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

• US 7,805,140 B2
• Filed: 07/15/2005
• Issued: 09/28/2010
• Est. Priority Date: 02/18/2005
• Status: Expired due to Fees

• 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): Corsaro; Nick
• Assistant Examiner(s): Ajayi; Joel
• Application Number:
  US11/182,264
• Publication Number:
  US 20060187873A1
• Time in Patent Office: 1,901 Days
• Field of Search: None
• US Class Current: 455/436
• 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 for communicating with one or more access elements;

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, 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;

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 below a threshold value, then alternate 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;

select the second access element; and

associate with the selected second access element;

the instructions are operable to cause the processor and the wireless network interface to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second access element identified during the pre-emptive scanning mode.

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 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.

7. 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.

8. 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.

29. The wireless client of claim 1 wherein the wireless client is further operable to:

receive a signal-to-noise ratio (SNR) threshold value from the first access element; and

use the SNR threshold value to determine whether to alternate between the pre-emptive scanning mode and the traffic mode.

30. The wireless client of claim 1, wherein, when alternating between the pre-emptive scanning mode and the traffic mode, the wireless network interface driver application further comprises instructions operable to cause the processor and the wireless network interface to:

operate according to the pre-emptive scanning mode during a first time interval; and

operate according to the traffic mode during a second time interval.

31. The wireless client of claim 30, wherein the first time interval and the second time interval are each not greater than 300 milliseconds.

32. The wireless client of claim 31, wherein the first time interval is approximately 50 milliseconds and the second time interval is approximately 25 milliseconds.

33. The wireless client of claim 1, wherein the roaming list is dynamically determined in response to the association request 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, 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 device;

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 that the monitored signal attribute crosses below a threshold value, then alternate 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;

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

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

the wireless client device is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second access element identified during the pre-emptive scanning mode.

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

15. The method of claim 9 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.

16. 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, 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 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;

the apparatus is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second access element identified during the pre-emptive scanning mode.

17. A wireless network access device, comprising:

a wireless network interface for communicating with one or more wireless clients;

a processor;

a memory; and

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, the association request identifies one or more other wireless network access devices discovered by the wireless client;

generate a roaming list for the wireless client in response to the association request, the roaming list identifies at least one candidate wireless network access device among the one or more other wireless network access devices identified in the association request;

append the roaming list to an association response; and

transmit the association response with the roaming list to the wireless client

the wireless client is configured to;

receive the roaming list from the wireless network access device;

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

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

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

a traffic mode to communicate with the wireless network access device from which the wireless client received the roaming list to transmit or receive wireless frames; and

when a second wireless network access device of the one or more candidate wireless network access devices having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the wireless network access device from which the wireless client received the roaming list by at least a predetermined margin is identified during a scan for candidate wireless network access devices while in the pre-emptive scanning mode;

select the second wireless network access device; and

associate with the selected second wireless network access device;

the wireless client is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second wireless network access device identified during the pre-emptive scanning mode.

18. The wireless network access device of claim 17 wherein the wireless network access application further comprises instructions operable to cause the processor and the wireless network interface to:

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

generate measured signal attribute information based on the one or more measured radio frequency signals; and

transmit the measured signal attribute information to a central network device.

19. The wireless network access device of claim 18 wherein the central network device is a central control element.

20. The wireless network access device of claim 18 wherein the central network device is a central management platform.

21. The wireless network access device of claim 17 wherein the wireless network access device is one of a plurality of wireless network access devices operably associated with a central control element;

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

28. The wireless network access device of claim 17 wherein the wireless network access application further comprises instructions operable to cause the processor and the wireless network interface to

advertise a signal-to-noise ratio (SNR) threshold usable by the wireless client to determine whether to enter a pre-emptive scanning mode.

22. A method, comprising:

receiving, by a wireless network access device, an association request from a wireless client, the association request identifies one or more other wireless network access devices discovered by the wireless client;

generating, by the wireless network access device, a roaming list for the wireless client in response to the association request, the roaming list identifies at least one candidate wireless network access device among the one or more other wireless network access devices identified in the association request;

appending, by the wireless network access device, the roaming list to an association response; and

transmitting the association response with the roaming list to the wireless client;

the wireless client is configured to;

receive the roaming list from the wireless network access device;

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

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

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

a traffic mode to communicate with the wireless network access device from which the wireless client received the roaming list to transmit or receive wireless frames; and

when a second wireless network access device of the one or more candidate wireless network access devices having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the wireless network access device from which the wireless client received the roaming list by at least a predetermined margin is identified during a scan for candidate wireless network access devices while in the pre-emptive scanning mode;

select the second wireless network access device; and

associate with the selected second wireless network access device;

the wireless client is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second wireless network access device identified during the pre-emptive scanning mode.

23. The method of claim 22 further comprising:

measuring, by the wireless network access device, one or more radio frequency signals corresponding to wireless frames transmitted by the wireless client relative to a signal attribute;

generating, by the wireless network access device, measured signal attribute information based on the one or more measured radio frequency signals; and

transmitting the measured signal attribute information to a central network device.

24. The method of claim 22 wherein the wireless network access device is one of a plurality of wireless network access devices operably associated with a central control element;

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

25. A wireless network access device, comprising:

means for wirelessly communicating with a wireless client;

means for receiving an association request from the wireless client, the association request identifies one or more other wireless network access devices discovered by the wireless client;

means for generating a roaming list for the wireless client in response to the association request, the roaming list identifies at least one candidate wireless network access device among the one or more other wireless network access devices identified in the association request;

means for appending the roaming list to an association response; and

means for transmitting the association response with the roaming list to the wireless client;

the wireless client is configured to;

receive the roaming list from the wireless network access device;

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

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

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

a traffic mode to communicate with the wireless network access device from which the wireless client received the roaming list to transmit or receive wireless frames; and

when a second wireless network access device of the one or more candidate wireless network access devices having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the wireless network access device from which the wireless client received the roaming list by at least a predetermined margin is identified during a scan for candidate wireless network access devices while in the pre-emptive scanning mode;

select the second wireless network access device; and

associate with the selected second wireless network access device;

the wireless client is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second wireless network access device identified during the pre-emptive scanning mode.

26. A wireless network system, comprising:

a plurality of access elements each operative to wirelessly communicate with at least one wireless client and to communicate with a respective central control element, the access elements are each operative to;

establish and maintain, in connection with a respective central control element, one or more wireless connections with one or more respective wireless clients;

transmit wireless frames received from the one or more respective wireless clients to the respective central control element; and

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

manage one or more wireless connections between one or more of the plurality of access elements and one or more respective wireless clients, and

receive, through a first one of the plurality of access elements, an association request from a first one of the one or more respective wireless clients associated with the first one of the plurality of access elements, the association request identifies one or more other access elements of the plurality of access elements discovered by the first one of the wireless clients;

determine a roaming list for the first one of the wireless clients in response to the association request, the roaming list identifies at least one candidate access element among the one or more other access elements identified in the association request;

append the roaming list to an association response; and

transmit, through the first one of the access elements, the association response with the roaming list to the first one of the wireless clients;

the first one of the wireless clients is configured to;

receive the roaming list from the first one of the access elements;

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

when the first one of the wireless clients determines that the monitored signal attribute crosses below a threshold value, then alternate 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 one of the access elements to transmit or receive wireless frames; and

when a second one of the access elements 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 one of the access elements 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 one of the access elements; and

associate with the selected second one of the access elements;

the first one of the wireless clients is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second one of the access elements identified during the pre-emptive scanning mode.

27. The wireless network system of claim 26 wherein at least one access element of the plurality of access elements is operative to

detect the strength of one or more radio frequency signals received from one or more respective wireless clients;

and

append a signal strength value to one or more wireless frames received from one or more of the one or more respective wireless clients; and

wherein the central control element is operative to store signal strength values appended to frames and transmitted by the plurality of access elements in association with wireless client identifiers corresponding to the wireless clients from which the wireless frames were received by the respective access elements; and

wherein the roaming list is determined at least in part based on one or more signal strength values corresponding to the first one of the wireless clients.

34. A wireless network system, comprising:

one or more access points, each of the access points is operative to service one or more wireless clients for their wireless communications; and

one or more control elements, each of the control elements is operative to manage one or more of the access points for their connections with the wireless clients,

during associations with the wireless clients, between each one of the access points and a particular one of the control elements that manages the access point;

the access point is operative to;

receive an association request from a wireless client, the association request comprises one or more of the access points discovered by the wireless client; and

forward the association request to the control element; and

the control element is operative to;

receive the association request from the access point;

exchange and synchronize information regarding the wireless client with the other ones of the control elements;

store the information regarding the wireless client;

construct a roaming list based at least in part on the access points in the association request and the information regarding the wireless client; and

transmit an association response to the wireless client, the association response comprises the roaming list

the wireless client is configured to;

receive the roaming list from the access point;

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

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

 

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

 

a traffic mode to communicate with the access point from which the wireless client received the roaming list to transmit or receive wireless frames; and

when a second access point of the one or more candidate access points having a value of the monitored signal attribute greater than the value of the monitored signal attribute of the access point from which the wireless client received the roaming list by at least a predetermined margin is identified during a scan for candidate access points while in the pre-emptive scanning mode;

 

select the second access point; and

 

associate with the selected second access point;

the wireless client is configured to alternate between the pre-emptive scanning mode and the traffic mode at least a plurality of times before selecting the second access point identified during the pre-emptive scanning mode.