

  15. Voice over IP - Best-Case Number Of Channels Number of channels for different coding algorithms:

  16. WLAN problems • WLAN PROBLEMS: • Dramatic reduction in throughput when 1 and 2 relays are added. • Relaying causes major increase in delays. • WLAN has no acknowledgement for broadcast traffic. Routing uses broadcast. This leads to that at high traffic the routing traffic looses and the network breaks down. I.e. we need priority and QoS. • Fading problems may lead to that unstable routes are set up. • Inefficient for real-time traffic using small packets. • Security regarding denial of service attacks and also confidentiality is not good enough in commercial WLAN standards.

  17. New WLAN-standards New WLAN standards will solve some of the WLAN problems: 802.11a Higher bandwidth:54 Mbps in 5 GHz 802.11g Higher bandwidth:54 Mbps in 2.4GHz 802.11e Introduces QoS 802.11i Improves Security

  18. WLAN conclusions • CONCLUSIONS: • WLAN may as a short-term solution be used in rescue scenarios when new standards for QoS, security and higher speed is used. • In a long-term solution we need a dedicated spectrum for rescue scenarios (can possible be combined with military usage).

  19. Further work FURTHER WORK: • Further evaluate the requirements for rescue operations. • Experimenting with new WLAN standards. • Sorting out the QoS questions. • Sorting out the security questions. • IP addressing and name handling for nodes. • Group handling. • Try to find solutions that can be used in a rescue operation for the near future. • Make a demonstrator for use of ad hoc technology in a rescue operation.

  20. Thank you ! Erlend KnutsenMail: erlend.knutsen@no.thalesgroup.comPhone: +47 22 63 88 41 Jan BordingMail: jan.bording@applica.noPhone: +47 38 25 87 51

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