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Cooperation between stations in wireless networks

Cooperation between stations in wireless networks. Andrea G. Forte, Henning Schulzrinne Department of Computer Science, Columbia University Presented by: Azbayar Demberel. Duke University April 19, 2008. Agenda. Motivation Cooperative roaming Results Conclusion.

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Cooperation between stations in wireless networks

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  1. Cooperation between stations in wireless networks Andrea G. Forte, Henning Schulzrinne Department of Computer Science, Columbia University Presented by: Azbayar Demberel Duke University April 19, 2008

  2. Agenda • Motivation • Cooperative roaming • Results • Conclusion

  3. VoIP and 802.11: terminal mobility problem AP AP Mobile Node L2 handoff: in case subnets are the same L3 handoff: in case the new AP is in different subnet Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf MotivationCooperative roaming Results Conclusion

  4. L2 handoff in 802.11 MotivationCooperative roaming Results Conclusion

  5. L3 handoff in 802.11 MotivationCooperative roaming Results Conclusion

  6. Handoffs due to mobility • L2 handoff (~100-400 ms) • Scanning (>90%) • Network authentication • Re-association • L3 handoff (~1000ms) • Subnet change discovery • IP address acquisition (>90%) • Application handoff • Informing correspondent node of new IP address MotivationCooperative roaming Results Conclusion

  7. Cooperative roaming: goals and solution • Fast handoff for real-time multimedia in any network • Different administrative domains • Various authentication mechanisms • No changes to protocol and infrastructure • Fast handoff at all the layers relevant to mobility • Link layer • Network layer • Application layer • New protocol: Cooperative Roaming • Complete solution to mobility for real-time traffic in wireles networks • Working implementation available MotivationCooperative roaming Results Conclusion

  8. Cooperative roaming: overview • Stations can cooperate and share information about the network (topology, services) • Stations can cooperate and help each other in common tasks such as IP address acquisition • Stations can help each other during the authentication process without sharing sensitive information, maintaining privacy and security • Stations can also cooperate for application layer mobility and load balancing MotivationCooperative roaming Results Conclusion

  9. Signal Low Selective Scanning Store AP Info to Cache 6 6 1 11 11 1 1 B B C C A A A Cache Cache Key Best Key Best Next Next A B A C B 6 11 Cooperative Roaming: AP caching SSID, Channel, SubnetID (e.g. MAC(A), 1, 160.39.5.0) Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt MotivationCooperative roaming Results Conclusion

  10. Cooperative Roaming: AP caching Signal Low Selective Scanning Store AP Info to Cache 6 6 1 11 11 1 1 B B C C A A A Cache Cache Key Best Key Best Next Next A B C B A C B B C A C A Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt MotivationCooperative roaming Results Conclusion

  11. L2 cooperation protocol Mobile node B Mobile node A Mobile node C 1. InfoReq (cache A) 1. InfoReq (cache A) Random backoff 2. InfoResp diff(cache A, cache B) 2. InfoResp diff(cache A, cache C) MotivationCooperative roaming Results Conclusion

  12. L3 cooperation protocol Mobile node B (subnet 1) Mobile node A (subnet 2) Mobile node C (subnet 2) 1. AmnDiscover (subnet 1) 1. AmnDiscover (subnet 1) Acquire IP, using MAC(A) from DHCP server Subnet1: nodeB( Mac(B), IP(B)) 2. AmnResp (MAC(B), IP(B)) 3. IpReq (MAC(A)) Cache: subnet1( IP(A), IP(router)) 4. IpResp (MAC(A), IP(A), IP(router)) L2 handoff begins MotivationCooperative roaming Results Conclusion

  13. Cooperation in the authentication itself not possible  keys, certificates (sensitive info) Use relay node (RN) to relay packets during authentication No bridging delay Use timeout to achieve fairness What about RN mobility? Cooperative authentication MotivationCooperative roaming Results Conclusion

  14. Experiment environment • 2 subnets/AP’s • 4 nodes (1 roamer, 1 helper, 2 sniffers) • Roamer moved between two AP’s: perform L2, L3 handoff …i.e. extremely simple! MotivationCooperative roaming Results Conclusion

  15. Experiment results MotivationCooperative roaming Results Conclusion

  16. Cooperative roaming vs. 802.11 Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf MotivationCooperative roaming Results Conclusion

  17. Cooperative roaming vs. 802.11 Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf MotivationCooperative roaming Results Conclusion

  18. Discussion • Too simple experiment: congestion and backoff might diminish all the benefits, in real life • Assumes spatial locality / node “knows” what the next AP will be. • No info on memory management policies: how often to ask neighbors • In many places uses magic wand approaches (e.g. detect subnet change) • CR might benefit from location routing • Application layer mobility, load balancing left out MotivationCooperative roaming Results Conclusion

  19. Summary • Seamless/near-seamless handoff • Requires cooperation of many other nodes to achieve the benefits • Worst case scenario ~ current 802.11 • Room for improvement: mobility detection, application layer handoff … MotivationCooperative roaming Results Conclusion

  20. Thank you Questions? Comments?

  21. Backup slides From: http://www.cs.umd.edu/~waa/pubs/handoff-lat-acm.pdf

  22. Subnet Discovery (1/2) • Current solutions • Router advertisements • Usually with a frequency on the order of several minutes. • DNA working group (IETF) • Detecting network attachments in IPv6 networks only. No solution in IPv4 networks for detecting a subnet change in a timely manner.

  23. Subnet Discovery (2/2) • Proposed approach • Send bogus DHCP_REQUEST (using loopback address). • DHCP server responds with a DHCP_NAK • From the NAK extract subnet information such as default router IP address. • The client saves the default router IP address in cache. • If old AP and new AP have different default router, the subnet has changed.

  24. Application layer handoff • MN builds a list of {RNs, IP addresses}, one per each possible next subnet/AP • RFC 3388 • Send same media stream to multiple clients • All clients have to support the same codec • Update multimedia session • Before L2 handoff • Media stream is sent to all RNs in the list and to MN (at the same time) using a re-INVITE with SDP as in RFC 3388 • RNs do not play such streams • After L2 handoff • Tell CN which RN to use, if any (re-INVITE) • After successful L2 authentication tell CN to send directly without any RN (re-INVITE) • No buffering necessary • Handoff time: 15ms (open), 21ms (802.11i) • Packet loss negligible

  25. Experimental Results (1/2) Router CN MN DHCPd L2 handoffcomplete DHCP Req. Detecting subnet change 22 ms NAK ARP Req. 138 ms Waiting time IP acquisition ARP Req. 4 ms ARP Resp. Processing overhead 4 ms SIP INVITE 29 ms SIP signaling SIP OK RTP packets (TEMP_IP) SIP ACK

  26. Handoff Scenarios • Scenario 1 • The MN enters in a new subnet for the first time ever. • Scenario 2 • The MN enters in a new subnet it has been before and it has an expired lease for that subnet. • Scenario 3 • The MN enters in a new subnet it has been before and still has a valid lease for that subnet.

  27. IP Selection (1/3) • Scenario 1 • Select random IP address starting from the router’s IP address (first in the pool). MN sends 10 ARP requests in parallel starting from the random IP selected before. • Scenario 2 • Same than scenario 1 except that we start to send ARP requests to 10 IP addresses in parallel, starting from the IP we last used in that subnet. • Scenario 3 • We do not need TEMP_IP as we have a valid lease. We just renew the lease.

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