Abstract:
A system and method for providing a seamless transition between access points for mobile devices. The method comprises associating a unique identifier for a plurality of mobile stations with a unique identifier for a first network in an acknowledgment table, then, upon receiving a frame from a mobile station, acknowledging the reception of the frame if the frame includes the unique identifier for the mobile station and the unique identifier for the network. The transfer of operation between access points is effectuated through the use of control circuitry which transfers portions of the contents of the acknowledgement table between various access points. This has the effect that the mobile stations does not sense a change in access points and thus the roaming from a first access point to a second access point is seamless.

Description:
INCORPORATED DISCLOSURES AND RELATED APPLICATIONS 
     This application claims the priority of, and hereby includes by reference as if fully set forth herein, the following:
         U.S. Provisional Patent Application 61/095,578, filed Sep. 9, 2008, in the name of Vaduvur BHARGHAVAN and Berend DUNSBERGEN, titled “Seamless Roaming in Wireless Networks, assigned to the same assignee,   U.S. patent application Ser. No. 11/715,287, filed Mar. 7, 2007, in the name of Vaduvur BHARGHAVAN, Sung-Wook HAN, Joseph EPSTEIN, Berend DUNSBERGEN, and Saravanan BALASUBRAMANIAN, titled “Seamless Mobility in Wireless Networks”, assigned to the same assignee,   which itself claims the priority of, and hereby incorporates by reference as if fully set forth herein, the following: U.S. patent application Ser. No. 11/298,864, filed Dec. 9, 2005, in the name of Vaduvur BHARGHAVAN, Sung-Wook HAN, Joseph EPSTEIN, Berend DUNSBERGEN, and Saravanan BALASUBRAMANIAN, titled “Seamless Mobility in Wireless Networks”, and assigned to the same assignee,   which itself claims the priority of, and hereby incorporates by reference as if fully set forth herein, the following: U.S. patent application Ser. No. 11/294,673, filed Dec. 5, 2005, in the name of Rajendran VENUGOPALACHARY, Senthil PALANISAMY, Srinith SARANG, and Vaduvur BHARGHAVAN, titled “Omni-Directional Antenna Supporting Simultaneous Transmission and Reception of Multiple Radios with Narrow Frequency Separation”, and assigned to the same assignee.       

     These documents are sometimes referred to herein as the “Incorporated Disclosure” or the “Incorporated Disclosures”. 
    
    
     In wireless communication, devices send and receive messages without necessarily being physically coupled therefor. Wireless devices sometimes include location sensors (such as those using GPS), portable computers, mobile telephones, and the like. Portable computers with wireless communication capability sometimes are coupled to a computer network, such as the Internet or the World Wide Web. The IEEE 802.11 standards (including IEEE standard 802.11a, IEEE standard 802.11b, IEEE standard 802.11g, and IEEE standard 802.11n) include techniques for coupling wireless devices to computer communication networks. In the IEEE 802.11 standards, wireless devices seek out and select “access points”, also called “AP&#39;s”. Each wireless device associates itself with a particular AP, with which it communicates. Each wireless device, such as a mobile station, also called an “STA” (which might be moving), determines from time to time whether it has good communication with its associated AP, and whether it would have better communication with a different AP. 
     Access points exhibit a known deficiency when an STA moves beyond the effective range of an AP, because the STA needs to re-establish communication with a new AP, a process called “handoff”. Handoff problems include loss of signal and decrease in QoS (Quality of Service). For applications requiring high QoS, such as digitally transmitting audio information, the latency time of the handoff can be uncomfortably perceptible to a human listener. 
     SUMMARY 
     Techniques, including apparatuses and methods for seamless transitions between AP&#39;s include associating a station UID (unique identifier) for a set of mobile stations, with a network UID for a 1 st  network in an acknowledgment table. Upon receiving a frame from a mobile station in that set of mobile stations, reception of the frame is acknowledged only if the frame includes both the station UID for the mobile station and the network UID for the network. This has the effect that mobile stations might be associated with selected networks (and selected AP&#39;s), without troubling those AP&#39;s or their control hardware or software. 
     Transfer of a station&#39;s operation between AP&#39;s (i.e., handoff) is performed by transferring one or more portions of acknowledgment tables among AP&#39;s. This has the effect that AP&#39;s collectively know which AP is associated with that mobile station, and collectively respond to that mobile station only by its associated AP. This has the effect that when the AP&#39;s collectively (e.g., in response to a controller as described in the Incorporated Disclosures) determine that the mobile station should be transferred from a 1 st  AP to a 2 nd  AP, the mobile station does not sense a change in AP&#39;s, with the effect that any transfer from a 1 st  AP to a 2 nd  AP is substantially seamless to users of the mobile station. 
     This has the effect that AP&#39;s (or their controller, as described in the Incorporated Disclosures), determine to which AP each mobile station is associated, rather than the reverse (as generally specified by the IEEE standard protocols). In general, AP&#39;s and their controller are in a better position to determine to which AP a mobile station should be associated. Moreover, there is no particular requirement for a particular mobile station to undergo a time-consuming process of handoff when that mobile station should, from time to time, be associated with a different AP. This has the effect that the mobile station can be transferred between a 1 st  AP and a 2 nd  AP without troubling the mobile station, without even letting the mobile station know that the transfer has taken place, and without substantial latency in making the transfer. 
     DETAILED DESCRIPTION 
     Generality of Invention 
     This application should be read in its most general possible form. For example and without limitation:
         References to specific techniques include alternative and more general techniques, especially when discussing new aspects of the technologies, or how the invention might be made or used.   References to “preferred” techniques generally mean that the inventors contemplate using those techniques in a suitable context, for example and without limitation, a commercial context, and think they are best for that contemplated context. This explicitly does not exclude other and further techniques for making or using the invention, and does not mean that the described techniques are necessarily essential or that they would be preferred in all contexts.   References to contemplated causes and effects for some implementations do not preclude other causes or effects that might occur in other implementations.   References to reasons for using particular techniques do not preclude other reasons or other techniques, even if completely contrary, where circumstances would indicate that the stated reasons or techniques are not as applicable.   References to particular examples of techniques by which the invention might be made, used, or otherwise employed, do not preclude other examples or other techniques, even if completely contrary. After reading this application, those skilled in the art will recognize many other variations which are possible, which remain within the content, scope and spirit of the invention, and which would not require undue experimentation or new invention.       

     DEFINITIONS 
     This application should be read with these definitions in mind. These definitions are intended to show the most general form of the invention, and not to be restrictive in any way:
         The phrase “access point”, the term “AP”, and the like, generally refer to devices capable of wireless communication with wireless devices and capable of either wired or wireless communication with other devices. The term “AP&#39;s”, and the like, generally refers to a set of one or more such devices. For example, AP&#39;s might communicate with external devices using a L2/L3 network. However, in the context of the invention, there is no particular requirement that AP&#39;s have an actual wired communication link; AP&#39;s might communicate entirely wirelessly themselves.   The phrases “incoming message”, “received frame”, and the like, generally refer to a message packet or message frame sent by a wireless device or wireless station to one or more AP&#39;s, and received at a particular AP. Received frames might be sent by a wireless station to one or more AP&#39;s using one or more of the IEEE 802.11 wireless communication standards, some similar one or more standards, or some other one or more standards. The incoming message may be a unicast frame (i.e., intended for a single AP) or a multicast frame (i.e., intended for a set of, possibly multiple, AP&#39;s).   The phrases “outgoing message” and “transmit frame”, and the like, generally refer to a message packet or message frame being sent to one or more wireless devices or stations from an AP. Transmit frames might be sent from an AP using one or more of the IEEE 802.11 wireless communication standards, some similar one or more standards, or some other one or more standards. The incoming message may be a unicast frame (i.e., intended for a single AP) or a multicast frame (i.e., intended for a set of, possibly multiple, AP&#39;s).   The phrase “wireless communication”, and the like, generally refers to radio frequency or other electromagnetic communication. Wireless communication might make use of a wireless communication standard such as one or more of IEEE standards 802.11a, 802.11b, 802.11g, or 802.11n, some similar one or more standards, or some other one or more standards. However, in the context of the invention, there is no particular requirement that wireless communication or a communication network must necessarily (1) use radio spectrum, (2) use electromagnetic communication, or even (3) be entirely confined to untethered communication coupling. For examples, wireless communication might use sonic waves, possibly including ultrasound, or wireless communication might make use of both wired and unwired communication paths.   The phrases “wireless device”, “wireless station”, “mobile station” and the like, (“STAs”) generally refer to devices capable of wireless communication with AP&#39;s. These devices need not be mobile, such as for example a desktop computer with wireless capability. Wireless communication might make use of a wireless communication standard such as one or more of IEEE standards 802.11a, 802.11b, 802.11g, or 802.11n, some similar one or more standards, or some other one or more standards. However, in the context of the invention, there is no particular requirement that one or more of these particular communication standards are used, e.g., the wireless communication might be conducted according to a standard other than an IEEE 802.11 standard, or even according to standard other than an IEEE standard entirely. Moreover, in the context of the invention, there is no particular requirement that all, or even a designated subset of, wireless devices use the same standard, or that such wireless devices even use inter-compatible communication standards.   Digital communications devices might operate using a multi-layer configuration, such as for example one including Application, Presentation, Session, Transport, Network, Data Link, and Physical layers. The term “layer”, and the like, generally refers to a collection of related functions that provides services to one or more layers above it and receives services from one or more layers below it in a designated ordering. For example, a layer that provides error-free communications across a network might provide a path useful to applications above it, while that layer that provides error-free communications across a network might make use of one or more lower layers to send and receive packets that make up the contents of the path.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a table illustrating an acknowledgment table (“ACK Table”) as might be found in a memory device of an access point, or in the control circuitry of a wireless Communications device (i.e., a mobile device), according to an embodiment. 
         FIG. 2  is a table illustrating the beginning of a typical frame format for use in the IEEE 802.11 communications protocol, according to an embodiment. 
         FIG. 3  is a block diagram illustrating access points sharing a BSSID for a mobile station, according to an embodiment. 
         FIG. 4  is a block diagram illustrating access points utilizing a per station BSSID, according to an embodiment. 
     
    
    
     ACK Table Operation 
     
       FIG. 1 
     
       FIG. 1  illustrates an acknowledgment table (“ACK Table”) as might be found in a memory device of an access point, or in the control circuitry of a wireless communications device (i.e., a mobile device). The ACK Table as shown provides for a data structure relating a station unique identifier such as a media access control (MAC) address of a mobile station to a basic service set identifier (BSSID), sometimes called herein a “network unique identifier” of a network. However, in the context of the invention, there is no particular requirement that these particular data items are used. Other, further, or distinct data elements might be used to match mobile stations with their associated networks. 
     A BSSID is used to identify one or more IEEE 802.11 wireless LAN&#39;s with which a mobile station attempts to communicate. An example of at least one vendor&#39;s implementation of an ACK Table implemented in a communications chip set is implemented and shown in Broadcom models 4342, 4322 and 4387. Other devices may have this same or a similar capability, whether or not from the same vendor. 
     In the ACK Table shown in the  FIG. 1 , a MAC address represents the physical address of a mobile device disposed for being connected to a network, generally expressed as a 48-bit hexadecimal number (i.e., 6 octets). Wireless networks are often included in a multi-layer configuration that allows for operation between hierarchies of systems. The MAC layer is generally a sublayer, as defined by the IEEE standard 802 protocols, of a networking layer. The MAC sublayer is responsible for delivering error-free data between two computers on the network. 
     Mobile stations are each associated with a station unique identifier, which is itself associated with a network unique identifier, the latter including a unique BSSID the mobile station might access, which is itself associated with one or more particular networks in a wireless communication system. This has the effect that the mobile station can access those particular networks, and no others. The mobile station&#39;s unique BSSID access ability might be moved from a 1 st  AP to a 2 nd  AP when reassigning the mobile station from the 1 st  AP to the 2 nd  AP. As only those AP&#39;s with the MAC address of the mobile station in their ACK Table will respond to the mobile station, the one or more AP&#39;s maintaining that unique BSSID are the only AP&#39;s that respond to message packets from the mobile station. While such AP&#39;s might be only one designated such AP at any particular time, in the context of the invention, there is no particular requirement for this restriction, and in fact, during transfer of a mobile station from a 1 st  AP to a 2 nd  AP, there will generally be at least some time during which the MAC address for that AP is present in the ACK Tables for each of the 1 st  AP and the 2 nd  AP. As the one or more AP&#39;s maintaining that unique BSSID are the only AP&#39;s that respond to message packets from that particular mobile station, this has the effect of limiting access by that particular mobile station to only networks available to those one or more AP&#39;s maintaining that unique BSSID. 
     
       FIG. 2 
     
       FIG. 2  shows the beginning of a typical frame format for use in the IEEE 802.11 communications protocol. Not all fields are necessarily present in every frame. Frame communication between the same devices may have different frame formats at different stages of the communication process. This may include changing frame formats between communication layers within a wireless communication device. 
     In operation, distinct receive frames might require differing responses or acknowledgments. For example and without limitation, a unicast MAC Protocol Data Unit (MPDU or MMPDU) receive frame generally requires, according to the IEEE 802 protocol standards, an ACK frame response. Other receive frames may require more efficient forms of acknowledgment such as BLOCK-ACK frames. Upon reception of a frame requiring an ACK, each AP receiving that frame will search its ACK Table for an entry where a MAC address matches a BSSID supported in the AP. Only if the received frame requires a response and a matching entry is found, will the AP respond with the appropriate response. The response type is based on the received frame. 
     Upon reception of a frame requiring an ACK, each AP receiving that frame will search its ACK Table for an entry where both the Address 1  matches the BSSID and the Address 2  matches the MAC address. Only if the received frame requires a response and a matching entry is found, will the AP respond with the appropriate response. The response type is in response to the received frame. 
     Shared BSSID 
     
       FIG. 3 
     
       FIG. 3  shows a functional block diagram of a sharing a BSSID. Mobile stations are configured to attempt to find available AP&#39;s for communication. Processors in the mobile stations evaluate factors for connections and make independent roaming decisions to make sure they are connected to the best AP. In preferred embodiments the mobile stations roam seamlessly across AP&#39;s because the roaming decisions are made by the infrastructure (APs and a controller). This has the effect that all handoffs between different APs are completely transparent to the mobile stations. 
     To effectuate seamless roaming, a 1 st  access point AP, contains an ACK Table as described above. The ACK Table contains both mobile station MAC addresses and BSSIDs and is coupled to one or more mobile stations. For the transition of STA 2  from AP 1  to AP 2 , both AP 1  and AP 2  support the same BSSID (BSSID 1 ). By creating a shared media environment with the same BSSID, both AP&#39;s can receive the same frame from STA 2 . However, through the operation of the ACK Table, only the AP that has a complete matching entry in the ACK Table will respond to the STA. Before the transition, only AP, has complete information for STA 2 . This has the effect that STA 2  transitions from AP 1  to AP 2  transparently because the STA does not sense that a different AP has taken over the communications link. Communication and coordination between the APs is preformed through the operation of the controller (not shown), which effects the proper ACK Table for each AP. 
     Per Station BSSID 
     
       FIG. 4 
     
       FIG. 4  shows a functional block diagram of using a per station BSSID. In the  FIG. 4  an access point AP 1  is constructed with an ACK Table having a MAC address for each mobile station and an associated BSSID for each mobile station. To effectuate seamless roaming, the BSSID from the 1 st  AP (AP 1 ) is transferred to the 2 nd  AP (AP 2 ) during the transition. The transfer is effectuated by a controller (not shown). Through the operation of the ACK Table, only the AP that has a complete matching entry in the ACK Table will respond to the STA. Before the transition, only AP 1  has complete information for STA 2 . During the transition, AP 2  receives complete ACK Table information relating to STA 2 . After the transition, only AP 2  has complete ACK Table information for STA 2 . This has the effect that STA 2  transitions from AP 1  to AP 2  transparently because the STA does not sense that a different AP has taken over the communications link. Communication and coordination between the AP&#39;s is performed through the operation of the controller, which effects the proper ACK Table for each AP. 
     Alternative Embodiments 
     The invention has applicability and generality to other aspects of wireless communication, and is not limited to wireless communication based upon IEEE 802.11 standards. After reading this application, those having skill in the art would recognize that the systems and methods disclosed herein my be effectuated using other techniques. For example and without limitation, the transmission time might be provided by the physical layer or data link layer to a higher level for determining the transmission time. 
     After reading this application, those skilled in the art would recognize that the scope and spirit of the invention include other and further embodiments beyond the specifics of those technologies disclosed herein, and that such other and further embodiments would not require undue experimentation or new invention.