This application makes reference to the following commonly owned U.S. patent applications and patents, which are incorporated herein by reference in their entirety for all purposes:
U.S. patent application Ser. No. 10/155,938 in the name of Patrice R. Calhoun, Robert B. O'Hara, Jr. and Robert J. Friday, entitled “Method and System for Hierarchical Processing of Protocol Information in a Wireless LAN;”
U.S. patent application Ser. No. 10/407,357 in the name of Patrice R. Calhoun, Robert B. O'Hara, Jr. and Robert J. Friday, entitled “Method and System for Hierarchical Processing of Protocol Information in a Wireless LAN;”
U.S. patent application Ser. No. 10/407,370 in the name of Paul Dietrich, Robert B. O'Hara, Jr. and David A. Frascone, entitled “Wireless Network System Including Rogue Access Point Detection;”
U.S. patent application Ser. No. 10/409,246 in the name of Robert J. Friday and Alexander H. Hills, entitled “Method And System For Dynamically Assigning Network Resources In Wireless Network;” and
U.S. patent application Ser. No. 10/447,735 in the name of Robert B. O'Hara, Jr., Robert J. Friday, Patrice R. Calhoun and Paul Dietrich, entitled “Wireless Network Infrastructure including Wireless Discovery and Communication Mechanism.”
The present invention relates to wireless computer networks and, more particularly, to methods, apparatuses and systems enabling a directed association mechanism in wireless computer network environments.
Wireless computer network environments generally comprise a plurality of wireless access points that, when operating in the infrastructure mode, bridge wireless traffic between a wired computer network and the wireless clients that associate with the access points. A wireless Local Area Network (WLAN) is a wireless communication system with radios having relatively high throughput and short coverage ranges. Many wireless LANs are based on iterations of the IEEE 802.11 standard. When a wireless client initializes or moves into an entirely new coverage area, according to the 802.11 standard, it transmits probe requests to locate access points to which it may associate to establish a wireless connection. Often, the wireless client may detect multiple access points. The 802.11 standard, however, generally leaves it to the wireless client to decide with which access point to associate. That is, a wireless client scans the available channels in the region and listens to the Beacon or Probe Response Frames transmitted by access points in that region. The wireless client stores the RSSI (Received Signal Strength Indicator) of the Beacon or Probe Response Frames and other relevant information, such as BSSID, encryption (on/off), etc. After finishing the scanning procedure, the wireless client generally selects the access point with the maximum RSSI, given that the selected access point satisfies other requirements (typically, BSSID, and WEP encryption) as well. The wireless client leaves or disassociates with the access point when the RSSI falls under a predefined threshold, such as when the user walks away from the coverage area of the access point. This association process, however, often results in uneven loads across access points, where many wireless clients are connected to only a few access points in a wireless environment, while other access points may remain idle or lightly loaded. That is, as discussed above, the wireless clients make association decisions based on what is best for the wireless client as opposed to what is best for the overall efficiency and performance of the wireless network environment.
As discussed above, the wireless client, therefore, acts only with regard to its own self-interest and, thus, will generally associate with the access point based on received signal strength without regard to the load on the access point (e.g., number of wireless clients, data throughput, etc.). The access point largely has no influence over the decision process at the wireless client except to deny the association requested by the wireless client. Denying the association, generally spurs the wireless client to repeat the process of discovering access points by transmitting probe requests and scanning the air for Beacon and Probe Response Frames. Many wireless clients, however, simply select the same access point as the logic the implement does not take account of previous association denials. Accordingly, this circumstance renders load balancing and other resource management tasks more problematic. In addition, even with wireless clients that take account of previous association denials, the discovery of access points by wireless client devices and having to repeat the process when associations are denied takes time, adversely affecting the operational efficiency of the network and degrading the wireless client user's experience.
The prior art for resource management in the area of wireless LANs addresses the problem of allocation of network resources by placing proprietary and non-standard intelligence in both the client and the access point in order to allow the client to make association decisions with information received from the radio access point. In order to be effective, it must limit the network to a homogenous client and infrastructure base, which typically is associated with proprietary software.
One example of such an infrastructure is found in I. Papanikos and M. Logothetis, A Study on Dynamic Load Balance for IEEE 802.11b Wireless LAN, cited as www.wcl.ee.upatras.gr/m-logo/papers/IEEE80211-P41.pdf, (7 pp.) and noted as posted as of at least 12 Nov. 2002. This reference describes an algorithm in which the client makes an association decision based on: the number of clients associated with the radio access point, the received signal strength indication (RSSI) value of the Probe Request received from the client by the radio access point, and the mean RSSI value of the signals received by the radio access point from other clients associated with the radio access point. The paper concludes that the algorithm does not perform well in the presence of hidden nodes and/or highly asymmetric traffic. Despite taking account of loading conditions, the association decisions are still allocated to the wireless client, which assesses a plurality of weighted factors to select an access point with which to associate. The association selection, however, may nevertheless not be appropriate based on the current loading conditions of the network. The selected access point in this instance will then deny the association request, causing the wireless client to repeat the scanning process.
In light of the foregoing, a need in the art for methods, apparatuses and systems that facilitate load balancing and other tasks associated with wireless network environments. A need further exists for a mechanism that reduces the number of association attempts in wireless computer networks. A need further exists for a mechanism that facilitates roaming in wireless network environments. Embodiments of the present invention substantially fulfill these needs.
The present invention provides methods, apparatuses and systems enabling a directed association mechanism in wireless computer network environments. In certain embodiments, the directed association functionality described herein can be used in a variety of contexts, such as directing wireless clients to associate with a particular access element or subset of access elements in a wireless network environment. In certain embodiments, the present invention can also be used to increase the efficiency of handing off wireless clients between access elements. As discussed below, the directed association mechanism, in one embodiment, increases the efficiency of establishing wireless connections between wireless clients and access points or elements in a wireless network system.
A. Network Environment Overview
For didactic purposes an embodiment of the present invention is described as operating in a WLAN environment as disclosed in U.S. application Ser. Nos. 10/155,938 and 10/407,357 incorporated by reference herein. As discussed below, however, the present invention can be implemented according to a vast array of embodiments, and can be applied to a variety of WLAN architectures.
The access elements 12-15 are coupled via communication means using a wireless local area network (WLAN) protocol (e.g., IEEE 802.11a or 802.11b, etc.) to the client remote elements 16, 18, 20, 22. The communications means 28, 30 between the access elements 12, 14 and the central control element 24 is typically an Ethernet network, but it could be anything else which is appropriate to the environment. As described in U.S. application Ser. Nos. 10/155,938 and 10/407,357, the access elements 12, 14 and the central control element 24 tunnel network traffic associated with corresponding remote client elements 16, 18; 20, 22 via direct access lines 28 and 30, respectively, or a LAN. Central control element 24 is also operative to bridge the network traffic between the remote client elements 16, 18; 20, 22 transmitted through the tunnel with corresponding access elements 12, 14.
In one embodiment, the access elements, such as access elements 12, 14, include functionality allowing for detection of the strength of the signal received from client remote elements and/or other access elements. For example, the IEEE 802.11 standard defines a mechanism by which RF energy is measured by the circuitry (e.g., chip set) on a wireless network adapter or interface card. The 802.11 protocol specifies an optional parameter, the receive signal strength indicator (RSSI). This parameter is a measure by the PHY layer of the energy observed at the antenna used to receive the current packet or frame. RSSI is measured between the beginning of the start frame delimiter (SFD) and the end of the PLCP header error check (HEC). This numeric value is typically an integer with an allowable range of 0-255 (a 1-byte value). Typically, 802.11 chip set vendors have chosen not to actually measure 256 different signal levels. Accordingly, each vendor's 802.11-compliant adapter has a specific maximum RSSI value (“RSSI_Max”). Therefore, the RF energy level reported by a particular vendor's wireless network adapter will range between 0 and RSSI_Max. Resolving a given RSSI value reported by a given vendor's chip set to an actual power value (dBm) can be accomplished by reference to a conversion table. In addition, some wireless networking chip sets actually report received signal strength in dBm units, rather than or in addition to RSSI. Other attributes of the signal can also be used in combination with received signal strength or as an alternative. Again, many chip sets include functionality and corresponding APIs to allow for a determination of signal-to-noise ratios (SNRs) associated with packets received from client remote elements. In one embodiment, access elements 12, 14 include the detected signal strength and/or SNR value associated with a packet in the encapsulating headers used to tunnel the wireless packets to central control element 24. As discussed below, the remote client elements, in one embodiment, include signal attribute detection functionality as well.
As described in the above-identified patent applications, central control element 24 operates to perform data link layer management functions, such as authentication and association on behalf of access elements 12, 14. For example, the central control element 24 provides processing to dynamically configure a wireless Local Area Network of a system according to the invention while the access elements 12, 14 provide the acknowledgment of communications with the client remote elements 16, 18, 20, 22. The central control element 24 may for example process the wireless LAN management messages passed on from the client remote elements 16, 18; 20, 22 via the access elements 12, 14, such as authentication requests and authorization requests, whereas the access elements 12, 14 provide immediate acknowledgment of the communication of those messages without conventional processing thereof. Similarly, the central control element 24 may for example process physical layer information. Still further, the central control element 24 may for example process information collected at the access elements 12, 14 on channel characteristic, propagation, and interference or noise. Central control elements 25, 26 and associated access elements 13, 15 operate in a similar or identical manner. Other system architectures are possible. For example, U.S. application Ser. No. 10/407,357 discloses a system architecture where the access elements, such as access elements 12-15, are directly connected to LAN segment 10.
Other system architectures are also possible. For example, in another embodiment, the directed association functionality described herein can be implemented within the context of a single, autonomous access point, which can be configured to communicate with other access points and/or a central management platform 21 via SNMP, HTTP, or other protocols. See
B. Operation
As the following provides, the directed association functionality described herein can be used in a variety of contexts, such as directing wireless clients to associate with a desired access element or subset of access elements in a wireless network environment. In certain embodiments, the present invention can also be used to increase the efficiency of handing off wireless clients between access elements. These and other objectives will become apparent from the exemplary embodiment described below.
B.1. Directed Association
B.1.a. Wireless Client Functionality
As
After selection of an access element, the wireless client transmits an association request (208) to the selected access element. In one embodiment, the wireless client includes a list of access elements (identified, in one embodiment, by MAC address and BSSID) detected during the scan. In one embodiment, the list is embodied in a table which also includes the RSSI values detected during receipt of either Beacon or Probe Response Frames. In one embodiment, the list or table of access elements is ordered according to a preference computed by the wireless client. In 802.11 environments, the wireless client may first transmit an authentication request and receive an authentication response (not shown in
If the access element responds, the wireless client determines whether the association response includes an acceptance notification or a rejection notification (212). If the access element accepts the requested association, the wireless client establishes or completes the wireless connection (214) according to the applicable wireless protocol. If the access element rejects the requested association, the wireless client scans the association response to determine whether it identifies alternative access elements with which to associate (see below). If so, the wireless client selects from the identified access element(s) and transmits an association request to the selected access element (218). As discussed in more detail below, generally speaking the newly requested association should be accepted as the list of alternative access elements was computed by the wireless network system as being available to the wireless client.
B.1.b. Access Element/Central Control Element Functionality
As
As
In yet other embodiments, the list of allowable access elements may be computed with respect to geographic/location considerations, as well as detected radio-frequency connectivity or overlap among access elements. For example, as disclosed in U.S. application Ser. No. 10/447,735, the access elements can be configured to exchange so-called neighbor messages to allow the central control elements or a central management platform to map the RF connectivity of the access elements. The set of allowable access elements can be reduced to the set of access elements having RF connectivity within a given signal strength threshold to the access element initially selected by the wireless client. In another embodiment, the central control elements can be configured with geographic or other location information relating to the access elements and select or further filter the set of allowable access elements based on geographic proximity to the access element initially selected by the wireless client.
In one embodiment, if the current access element 12 is included in the set of allowable access elements (108), then the central control element 24 sets the notification value in the association response to “accept” (110) and transmits the association response (118). Optionally, the association response may also include the set of other allowable access elements. However, if the current access element is not in the allowable set, the central control element 24 sets the notification value in the association response to “reject” (112). The central control element 24 then compares the set of access elements detected by (or detecting) the wireless client, see above, to the computed set of allowable access elements. If there is any overlap between the two sets, the central control element 24 appends the list of common access elements (in one embodiment, identified by MAC address) to the association response (116) and transmits the association response to the wireless client (118). As discussed above, the wireless client can then use this list of access elements in subsequent association attempts, being, in one embodiment, virtually guaranteed (assuming the association request is transmitted in a sufficiently small period of time from the response) that an association request directed to an access element on this list will be accepted. As one skilled in the art will recognize, this protocol greatly reduces the time inherent in having to repeat the scan for access elements only to attempt to associate with the same access element, or another access element, that will deny the association.
In one embodiment, the table or other data structure included in the association response can include a variety of information. In one embodiment, the table can include the access element identifier, such as MAC address, and the BSSID of the access element. The table can also include other parameters, such as the operating channel of the access element, as well as operational parameters and characteristics, such as current load, and duty cycle. In one embodiment, the association response can also include other information, such as the RSSI values of the Probe Requests detected at each access element, to allow the wireless client to base its selection, at least in part, on this metric.
B.2. Directed Handoff
Once the wireless client is associated, the wireless network system, in one embodiment, can operate to facilitate handoffs of the wireless client between different access elements. For example, assume for didactic purposes that the data throughput load at access element 12 has risen above a threshold level, causing central control element 24 to decide that at least one currently-associated wireless client must be handed off to another access element.
The invention has been explained with reference to specific embodiments. Other embodiments will be evident to those of ordinary skill in the art. For example, the present invention can also be applied to WLAN architectures beyond the hierarchical WLAN architecture described above. For example, in another embodiment, the directed association functionality described herein can be implemented within the context of a single, autonomous access point, which can be configured to exchange necessary information with other similarly configured access points and communicate with such access points over the wired network to coordinate configuration and other management tasks. See
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