Research Plan : A Novel Approach for Tolerating Access-Point Failures

Reporter ： Mark Yang

93.05.25

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Outline

Abstract Related Work Introduction Implementation Conclusion Future Work

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Abstract

A novel approach for tolerating Access-Point Failures.

13:00 ～ 14:00限時搶購．全面 6

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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

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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

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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.

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.

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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] )

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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.

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Implementation

MN association AP：1) AP notify SERVER （ MN’s MAC 、 AP’s IP）2) SERVER obtain MN’s IP3) Add a record to「 AP-Association table」（ associated [AP’s IP] &

[MN’s MAC] & [MN’s IP]）4) 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]

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

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Implementation (cont.)

MN reassociation AP1) AP notify SERVER （ MN’s MAC 、 AP’s IP ）2) 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）

3) SERVER push reassociated [AP’s IP] to MN

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

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Implementation (cont.)

MN disassociation AP1) AP notify SERVER （ MN’s MAC 、 AP’s IP ）2) Delete record in 「 AP-Association table」（ search the record with

same [MN’s MAC] , if disassociated AP’s IP = [AP’s IP] then delete the record）

3) SERVER push disassociated [AP’s IP] to MN

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

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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 」

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

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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

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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

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Future Work

SNMP Instructions Push Algorithm Support protocols in Access-Point Papers about Access-Point MN’s MAC-to-IP Address Mapping Experiment & Analysis