WO2017011091A1

WO2017011091A1 - Method of, and arrangement for, enhancing scan and roam performance of a mobile client by retrieving scan and roam parameters of access points connected to a distribution system

Info

Publication number: WO2017011091A1
Application number: PCT/US2016/035985
Authority: WO
Inventors: Yadukishore KODICHERLA; Rajiv Shirirang JOSHI; Raj Kiran; Sandeep Ramakrishnan; Mark LUKSICH; Marco Belli; Rajendiran SUBRAMANI
Original assignee: Symbol Technologies, Llc
Priority date: 2015-07-10
Filing date: 2016-06-06
Publication date: 2017-01-19

Abstract

A mobile client exchanging data with a current access point (AP) retrieves scan and roam parameters from other APs by discovering candidate APs that are available for roaming, combining information from the candidate APs to construct an aggregated scan assist (SA) parameter request frame, and sending the aggregated SA parameter request frame to an SA handler. The SA handler sends an individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP, receives an individual SA parameter response message from each candidate AP, and forwards either an aggregated or an individual SA parameter response frame to the client. The client selects a target AP from the candidate APs based on the parameter response frame, and exchanges data with the target AP after roaming.

Description

METHOD OF, AND ARRANGEMENT FOR, ENHANCING SCAN AND ROAM PERFORMANCE OF A MOBILE CLIENT BY RETRIEVING SCAN AND ROAM PARAMETERS OF ACCESS POINTS CONNECTED TO A

DISTRIBUTION SYSTEM

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a distribution system (DS) having a plurality of interconnected access points (APs) and a mobile client that wants to roam between one of the APs (current AP) with which the client is currently exchanging data, to one of the other APs (target AP) to which the client wishes to exchange data after roaming, and, more particularly, to a method of, and an arrangement for, enhancing scan and roam performance of the mobile client by retrieving scan and roam parameters, such as channel information and/or information elements (IEs), from the other APs, especially in delay-sensitive communications applications, such as Internet Protocol (IP) networks over which voice and/or video (VoIP) are carried.

[0002] In accordance with the Institute of Electrical and Electronics Engineers

(IEEE) 802.11 standard of specifications for a wireless local area network (LAN) or distribution system (DS) having a plurality of interconnected access points (APs), normally wireless routers, it is known for a mobile, wireless communications client, e.g., a smartphone, a tablet, a laptop or portable computer, a personal digital assistant, a wearable communications device, a handheld and/or vehicular radio, or an analogous supplicant device, to securely exchange voice and/or video communications data with one of the APs (current AP), after authentication, association, and key derivation, over at least one communications channel, i.e., a designated frequency band in the radio communications spectrum. Certain channels, however, particularly in the 5.15 GHz to 5.85 GHz band, are shared by certain radar systems, such as weather, airport, road, industrial, and military radars. These radar systems generate mission-critical radar signals that are granted a higher transmission priority than wireless LAN communications by governmental regulation. As a result, in accordance with the known dynamic frequency selection (DFS) protocol, which allows wireless LANs to coexist with radar systems without interference, each wireless device, i.e., each AP and the client, must be able to sense the presence of a radar signal on a particular channel or channels, and then take action to insure that the client does not use that channel for communications if a radar signal is present.

[0003] More particularly, in accordance with the DFS protocol, the client must passively scan the channels, one at a time, typically for about 105ms, and listen either for beacons sent periodically by the APs on each channel, or for probe responses sent by the APs on each channel. The client is not permitted to actively scan any DFS channel on which a radar signal is present. Even if there is no radar signal on the DFS channel and the client heard a beacon during the passive scan on that channel, then the client can actively scan on the channel for a maximum period of ten seconds from the point of time that it heard the beacon. The time taken to successively passively scan multiple channels is significant for VoIP applications where a delay on the order of fifty milliseconds is generally considered the highest amount of delay that can be introduced and tolerated in a voice call or video session.

[0004] When the client moves from the current AP, generally referred to as roaming, and wishes to exchange data with another of the APs (target AP) whose transmission signal quality is better than that of the current AP, then the client must be sure that there is no radar signal on the channel of the target AP. However, this involves passively scanning all the channels, one after another, typically for about 105ms each, as described above, in order to find the candidate APs and select the channel having no radar signal and the best transmission signal quality. Again, the time taken to successively passively scan multiple channels negatively impacts on the roam handoff time and can interrupt the continuity of the voice call or video session.

[0005] Accordingly, there is a need to avoid passively scanning multiple channels, to retrieve the capabilities of the other APs without doing a scan, and to enhance roaming performance of a mobile client that is roaming between APs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0006] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments. [0007] FIG. 1 is a circuit topology of an arrangement by which a mobile client retrieves AP parameters from other APs over a DS in accordance with the present disclosure.

[0008] FIG. 2 is a connection and time sequence diagram of the arrangement of FIG. 1 in which the retrieved AP parameters are channels in accordance with the present disclosure.

[0009] FIG. 3 is a connection and time sequence diagram of the arrangement of FIG. 1 in which the retrieved AP parameters are IEs in accordance with the present disclosure.

[0010] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

[0011] The method and arrangement components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION

[0012] One aspect of the present disclosure generally relates to a distribution system (DS) having a mobile client, e.g., a smartphone, a tablet, a laptop or portable computer, a personal digital assistant, a wearable communications device, a handheld and/or vehicular radio, or an analogous supplicant device, wanting to roam away from a current access point (AP) with which the client is currently exchanging data, and, more particularly, to a method of enhancing scan and roam performance by retrieving scan and roam parameters, e.g., channel information and/or information elements (IEs), from other APs interconnected with the current AP over the DS. The method is performed by the client discovering candidate APs that are available for roaming from among the other APs, by the client combining information from the candidate APs to construct an aggregated scan assist (SA) parameter request frame, and by the client sending the aggregated SA parameter request frame to an SA handler over a wireless connection. The SA handler is preferably located in the current AP, but may be located in one of the other APs, or a controller of the DS, or the DS, or in the cloud. The SA handler sends an individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, receives an individual SA parameter response message from each candidate AP over the DS, and forwards either individual SA parameter response frames, or an aggregated SA parameter response frame, to the client over the wireless connection. The client also selects a target AP from the candidate APs based on the SA parameter response frame(s), and exchanges data with the target AP after roaming.

[0013] When the scan and roam parameters to be retrieved include channel information of the other APs, a plurality of the channels are dynamic frequency selection (DFS) channels designated to carry radar signals of higher priority than the data exchanged by the client. In this case, the SA handler forwards individual SA parameter response frames based on the individual SA parameter response messages to the client. The client determines the absence of radar signals on the DFS channels based on the individual SA parameter response frames, sends probe request frames on the DFS channels having no radar signals, receives probe response frames on the DFS channels having no radar signals, roams, and exchanges data with the target AP over one of the DFS channels having no radar signals. In one embodiment, the client itself will periodically send the aggregated SA parameter request frame to the SA handler over the wireless connection, and then the SA handler, as before, sends the individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, receives the individual SA parameter response message from each candidate AP over the DS, and forwards the individual SA parameter response frames to the client over the wireless connection in response to each aggregated SA parameter request frame sent by the client. In another embodiment, the client sends the aggregated SA parameter request frame to the SA handler over the wireless connection with a request for unsolicited periodic parameter response messages from the other APs, and the SA handler sends the individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, receives the periodic individual SA parameter response message from each candidate AP over the DS, and forwards the periodic individual SA parameter response messages over the wireless connection.

[0014] When the scan and roam parameters to be retrieved are IEs of the other

APs, the SA handler combines the individual SA parameter response messages to construct an aggregated SA parameter response frame, and sends the aggregated SA parameter response frame to the client. The client then uses the retrieved IEs for various purposes, such as selecting the target AP.

[0015] Still another aspect of the present disclosure relates to an arrangement for enhancing scan and roam performance by retrieving scan and roam parameters in a distribution system (DS) having a plurality of interconnected APs, a mobile client currently exchanging data with one of the APs (current AP) and wanting to roam away from the current AP, and a scan assist (SA) handler. The client is configured to discover candidate APs that are available for roaming from among others of the APs, and to combine information from the candidate APs to construct an aggregated SA parameter request frame. The SA handler is configured to receive the aggregated SA parameter request frame sent by the client over a wireless connection, to send an individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, to receive an individual SA parameter response message from each candidate AP over the DS, and to forward either individual SA parameter response frames, or an aggregated SA parameter response frame, to the client over the wireless connection. The client is further configured to select a target AP from the candidate APs based on the SA parameter response frame(s), and to exchange data with the target AP after roaming.

[0016] In accordance with the present disclosure, the client need no longer successively and passively scan multiple channels, one after another, to learn which DFS channels are valid for transmission, i.e., not carrying radar signals. Instead, an aggregated SA channel information request frame is constructed and sent to the SA handler that, in turn, sends an individual SA channel information request message to each AP, receives an individual SA channel information response message from each AP, and forwards individual SA channel response frames based on the individual SA channel information response messages to the client. In addition or separately, an aggregated SA IE request frame, and preferably a single such request frame, is constructed and sent to the SA handler that, in turn, sends an individual SA IE request message to each AP, receives an individual SA IE response message from each AP, constructs an aggregated SA IE response frame from the received individual SA IE response messages, and sends the aggregated SA IE response frame to the client. The aforementioned time taken to learn which DFS channels are valid for transmission, i.e., not carrying radar signals, is greatly reduced, and the client can now readily perform roaming in a rapid, reliable, efficient, high quality, and consistent manner.

[0017] Turning now to FIG. 1 of the drawings, an arrangement in accordance with this disclosure includes a wired or wireless, distribution system (DS) having a plurality of interconnected access points (APs), which are separately identified as API, AP2, AP3, ... , APN, where N is any whole number; a mobile, wireless communications client currently exchanging data with one (e.g., API) of the APs, hereinafter sometimes referred to as the current AP; and a real or virtual controller interconnected to all the APs. The client is shown in FIG. 1 as a tablet, but it will be understood that other supplicant devices, such as a smartphone, a laptop or portable computer, a personal digital assistant, a wearable communications device, or a handheld and/or vehicular radio, could also be employed. As shown, the client in FIG. 1 is currently exchanging data with the current AP, and wishes to roam along the illustrated roaming direction to another (e.g., AP3) of the APs, hereinafter sometimes referred to as the target AP, in order to exchange data with the target AP after roaming. Each AP is a wireless router and acts as a bridge to the DS.

[0018] A connection and time sequence diagram is depicted in FIG. 2 to explain the operation of the arrangement of FIG. 1. The client, the current AP, and the target AP are arranged along the top of FIG. 2, and the various functions performed by each are set forth as one proceeds down the figure towards the bottom of FIG. 2. Thus, in accordance with the IEEE 802.11 standard, the client is currently exchanging data with the current AP, because the client had already sent an authentication request frame to the current AP, then had already received an authentication response frame from the current AP, then had already sent an association request frame to the current AP, and then had already received an association response frame from the current AP. In addition, if it is a secure wireless network, keys in accordance with the IEEE 802. IX standard were derived and exchanged between the client and the current AP, thereby enabling the data to be securely exchanged.

[0019] In accordance with the present disclosure, before the client decides to roam away from the current AP, the following steps are performed. First, the client discovers candidate APs that are available on DFS channels for roaming from among the other APs. This can be accomplished by having the client request a neighbor list of the other APs that neighbor the current AP in accordance with the IEEE 802.11k standard, or by having the client scan the other APs by passively listening for beacons from the other APs, or for probe responses from the other APs resulting from an active scan.

[0020] Next, the client combines basic service set identifier (BSSID) information, i.e., the AP address, from the candidate APs to construct an aggregated scan assist (SA) channel information request frame, and sends the aggregated SA channel information request frame to an SA handler over a wireless connection. The SA handler receives the aggregated SA channel information request frame from the client, sends an individual SA channel information request message based on the aggregated SA channel information request frame to each candidate AP over the DS, receives an individual SA channel information response message from each candidate AP over the DS, and forwards an individual SA channel information response frame based on the individual SA channel information response message from each candidate AP to the client over the wireless connection. The SA handler depicted in FIG. 2 is not necessarily a separate device, and is preferably located in the current AP, as depicted in FIG. 1. The SA handler, however, could also be located elsewhere, for example, in any of the other APs, or in a real or virtual controller in the DS, or in the DS itself, or in the cloud.

[0021] As described above, a plurality of the channels are dynamic frequency selection (DFS) channels designated to carry radar signals of higher priority than the data exchanged by the client. By way of example, API may be exchanging data with the client over channel 52, and AP2 may be on DFS channel 56, and AP3 may be on DFS channel 60. The client determines the validity of DFS channels 56, 60 for transmission which, in turn, confirms the presence or absence of radar signals on the DFS channels 56, 60 based on the received individual SA channel information response frames. If there are no radar signals on DFS channels 56, 60, then the client actively scans those DFS channels by sending probe request frames to the APs on the DFS channels 56, 60, by receiving probe response frames from the APs on the DFS channels 56, 60, and selects which of the APs on the DFS channels 56, 60 is best suited to roam to. This selection can be based on various factors. For example, if the client determines that AP3 on channel 60 has the highest received signal strength indication (RSSI) from the APs on DFS channels 56, 60, then the client will select AP3 as the target AP, and exchange data with the target AP over DFS channel 60. The exchange of data with the target AP occurs after a roam and key derivation in the case of a secured network (see FIG. 1). If a radar signal is detected on one of the DFS channels 56, 60, as indicated by the channel information in a received individual SA channel information response frame, then the client will not select the AP on that channel.

[0022] The aggregated SA channel information request frame to the SA handler may have included a request for unsolicited periodic channel information responses from the other APs. In this case, the SA handler forwards the periodic individual SA channel information response frames to the client over the wireless connection in response to the request. An active scan is permitted on a DFS channel carrying no radar signal for a period of T seconds, typically 10 seconds. The individual SA channel information response frames may be sent every "M" seconds, where M < T.

[0023] If the aggregated SA channel request frame to the SA handler did not include such a request for unsolicited periodic channel responses, then the client may itself send the aggregated SA channel request frame periodically to the SA handler over the wireless connection. In that case, the SA handler forwards the individual SA channel response frames over the wireless connection to the client in response to each aggregated SA channel request frame sent by the client.

[0024] FIG. 3 depicts a connection and time sequence diagram analogous to that shown in FIG. 2, except the scan and roam parameters to be retrieved is not channel information, but information elements (IEs) of the other APs. The IEs are descriptive information about the APs, and, for example, may include the service set identity (SSID), the supported data rates, one or more physical (PHY) parameter sets, an optional contention-free parameter set, an optional independent basic service set (IBSS) parameter set, and an optional traffic indication map. The client uses BSS information from the candidate APs to construct an aggregated SA IE request frame, and sends the aggregated SA IE request frame, and preferably a single such frame, to the SA handler over a wireless connection. The SA handler receives the aggregated SA IE request frame from the client, sends an individual SA IE request message based on the aggregated SA IE request frame to each candidate AP over the DS, receives an individual SA IE response message from each candidate AP over the DS, constructs an aggregated SA IE response frame from the individual SA IE response messages, and sends the aggregated SA IE response frame, and preferably a single such frame, to the client over the wireless connection.

[0025] The above steps have all been performed prior to the client deciding to roam. The client selects which of the other candidate APs is best suited to roam to. This selection can be based on various factors. For example, if the client determines that AP3 has the highest received signal strength indication (RSSI) from among all of the candidate APs, then the client will select AP3 as the target AP. As another example, this selection can be based on the aggregated SA IE response frame.

[0026] Each of the aggregated request and response frames described above is formatted in one or more packets with multiple data fields, at least one of the fields being designated as an SA parameter aggregate field containing information about all the candidate APs (AP2, AP3, ... , APN). The information includes, among other things, the address and parameters of each one of the candidate APs (AP2, AP3, ... , APN).

[0027] In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. For example, the retrieval of the channel information and the retrieval of the IE information can be performed independently of each other, or simultaneously. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings. [0028] The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

[0029] Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," "has," "having," "includes," "including," "contains," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, contains a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises ... a," "has ... a," "includes ... a," or "contains ... a," does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, or contains the element. The terms "a" and "an" are defined as one or more unless explicitly stated otherwise herein. The terms "substantially," "essentially," "approximately," "about," or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1%, and in another embodiment within 0.5%. The term "coupled" as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0030] It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or "processing devices") such as microprocessors, digital signal processors, customized processors, and field programmable gate arrays (FPGAs), and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and/or apparatus described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.

[0031] Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory) and a Flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein, will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

[0032] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

CLAIMS:

1. In a distribution system (DS) having a mobile client wanting to roam away from a current access point (AP) with which the client is currently exchanging data, a method of enhancing scan and roam performance of the client by retrieving scan and roam parameters from other APs interconnected with the current AP over the DS, the method comprising:

the client discovering candidate APs that are available for roaming from among the other APs;

the client combining information from the candidate APs to construct an aggregated scan assist (SA) parameter request frame, and sending the aggregated SA parameter request frame to an SA handler over a wireless connection;

the SA handler sending an individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, receiving an individual SA parameter response message from each candidate AP over the DS, and forwarding an SA parameter response frame to the client over the wireless connection; and

the client selecting a target AP from the candidate APs based on the SA parameter response frame, and exchanging data with the target AP after roaming.

2. The method of claim 1, wherein the discovering of the candidate APs is performed by the client requesting a neighbor list of the candidate APs that neighbor the current AP.

3. The method of claim 1, wherein the discovering of the candidate APs is performed by the client scanning the DS for the candidate APs.

4. The method of claim 1, and formatting the aggregated SA parameter request frame with multiple data fields, at least one the fields containing information about all the candidate APs.

5. The method of claim 1, and locating the SA handler in one of the current AP, one of the other APs, a controller of the DS, and the DS.

6. The method of claim 1, wherein the scan and roam parameters include channel information of the other APs, a plurality of which are dynamic frequency selection (DFS) channels designated to carry radar signals of higher priority than the data exchanged by the client; wherein the SA handler forwards individual SA parameter response frames based on the individual SA parameter response messages to the client; and wherein the client determines the absence of radar signals on the DFS channels based on the individual SA parameter response frames, sends probe request frames on the DFS channels having no radar signals, receives probe response frames on the DFS channels having no radar signals, roams, and exchanges data with the target AP over one of the DFS channels having no radar signals.

7. The method of claim 6, wherein the client itself sends the aggregated SA parameter request frame periodically to the SA handler over the wireless connection, and wherein the SA handler forwards the individual SA parameter response frames over the wireless connection to the client in response to each aggregated SA parameter request frame sent by the client.

8. The method of claim 6, wherein the client sends the aggregated SA parameter request frame to the SA handler over the wireless connection with a request for unsolicited periodic parameter response messages from the other APs, and wherein the SA handler forwards the periodic individual SA parameter response frames to the client over the wireless connection in response to the request.

9. The method of claim 1, wherein the roam and scan parameters include information elements (IEs) of the other APs; wherein the SA handler combines the individual SA parameter response messages to construct an aggregated SA parameter response frame, and sends the aggregated SA parameter response frame to the client over the wireless connection.

10. An arrangement for enhancing scan and roam performance by retrieving scan and roam parameters, comprising:

a distribution system (DS) having a plurality of interconnected access points (APs);

a mobile client currently exchanging data with one of the APs (current AP) and wanting to roam away from the current AP, the client being configured to discover candidate APs that are available for roaming from among others of the APs, and to combine information from the candidate APs to construct an aggregated scan assist (SA) parameter request frame; an SA handler for receiving the aggregated SA parameter request frame sent by the client over a wireless connection, the SA handler being configured to send an individual SA parameter request message based on the aggregated SA parameter request frame to each candidate AP over the DS, to receive an individual SA parameter response message from each candidate AP over the DS, and to forward an SA parameter response frame to the client over the wireless connection; and

the client being further configured to select a target AP from the candidate APs based on the individual SA parameter response messages, and to exchange data with the target AP after roaming.

11. The arrangement of claim 10, wherein the client is configured to discover the candidate APs by the client requesting a neighbor list of the candidate APs that neighbor the current AP.

12. The arrangement of claim 10, wherein the client is configured to discover the candidate APs by the client scanning the DS for the candidate APs.

13. The arrangement of claim 10, wherein the aggregated SA parameter request frame is formatted with multiple data fields, at least one the fields containing information about all the candidate APs.

14. The arrangement of claim 10, wherein the SA handler is located in one of the current AP, one of the other APs, a controller of the DS, and the DS.

15. The arrangement of claim 10, wherein the scan and roam parameters include channel information of the other APs, a plurality of which are dynamic frequency selection (DFS) channels designated to carry radar signals of higher priority than the data exchanged by the client; wherein the SA handler is configured to forward individual SA parameter response frames based on the individual SA parameter response messages to the client; and wherein the client is configured to determine the absence of radar signals on the DFS channels based on the individual SA parameter response frames, to send probe request frames on the DFS channels having no radar signals, to receive probe response frames on the DFS channels having no radar signals, to roam, and to exchange data with the target AP over one of the DFS channels having no radar signals.

16. The arrangement of claim 15, wherein the client is configured to periodically send the aggregated SA parameter request frame to the SA handler over the wireless connection, and wherein the SA handler is configured to forward the individual SA parameter response frames over the wireless connection in response to each aggregated SA parameter request frame sent by the client.

17. The arrangement of claim 15, wherein the client is configured to send the aggregated SA parameter request frame to the SA handler over the wireless connection with a request for unsolicited periodic parameter response messages from the other APs, and wherein the SA handler is configured to forward the periodic individual SA parameter response frames over the wireless connection in response to the request.

18. The arrangement of claim 10, wherein the scan and roam parameters include information elements (IEs) of the other APs; wherein the SA handler is configured to combine the individual SA parameter response messages to construct an aggregated SA parameter response frame, and to send the aggregated SA parameter response frame to the client over the wireless connection.