Pre-Emptive Roaming Mechanism Allowing for Enhanced QoS in Wireless Network Environment

• US 20100322198A1
• Filed: 09/01/2010
• Published: 12/23/2010
• Est. Priority Date: 02/18/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Friday, Robert J., Dietrich, Paul F.
• Granted Patent: US 8,798,018 B2
• Time in Patent Office: Days
• US Class Current: 370/332
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

A preemptive roaming mechanism in wireless network environments. In one implementation, the present invention provides a wireless client that implements a preemptive roaming mode that, when an attribute of the signal (e.g., Signal to Noise Ratio (SNR), etc.) between the access point with which the client is currently associated crosses a threshold, scans for other access points with which to associate. In one implementation, the client switches between the scanning mode and a traffic mode to allow data to be transferred between the client and the current access point. The pre-emptive roaming functionality can be configured to support desired data rates or other QoS levels.

Claims

1. A wireless client, comprising:

a wireless network interface;

a processor;

a memory;

a wireless network interface driver application, stored in the memory, comprising instructions operable to cause the processor and the wireless network interface to;

receive, from a first access element, a roaming list identifying at least one candidate access element of one or more candidate access elements other than the first access element, wherein the roaming list is transmitted from the first access element to the wireless client in connection with an association between the first access element and the wireless client;

monitor, during an associated state with the first access element, one or more radio frequency signals transmitted by the first access element relative to a signal attribute; and

when the wireless client determines that the monitored signal attribute crosses a threshold value, then alternate between

a pre-emptive scanning mode to actively scan for the one or more candidate access elements identified in the roaming list with which to associate by sending directed probes to the one or more candidate access elements identified in the roaming list, and

a traffic mode to communicate with the first access element to transmit or receive wireless frames.

2. The wireless client of claim 1 wherein the wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to:

when a second access element of the one or more candidate access elements having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the first access element by at least a predetermined margin is identified during a scan for candidate access elements while in the pre-emptive scanning mode;

select the second access element; and

associate with the selected second access element.

3. The wireless client of claim 1 wherein the signal attribute is signal-to-noise ratio (SNR).

4. The wireless client of claim 1 wherein, to monitor the one or more radio frequency signals transmitted by the first access element and to determine whether the monitored signal attribute crosses a threshold value, the wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to:

measure the signal attribute of each of one or more radio frequency signals corresponding to wireless frames transmitted by the first access element;

apply a filter to the measured signal attributes; and

compare the filtered signal attributes to the threshold value.

5. The wireless client of claim 1 wherein the wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to:

if connectivity is lost with the first access element, perform a scan of a plurality of frequency channels to identify available access elements with which to associate.

6. The wireless client of claim 5 wherein the wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to:

select an access element identified during the scan of the plurality of frequency channels;

transmit an association request to the selected access element; and

transmit to the selected access element a list of access elements detected during the scan of the plurality of frequency channels.

7. The wireless client of claim 1 wherein the selection of the second access element is based at least in part on signal information gathered during the pre-emptive scanning mode.

8. The wireless client of claim 1 wherein the selection of the second access element is based at least in part on load information obtained from the one or more candidate access elements scanned during the pre-emptive scanning mode.

9. The wireless client of claim 1 wherein each access element scanned during the preemptive scanning mode identifies a central control element;

and wherein the selection of the second access element is based at least in part on the central control element identified by the second access element.

10. The wireless client of claim 1 wherein the roaming list is appended to an association response transmitted from the first access element to the wireless client in response to an association request transmitted from the wireless client.

11. A method, comprising:

receiving from a first access element, by a wireless client device, a roaming list identifying at least one candidate access element of one or more candidate access elements other than the first access element, wherein the roaming list is transmitted from the first access element to the wireless client in connection with an association between the first access element and the wireless client;

monitoring, by the wireless client device, during an associated state with the first access element, one or more radio frequency signals transmitted by the first access element relative to a signal attribute; and

when it is determined by the wireless client device that the monitored signal attribute crosses a threshold value, then alternating between

a pre-emptive scanning mode to actively scan for one or more candidate access elements identified in the roaming list with which to associate by sending directed probes to the one or more candidate access elements identified in the roaming list, and

a traffic mode to communicate with the first access element to transmit or receive wireless frames.

12. The method of claim 11 wherein the method further comprises when a second access element of the one or more candidate access elements having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the first access element by at least a predetermined margin is identified during a scan for candidate access elements while in the pre-emptive scanning mode:

selecting, by the wireless client device, the second access element; and

associating, by the wireless client device, with the selected second access element.

13. The method of claim 11 wherein the signal attribute is signal-to-noise ratio (SNR).

14. The method of claim 11 wherein monitoring one or more radio frequency signals transmitted by the first access element and determining whether the monitored signal attribute crosses the threshold value comprises:

measuring the signal attribute of each of one or more radio frequency signals corresponding to wireless frames transmitted by the first access element;

applying a filter to the measured signal attributes, and

comparing the filtered signal attributes to the threshold value.

15. The method of claim 11 further comprising, if connectivity is lost with the first access element, performing, by the wireless client device, a scan of a plurality of frequency channels to identify available access elements with which to associate.

16. The method of claim 15 further comprising:

selecting, by the wireless client device, an access element identified during the scan of the plurality of frequency channels;

transmitting, by the wireless client device, an association request to the selected access element; and

transmitting, by the wireless client device, to the selected access element a list of access elements detected during the scan of the plurality of frequency channels.

17. The method of claim 11 wherein the selection of the second access element is based at least in part on signal information gathered during the pre-emptive scanning mode.

18. The method of claim 11 wherein the selection of the second access element is based at least in part on load information obtained from the one or more candidate access elements scanned during the pre-emptive scanning mode.

19. The method of claim 11 wherein each access element scanned during the preemptive scanning mode identifies a central control element;

and wherein the selection of the second access element is based at least in part on the central control element identified by the second access element.

20. An apparatus, comprising:

means for wirelessly communicating with one or more access elements;

means for receiving from a first access element a roaming list identifying at least one candidate access element of one or more candidate access elements other than the first access element, wherein the roaming list is transmitted from the first access element to the wireless client in connection with an association between the first access element and the apparatus;

means for monitoring, during an associated state with the first access element, one or more radio frequency signals transmitted by the first access element relative to a signal attribute; and

means for alternating, when the signal attribute crosses below a threshold value, between

a pre-emptive scanning mode to actively scan for one or more candidate access elements identified in the roaming list with which to associate by sending directed probes to the one or more candidate access elements identified in the roaming list, and

a traffic mode to communicate with the first access element to transmit or receive wireless frames; and

when a second access element of the one or more candidate access elements having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the first access element by at least a predetermined margin is identified during a scan for candidate access elements while in the pre-emptive scanning mode;

means for selecting the second access element; and

means for associating with the selected second access element.