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

• US 20060187873A1
• Filed: 07/15/2005
• Published: 08/24/2006
• 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 7,805,140 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04W 12/062 Pre-authentication
• 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 for communicating with an access element;

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

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

if the signal attribute crosses a threshold value, alternate between a pre-emptive scanning mode to scan for access elements with which to associate, 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 signal attribute is the signal to noise ratio.

3. 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

receive a roaming list identifying at least one access element;

and

scan for the at least one access element on the roaming list during the pre-emptive roaming mode.

4. The wireless client of claim 1 wherein, to monitor the signal transmitted by the first access element, 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 the 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 3 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 point, perform a scan of a plurality of frequency channels to identify available access points 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 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 wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to

select an access element identified in the pre-emptive scanning mode;

and

associate with the selected access element.

8. The wireless client of claim 7 wherein the selection of the access element is based at least in part on signal information gathered during the preemptive scanning mode.

9. The wireless client of claim 7 wherein the selection of the access element is based at least in part on load information obtained from the access elements.

10. The wireless client of claim 7 wherein each access point identified during the preemptive scanning mode identifies a central control element;

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

11. A method for facilitating roaming in wireless networks, comprising

monitoring, during an associated state with a first access element, radio frequency signals transmitted by the first access element relative to a signal attribute;

and

if the signal attribute crosses a threshold value, alternating between a pre-emptive scanning mode to scan for access elements with which to associate, 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 signal attribute is the signal to noise ratio.

13. The method of claim 11 further comprising

receiving a roaming list identifying at least one access element;

and

scanning for the at least one access element on the roaming list during the pre-emptive roaming mode.

14. The method of claim 11 further comprising

measuring the signal attribute of the 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 14 further comprising

performing, if connectivity is lost with the first access point, a scan of a plurality of frequency channels to identify available access points with which to associate.

16. The method of claim 15 further comprising

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

transmitting an association request to the selected access element; and

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

17. The method of claim 11 further comprising

selecting an access element identified in the pre-emptive scanning mode;

and

associate with the selected access element.

18. The method of claim 17 wherein the selection of the access element is based at least in part on signal information gathered during the preemptive scanning mode.

19. The method of claim 17 wherein the selection of the access element is based at least in part on load information obtained from the access elements.

20. An apparatus facilitating roaming in wireless networks, comprising

means for wirelessly communicating with an access element;

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

means for alternating between a pre-emptive scanning mode to scan for access elements with which to associate, and a traffic mode to communicate with the first access element to transmit or receive wireless frames, if the signal attribute crosses a threshold value.

21. A wireless network access device operative to facilitate roaming in wireless networks, comprising

a wireless network interface for communicating with a wireless client;

a processor;

a memory;

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

receive an association request from a wireless client;

determine a roaming list for the wireless client, wherein the roaming list identifies at least one wireless network access device;

transmit the roaming list to the wireless client.

22. The wireless network access device of claim 21 wherein the roaming list is appended to an association response transmitted to the wireless client in response to the association request.

23. The wireless network access device of claim 21 wherein the wireless network access application further comprises instructions operable to cause the processor and the wireless network interface to

measure the radio frequency signals corresponding to wireless frames transmitted by the wireless client relative to a signal attribute;

and

transmit the measured signal attribute information to a network device.

24. The wireless network access device of claim 23 wherein the network device is a central control element.

25. The wireless network access device of claim 23 wherein the network device is a central management platform.

26. The wireless network access device of claim 21 wherein the wireless network access device is one of a plurality of network access devices operably associated with a central control element;

and wherein the roaming list is based at least in part on the plurality of network access devices associated with the central control element.

27. The wireless network access device of claim 21 wherein the roaming list is a statically defined list of wireless network access devices.

28. The wireless network access device of claim 21 wherein the wireless network access device supports an RF coverage area having a perimeter;

and wherein the roaming list comprises a list of wireless network access devices located proximally to the perimeter of the coverage area associated with the wireless network access device.

29. The wireless network access device of claim 21 wherein the wireless network access application further comprises instructions operable to cause the processor and the wireless network interface to

receive a list of access elements detected by the wireless client;

and wherein the roaming list is determined at least in part based on the received list of access elements.

30. A method facilitating roaming in wireless networks, comprising

receiving an association request from a wireless client;

determining a roaming list for the wireless client, wherein the roaming list identifies at least one wireless network access device; and

transmitting the roaming list to the wireless client.

31. The method of claim 30 further comprising

transmitting an association response to the wireless client, wherein the roaming list is appended to the association response.

32. The method of claim 30 further comprising

measuring the radio frequency signals corresponding to wireless frames transmitted by the wireless client relative to a signal attribute;

and

transmitting the measured signal attribute information to a network device.

33. The method of claim 30 further comprising

receiving a list of wireless network access devices detected by the wireless client;

and wherein the roaming list is determined at least in part based on the received list of wireless network access devices.

34. A wireless network access device operative to facilitate roaming in wireless networks, comprising

means for wireless communicating with a wireless client;

means for receiving an association request from a wireless client;

means for determining a roaming list for the wireless client, wherein the roaming list identifies at least one wireless network access device; and

means for transmitting the roaming list to the wireless client.

35. A wireless network system facilitating roaming in a wireless network environment, comprising

a plurality of access elements for wireless communication with at least one wireless client and for communication with a central control element;

wherein the access elements are each operative to

establish and maintain, in connection with a central control element, wireless connections with wireless clients;

transmit received wireless frames to a central control element;

at least one central control element for supervising the access elements, wherein the central control element is operative to

manage wireless connections between the access elements and corresponding wireless clients, and

receive, through an access element, an association request from a wireless client;

determine a roaming list for the wireless client, wherein the roaming list identifies at least one access element;

transmit, through the access element, the roaming list to the wireless client.

36. The wireless network system of claim 35 wherein at least one access element is operative to

detect the strength of RF signals-from wireless clients;

and

append a signal strength value to wireless frames received from wireless clients; and

wherein the central control element is operative to

store signal strength data appended to frames transmitted by the plurality of access elements in association with wireless client identifiers; and

wherein the roaming list is determined at least in part based on the signal strength data corresponding to the wireless client.