Pre-emptive roaming mechanism allowing for enhanced QoS in wireless network environments

• US 8,798,018 B2
• Filed: 09/01/2010
• Issued: 08/05/2014
• 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.
• Primary Examiner(s): Hamza, Faruk
• Assistant Examiner(s): LO, DIANE LEE
• Application Number:
  US12/873,987
• Publication Number:
  US 20100322198A1
• Time in Patent Office: 1,434 Days
• Field of Search: None
• US Class Current: 370/338
• 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;

when the wireless client determines that the monitored signal attribute crosses a threshold value, then alternate, at least a plurality of times, 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;

receive a response from at least a portion of the one or more candidate access elements;

for each of one or more of the candidate access elements from which the response was received, group the candidate access element into one of a plurality of groups, the grouping being based at least on a load threshold of the candidate access element and either a switch identifier of the candidate access element or a resiliency identifier of the candidate access element, the plurality of groups being ranked; and

attempt to associate with one of the candidate access elements grouped into the highest ranked group.

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

3. 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.

4. 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.

5. The wireless client of claim 4 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.

6. The wireless client of claim 5 wherein the selection of the selected access element is based at least in part on signal information gathered during the pre-emptive scanning mode.

7. The wireless client of claim 5 wherein the selection of the selected 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.

8. 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.

9. 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;

when it is determined by the wireless client device that the monitored signal attribute crosses a threshold value, then alternating, at least a plurality of times, 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;

receiving a response from at least a portion of the one or more candidate access elements;

for each of one or more of the candidate access elements from which the response was received, grouping the candidate access element into one of a plurality of groups, the grouping being based at least on a load threshold of the candidate access element and either switch identifier of the candidate access element or a resiliency identifier of the candidate access element, the plurality of groups being ranked; and

attempting to associate with one of the candidate access elements grouped into the highest ranked group.

10. The method of claim 9 wherein the signal attribute is signal-to-noise ratio (SNR).

11. The method of claim 9 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.

12. The method of claim 9 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.

13. The method of claim 12 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.

14. The method of claim 13 wherein the selection of the selected access element is based at least in part on signal information gathered during the preemptive scanning mode.

15. The method of claim 13 wherein the selection of the selected 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.

16. The method of claim 13 wherein each access element scanned during the preemptive scanning mode identifies a central control element;

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

17. 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;

means for alternating, when the signal attribute crosses below a threshold value, at least a plurality of times 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;

means for receiving a response from at least a portion of the one or more candidate access elements;

for each of one or more of the candidate access elements from which the response was received, means for grouping the candidate access element into one of a plurality of groups, the grouping being based at least on a load threshold of the candidate access element and either a switch identifier of the candidate access element or a resiliency identifier of the candidate access element, the plurality of groups being ranked; and

means for attempting to associate with one of the candidate access elements grouped onto the highest ranked group.