Abstract:
Described is a system and method for optimizing wireless client communications. The system comprises a plurality of access points and a network management arrangement. The access points conduct wireless communications on a radio frequency channel with a plurality of wireless computing units. The access points are associated with a common destination identifier. The network management arrangement generates a list for each of the access points. The list includes source identifiers for selected ones of the wireless computing units. One of the access points only transmits a response signal in response to a received signal that includes a received signal source identifier matching one of the source identifiers on the list of the one access point.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a system and method for optimized wireless client communication. 
       BACKGROUND 
       [0002]    A conventional wireless network includes one or more access points (“APs”) allowing a user of a mobile unit (“MU”) to move freely within the network while maintaining a connection thereto. As the MU moves within the network, it may cease communicating with a first AP and begin communicating with a second AP, which is commonly referred to as a “roam.” To initiate communication with the second AP, the MU re-executes a roam procedure which was previously executed with the first AP. The roam procedure includes association and authentication of the MU by the second AP, and typically requires approximately 200 milliseconds to 3 seconds to complete. Thus, roaming between APs may cause a delay in the MU&#39;s communication on the network. For latency-sensitive applications (e.g., Voice over Internet Protocol (“VoIP”) calls), the delay may result in a termination of the connection of the MU to the network. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention generally relates to a system and method for optimized wireless client communication. The system comprises a plurality of access points and a network management arrangement. The access points conduct wireless communications on a radio frequency channel with a plurality of wireless computing units. The access points are associated with a common destination identifier. The network management arrangement generates a list for each of the access points. The list includes source identifiers for selected ones of the wireless computing units. One of the access points only transmits a response signal in response to a received signal that includes a received signal source identifier matching one of the source identifiers on the list of the one access point. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  shows an exemplary embodiment of a system according to the present invention; 
           [0005]      FIG. 2  shows an exemplary embodiment of a method according to the present invention; and 
           [0006]      FIG. 3  shows an exemplary embodiment of another method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention describes a system and a method for optimized wireless client communication. In the exemplary embodiment, the system includes multiple access points (“APs”) which are configured to utilize one basic service set identifier (“BSSid”) simulating a single AP. Thus, a mobile unit (“MU”) may travel about the WLAN and maintain a seamless wireless connection to a wireless network without suffering a delay associated with roaming. Although the exemplary embodiments of the present invention are described with reference to an IEEE 802.11 wireless network, those of skill in the art will understand that the present invention may be implemented in other types of network protocols and architectures. 
         [0008]      FIG. 1  shows an exemplary embodiment of a system  1  according to the present invention. The system  1  includes a network management arrangement (“NMA”)  60 , which is wired/wirelessly coupled to at least one AP (e.g., APs  10 ,  20 ,  30 , and  40 ). The system  1  may further comprise a server  70  and a database  75  coupled to the NMA  60  over a communications network  65 . The NMA  60  may be a switch, router, hub, etc. 
         [0009]    Each of the APs  10 - 40  has a corresponding coverage area which defines a range over which the AP may transmit and receive radio frequency (“RF”) signals. A mobile unit (“MU”)  50  located within a particular coverage area may communicate with a corresponding AP. The MU  50  may be one of a laser-/imager-based scanner, an RFID reader, a mobile phone, a PDA, a tablet computer, a network interface card, a laptop, a digital camera and a portable media player. The MU  50  may be located in the coverage area of the AP  30  and communicate therewith. The APs  10 - 40  may either be single channel APs (e.g., 2.4 GHz or 5.1 GHz) or multiple channel APs (e.g., 2.4 GHz and 5.1 GHz). Multiple channel APs may potentially support a first channel of single BSS operation, according to the present invention, concurrently with a second channel of single BSS operation or conventional AP operation. 
         [0010]    In a conventional 802.11 network, each AP has a unique BSSid. Thus, if a packet is addressed to and received by an AP (e.g., AP  30 ), the AP  30  will accept the packet and transmit an acknowledgment to the source device (e.g., the MU  50 ). If the packet is not addressed to BSSid for the AP  30 , it is ignored. According to the present invention, every AP (e.g., APs  10 - 40 ) or selected ones of the APs  10 - 40  have the same BSSid. Thus, the MU  50  assumes it is only communicating with a single AP. The system  1  may handle a plurality of MUs at any time, wherein each MU addresses packets to the same BSSid. 
         [0011]    In the exemplary embodiment, the NMA  60  monitors operation and performance parameters of the APs and the MUs. The NMA  60  supplies each AP with a list of MUs with which it should communicate. For example, due to a predetermined set of parameters (e.g., RSSI, TDOA, location load, communication type, etc.), the NMA  60  may include the MU  50  on the list supplied to the AP  30 . Thus, for each packet received by the AP  30 , a source address is compared against the list. If the source address is contained in the list, the AP  30  acknowledges the packet; otherwise the packet may be ignored. The NMA  60  analyzes the set of parameters to update the list for each AP, e.g., moving the address for MU  50  to another AP. 
         [0012]    In addition, the APs  10 - 40  may be synchronized so that they each transmit beacons at substantially the same time. In the exemplary embodiment, one AP is selected by the NMA  60  to serve as a timing master AP. The timing master AP is preferably an AP in a geographically central location relative to the other APs. The timing master AP may set the timing for its beacon, and the remaining APs set their local timing synchronization function (“TSF”) timers to the beacon transmitted by the timing master AP. If any APs cannot hear the beacon transmitted by the timing master AP, a first set of the remaining APs (e.g., “Primary APs”) may also be configured to transmit beacons to the other remaining APs (e.g., “Secondary APs”). The Primary APs synchronize their local TSFs to the beacon from the timing master AP. The Secondary APs may suspend transmissions to avoid interfering with the beacon transmission by the timing master AP and the Primary APs. 
         [0013]    In the exemplary system, other tasks commonly performed in conventional IEEE 802.11 protocols may be altered. For example, in conventional wireless networks, all APs periodically transmit beacons, thereby informing MUs of their presence. However, in the single BSS system, simultaneous transmissions from the APs may collide and consume too much bandwidth. These problems may be overcome by classification of the APs  10 - 40  into Primary APs and Secondary APs, as described above. To prevent collisions and reduce bandwidth consumption, the Primary APs may transmit their beacons at a predetermined offset from one another so as to allow a distributed coordination function (“DCF”) to occur and minimize collisions. The offset is preferably small enough to avoid disrupting normal network operation, but large enough to avoid collisions. The offsets may be fixed by the NMA  60 , or they may be randomly determined by the Primary APs on a per packet basis. A TSF value in each beacon frame may be adjusted to reflect the offset. 
         [0014]    The MU  50  initiates communication with the network  65  by transmitting an association request to an AP whose beacon it has heard. The AP  30  forwards the association request to the NMA  60 , which will either grant or deny it. If more than one AP receives and forwards the association request, the NMA  60  selects the AP which will grant the association request. If the NMA  60  grants the association request, the MU  50  is authenticated and begins communication on the network  65 . Thus, the NMA  60  may control communications between the MU  50  and the APs  10 - 40 . 
         [0015]    In a conventional IEEE 802.11 wireless network, the MU  50  must reassociate and reauthenticate each time it attempts to communicate with a new AP (e.g., when the MU  50  migrates into a different coverage area, determines that the new AP is better suited to handle the MU  50 , etc.). Repetition of the association and authentication procedures delays access to the network  65  for the MU  50 . 
         [0016]    According to the present invention, the MU  50  may communicate with each AP  10 - 40  without having to re-execute the association/authentication process. After the MU  50  initially associates/authenticates with an AP, the NMA  60  may transfer responsibility for the MU  50  to/from each AP. 
         [0017]      FIG. 2  shows an exemplary method  200  for roamless client-side communication according to an embodiment of the present invention. The method  200  will be described with reference to the system  1  of  FIG. 1 . However, it will be understood by those of skill in the art that the method  200  may be implemented in various network architectures. 
         [0018]    In step  210 , the MU  50  transmits an association request to the AP  30 , because the MU  50  hears a beacon therefrom and determines that the AP  30  will provide the best connection to the network  65 . In step  215 , the AP  30  forwards the request to the NMA  60 . The NMA  60  may then grant the request (step  220 ). It will be understood by those of skill in the art that the NMA  60  may alternatively deny the request, depending on a number of factors (e.g., identifying information of the MU  50 , encryption information, current network load, unauthorized MU, etc.). However, for purposes of the present example, it is assumed that the NMA  60  grants the request. The NMA  60  may then notify the AP  30  of its grant of the request. 
         [0019]    In step  225 , the NMA  60  adds the MU  50  to the list of MUs supported by the AP  30 . The list identifies all MUs which communicate with the AP  30 . The MU  50  may then communicate with the AP  30  (step  230 ). That is, the AP  30  will acknowledge packets transmitted by the MU  50 . This will be described in more detail with respect to  FIG. 3 . 
         [0020]    In step  235 , the MU  50  migrates to a coverage area of another AP (e.g., the AP  20 ). The MU  50  continues to transmit packets (e.g., data packets, voice packets, etc.) and the APs that can hear the MU  50  may forward some or all of the packets to the NMA  60 . Because the packets may contain location information (e.g., received signal strength indication (“RSSI”) values) pertaining to the MU  50 , the NMA  60  may determine a location of the MU  50  relative to the APs  10 - 40 . Thus, the NMA  60  may recognize when the MU  50  migrates to another coverage area, e.g., from the coverage area of the AP  30  to the coverage area of the AP  20 . 
         [0021]    In step  240 , the NMA  60  modifies the lists of the APs  20  and  30  by, for example, deleting the MU  50  from the list of the AP  30 , and adding the MU  50  to the list of the AP  20 . Thus, the AP  20  responds to packets from the MU  50 , and the AP  30  does not. Accordingly, the MU  50  communicates with the AP  20  (step  245 ). This procedure may be repeated each time the MU  50  travels to another coverage area or at any other rime determined by the NMA  60 , thereby permitting roamless client-side communication. 
         [0022]    In the method  200  described above, communication with another AP (i.e., the AP  20 ) was initiated by migration of the MU  50  into the coverage area of the AP  20  in step  235 . However, it should be understood that communication with another AP may be initiated in a variety of other circumstances. For example, in another embodiment of the invention, the NMA  60  may transfer responsibility for the MU  50  to another AP based on RSSI values, throughput, load, etc., which may be indicated in packets forwarded from the AP(s) to the NMA  60 . That is, the NMA  60  may receive packets from the APs  20  and  30  regarding the MU  50 , because the MU  50  is in the coverage areas of both the AP  20  and the AP  30 . 
         [0023]      FIG. 3  shows an exemplary method  300  for authorizing communication between an AP and an MU. The method  300  will be described with reference to the system  1  of  FIG. 1 . However, it will be understood by those of skill in the art that any of a variety of network protocols and architectures may be used. In this example, it is to be assumed that the MU  50  has already associated and authenticated with the network  65  through one or more APs  10 - 40 . 
         [0024]    In step  310 , the NMA  60  supplies each AP  10 - 40  with a list of MU addresses. The lists may be modified by the NMA  60  as a function of changes in the wireless network (e.g., MUs move, new APs are added etc.). However, as will be discussed below, each AP only acknowledges transmissions from the MUs that are included on its list. 
         [0025]    In step  320 , the MU  50  transmits a packet (e.g., a voice packet, a data packet, etc.) to the AP  20 . Because the packet includes the BSSid used by the APs  10 - 40 , each AP compares its list against the source address of the packet (step  330 ). For example, the AP  20  searches its list for information such as a medium access control (“MAC”) address, IP address, serial number, etc. which identifies the MU  50 . Accordingly, in step  340 , the AP  20  determines whether the MU  50  is on its list, and thus whether it should acknowledge the packet transmitted by the MU  50 . 
         [0026]    As discussed above with respect to the method  200 , the presence of the MU  50  on a particular AP&#39;s list may be controlled by the NMA  60 . However, according to an alternative embodiment, the APs  10 - 40  may be smart APs, thereby enabled to share lists. For example, as the MU  50  migrates from the coverage area of the AP  30  to that of the AP  20 , the AP  30  may transmit information (e.g., a copy of its list, the entry for the MU  50  on the list, etc.) to the AP  20 . If the AP  20  in step  340  determines that the MU  50  is on its list, the AP  20  transmits an acknowledgment (“ACK”) to the MU  50  (step  350 ). Thereafter, the MU  50  communicates with the network  65  through the AP  20 . However, if the AP  20  determines that the MU  50  is not on the list, the AP  20  will ignore the packet. However, because the NMA  60  recognizes that the MU  50  has transmitted the packet, it may add the MU  50  to the list of another AP (e.g., the AP  30 ) to provide the MU  50  with a connection to the network  65 . 
         [0027]    The method  300  may be optimized in order to reduce a burden on the APs when screening a packet to determine if it was transmitted by an MU on its list. For example, a simple 32 to 128 byte bit map may be indexed using a lower 8 to 10 bits of the source address. Thus, if an addressed bit is 0, the packet is ignored by the AP. If the addressed bit is a 1, then the AP may accept the packet and perform further address searches. As such, a substantial amount of packets transmitted by the MUs not supported by the AP may be filtered out with few instructions. The method  300  may further be optimized by dividing the accepted packets into various hash buckets based upon some number of bits on the source address. Accordingly, packets which passed through the first filtration may be filtered out with merely a few more instructions. 
         [0028]    Transmission of broadcast and multicast packets in the single BSS system may be handled similarly to the beacons. For example, the broadcast/multicast packets may be sent by the NMA  60  to the Primary APs. The Primary APs may transmit the broadcast/multicast packets either immediately upon receipt, or after a delivery traffic indication message (“DTIM”). The broadcast/multicast packets may be transmitted at random delays, thereby minimizing a potential for collisions. 
         [0029]    The single BSS system may also vary from conventional protocols with respect to transmission of probe requests and responses. Particularly, the APs may be configured to ignore probe requests from the MU  50  which are below a specified RSSI threshold. Therefore, a potential conflict of multiple APs attempting to service the MU  50  is decreased. Further, if a first AP hears a response generated by another AP, the first AP may terminate transmission of its probe response. Copies of probe requests may be forwarded by the APs  10 - 40  to the NMA  60 , thereby enabling the NMA  60  to monitor signal strengths of the MU  50  relative to the APs  10 - 40 . 
         [0030]    According to the exemplary embodiment, clear to send (“CTS”) packets may be transmitted by the Primary APs. However, all APs will respect a time interval specified by a request to send (“RTS”) packet. 
         [0031]    The exemplary embodiment may also vary from a conventional system with respect to handling of poll and null packets. Also according to the exemplary embodiment, poll/null packets may be acknowledged by the AP that supports the MU  50 . After the MU  50  transmits the packet, all APs that receive it forward it to the NMA  60 . The poll/null packets may include location information (e.g., RSSI value) relating to the MU  50 , and thus the APs may be configured to forward the packet only if the RSSI is above a predetermined threshold. Upon receiving the packets from the APs, the NMA  60  may select an optimal AP to support the MU  50 , thereby deciding to “roam” based on updated information. Accordingly, even if the MU  50  is disabled (e.g., in power save mode, turned off, etc.) as it migrates out of range of the AP  30 , the NMA  60  may determine that another AP is better suited to support the MU  50 . 
         [0032]    As discussed above, data packets are handled by the AP which supports the MU  50 . According to the exemplary embodiment, other APs, which are not supporting the MU  50 , may additionally forward a predetermined percentage of data packets (i.e., “sample packets”) for the MU  50  to the NMA  60 . These sample packets provide the NMA  60  with additional signal strength information. 
         [0033]    Embodiments of the present invention may also vary from a conventional system with respect to wireless multimedia (“WMM”) scheduling. Many of the WMM scheduling algorithms in conventional systems use beacon transmission time as a basis for controlling access to a channel. According to the exemplary embodiment, a similar WMM scheduling algorithm may be used, despite generation of beacons by only the Primary APs. Because the Secondary APs monitor and synchronize with the beacons transmitted by the Primary APs, they may recognize an appropriate time to transmit packets to their MUs. 
         [0034]    As mentioned above, in the exemplary embodiment “roaming” is performed by the NMA  60 , as opposed to a conventional system wherein it is performed by the MUs. That is, the NMA  60  transfers responsibility for the MU from one AP to another. An algorithm used by the NMA  60  to determine when to perform a roam procedure may be based on a combination of factors. For example, the algorithm may be based on RSSI values, data rates, retry counts, etc. The NMA  60  may receive a significant amount of data corresponding to each MU, because all APs may potentially forward copies of probe requests, copies of association packets, and the sample data packets. However, the roaming algorithm may be tailored to use only the data that it most pertinent to the NMA&#39;s decision. 
         [0035]    The present invention may be efficient in saving costs related to reassociation and reauthentication. Specifically, a user will not experience a delay and/or a terminated communication (e.g., a “dropped call”) because the MU  50  is roaming in another coverage area. Thus, the MU  50  maintains a seamless connection to the network  65 . 
         [0036]    Another advantage of the present invention is that it can be implemented with only minor changes to a wireless switch protocol (“WiSP”). The minor changes may include addition of certain configuration options to the protocol. For example, configuration options for various procedures (e.g, specifying operation in Single BSS mode, specifying whether an AP is a Primary or Secondary, adding and/or removing MU addresses, and specifying a percentage of data packets to be “leaked” to the switch, etc.) may be added. The minor changes may also include indicating to the NMA  60  which packets are for NMA roaming usage. 
         [0037]    The present invention may also be implemented without any client side upgrades. 
         [0038]    The present invention has been described with the reference to the above exemplary embodiments. One skilled in the art would understand that the present invention may also be successfully implemented if modified. Accordingly, various modifications and changes may be made to the embodiments without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings, accordingly, should be regarded in an illustrative rather than restrictive sense.