Research Plan : A N ovel A pproach for T olerating Access-Point Failures

1. Research Plan : A Novel Approach for Tolerating Access-Point Failures Reporter：Mark Yang 93.05.25

2. Outline • Abstract • Related Work • Introduction • Implementation • Conclusion • Future Work 2 / 15

3. Abstract • A novel approach for tolerating Access-Point Failures. 13:00～14:00 限時搶購．全面6折 3 / 15

4. Related Work - Tolerating AP Failures • Detection of AP failures: • Beacon-frame monitoring • Signal-to-noise ratio • Recover from AP failures: • Access-Point Replication • Overlapping-Coverage • Link-Multiplexing 4 / 15

5. Related Work - Location Discovery • Due to the small cell sizes in WLAN, if we can identify the AP that a MN accesses currently, we can determine that the MN is in the neighborhood of the AP. • Obtain MN’s MAC address & associated AP’s IP address : • RADIUS • SNMP polling • SNMP traps • MN’s MAC-to-IP address mapping (for pushing message): • DHCP • Default Router 5 / 15

6. Association Trap: Insert a new record to store the MAC address of a mobile client and the ID of the AP that sent the trap. • Reassociation Trap: Update the AP ID field of the record that has an MAC address same as the one shown in the reassociation trap. • Disassociation Trap: Delete the record that has an MAC address same as the one shown in the disassociation trap. Introduction - SNMP traps • The IEEE 802.11 standard defines three association-related services: Association, Reassociation, and Disassociation. • All APs send SNMP traps to report the association-related events occurring in the APs. 6 / 15

7. Introduction - Default Router • Using the AP’s IP, search [Subnet Mask] & [Subnet ID] • Send an SNMP get-request to the AP to get its [Subnet Mask] ( in the ipAdEntNetMask object of the ipAddrTable table ) • [Subnet ID] = (AP’s IP) bit-wised AND ( [Subnet Mask] ) 7 / 15

8. Introduction - Default Router (cont.) • Find [Default Router] of MN/AP • In ipRouteTable table, the entry with a value of 0.0.0.0 in the ipRouteDest object indicates a default route. The ipRouteNextHop object in the default route entry will be the IP address of the default router. • Find corresponding [Interface Index] • From the ipAdEntIfIndex object in the ipAddrTable table • Use Get-Next-requests to perform an IP address search in the ipNetToMediaTable table of the default router until the IP address is found. • To avoid retrieving the entire ipNetToMediaTable table, we use [Interface Index] and the [Subnet ID] of the subnet table as the start instance identifier of SNMP queries. 8 / 15

9. 3 AP-Association table: [AP's IP]、[MN's MAC] 、[MN's IP] AP-Information table: [AP's IP]、[x coordinate]、[y coordinate]、[AP's state ] 4 1 Location-Map: 320x240.jpg 2 Implementation • MN association AP： • AP notify SERVER（MN’s MAC、AP’s IP） • SERVER obtain MN’s IP • Add a record to「AP-Association table」（associated [AP’s IP] & [MN’s MAC] & [MN’s IP]） • SERVER push data to MN • If MN w/o「Location-Map」or 「Location-Map」revised Push「Location-Map」&「AP-Information table」& associated [AP’s IP] • Else Push「AP-Information table」& associated [AP’s IP] 9 / 15

10. 2 AP-Association table: [AP's IP]、[MN's MAC] 、[MN's IP] AP-Information table: [AP's IP]、[x coordinate]、[y coordinate]、[AP's state ] 3 1 Location-Map: 320x240.jpg Implementation (cont.) • MN reassociation AP • AP notify SERVER（MN’s MAC、AP’s IP） • Update record in「AP-Association table」（search the record with same [MN’s MAC] and update corresponding [AP’s IP] to reassociated AP’s IP） • SERVER push reassociated [AP’s IP] to MN 10 / 15

11. 2 AP-Association table: [AP's IP]、[MN's MAC] 、[MN's IP] AP-Information table: [AP's IP]、[x coordinate]、[y coordinate]、[AP's state ] 3 1 Location-Map: 320x240.jpg Implementation (cont.) • MN disassociation AP • AP notify SERVER（MN’s MAC、AP’s IP） • Delete record in「AP-Association table」（search the record with same [MN’s MAC] , if disassociated AP’s IP = [AP’s IP] then deletethe record） • SERVER push disassociated [AP’s IP] to MN 11 / 15

12. AP-Association table: [AP's IP]、[MN's MAC] 、[MN's IP] AP-Information table: [AP's IP]、[x coordinate]、[y coordinate]、[AP's state ] Location-Map: 320x240.jpg Implementation (cont.) • SERVER periodic check all APs state（ping all [AP's IP] in「AP- Information table」） • If AP state change（Fault or Recovery） • Update corresponding [AP’s state] in「AP- Information table」 • SERVER push changed AP state (x, y, state) to all [MN's IP] in「AP-Association table」 12 / 15

13. Implementation (cont.) • MN receive pushed message from SERVER（process in background） • 「Location-Map」&「AP-Information table」： Paste all APs icon to corresponding coordinate in Location-Map（according to the AP state） • Associated or Reassociated [AP's IP] : Add a circle on corresponding AP icon in「Location-Map」 • Disassociated [AP's IP] : Remove circle on corresponding AP icon in「Location-Map」 • Changed AP state : Change corresponding AP icon in「Location-Map」 • MN detect associated AP fault（internet disconnect or SNR drops suddenly or can't detect beacon-frame） • Pop-up「Location-Map」and change associated AP icon • Suggest that user move to the nearest normal AP 13 / 15

14. Conclusion • This novel approach for tolerating AP Failures: • Don’t require additional hardware (redundant AP/NIC or RADIUS server) • Can obtain most up-to-date MNs associated with APs • Server push AP state to MN actively only AP’s state to be changed: to save MN’s battery power & available bandwidth • Additional function: ad information • Only need: • A server on DS (can combine with other existing server) • Location-Map • Keep AP’s information (IP, coordinate) and detect AP’s state • Obtain MN & associated AP’s IP address • Push message to MN • A push user agent in the MN • Receive pushed message from server • When AP fault, suggest user that move to the nearest normal AP 14 / 15

15. Future Work • SNMP Instructions • Push Algorithm • Support protocols in Access-Point • Papers about Access-Point • MN’s MAC-to-IP Address Mapping • Experiment & Analysis 15 / 15