Abstract:
One embodiment described herein, a method of supporting wireless stations in a wireless distribution system having a portal and one or more access points is described. The method comprises accepting by a first access point (AP) a set of filters from a station; receiving by the first AP signaling that the station enters into an idle mode and signaling the same to a server in the wireless distribution system; forwarding by the first AP the set of filters to the server, the set of filters being applied to messages directed to the station received by the server in the wireless distribution system; receiving a buffered message for the station from the server in response to the buffered message matching at least one of the set of filters; and forwarding the buffered message to the station in response to receiving the buffered message from the server.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority from U.S. Application No. 11/830,752 (Attorney Docket No. 6259P032), filed on 07 Jul. 2007, now U.S. Pat. No. ______, the entire contents of which are incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention pertains to wireless local area networks (WLANs), and more particularly, to methods of supporting idle stations in WLANs and wireless distribution systems (DS) operating under IEEE 802.11 standards. 
         [0003]    In wireless local area networks, such as networks using the 802.11 model, consist of stations (STA) which are associated with access points (APs), which are in turn connected to a distribution system (DS). It should be noted that the DS is an abstract concept, and is not restricted to a particular implementation or technology. 
         [0004]      FIG. 1  shows a wireless DS connected to a wired network as known to the art. DS  100  connects to wired network  200  through portal  110 . Access points,  112 ,  114 ,  116 ,  118  provide wireless access to stations  120 ,  122 ,  124 . As is known to the art, when a station associates with an AP, the DS is notified of this event so that incoming packets destined for the station are routed to the proper AP for delivery. 
         [0005]    When a station is associated with an AP, such as station  124  associated with AP  116 , implicit information is exchanged in order to keep the association state alive at both ends. For example, a STA may indicate to the AP that it is either going into power-save state or out of it by either setting bits in regular messages it sends to the AP or by sending a NULL data frame (a data frame with no payload) with bits in the header indicating change of state. The AP may set specific bits in the TIM (traffic indication map) information element in its beacons informing stations in power-save state that there may be packets buffered for them at the AP. Even though no explicit keepalive messages are exchanged, there is an expectation that an active connection be maintained by the station at all times. 
         [0006]    In draft submission, document IEEE 802.11-07/2169r0 to the IEEE P802.11 group titled “Traffic Filtering and Sleep mode” on wireless LANs (incorporated herein by reference), a set of protocols and messages for supporting traffic filtering and idle mode is proposed. 
         [0007]    While the draft defines messages and behavior, it does not specify implementation details. Under the proposal, a station associated with an AP may specify filter parameters indicating what traffic it wishes to accept. When the station goes into sleep mode, it is no longer associated with a particular AP. The station is paged when traffic passing the pre-established filter criteria is met. When the station wakes from the sleep state, it reassociates with an AP. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention may be best understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. 
           [0009]      FIG. 1 . shows a block diagram of a wireless distribution system (DS) as known to the art; 
           [0010]      FIG. 2  shows a block diagram of a DS including a paging server; and 
           [0011]      FIG. 3  shows a second block diagram of a DS including a paging server. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Embodiments of the invention relate to a distribution system (DS) in a wireless IEEE 802.11 data network. In an embodiment of the invention, as shown in  FIG. 2 , sleep mode server  130  appears to DS  100  as another access point (AP). In operation, when a station such as station  124  goes into idle mode, it is associated with server  130 . Once this association is made, DS  100  will direct traffic destined for station  124  to server  130 . Server  130  buffers this traffic and initiates the process of paging station  124  by all APs within the DS. When station  124  exits idle mode and reassociates with DS  100 , for example through AP  116 , server  130  is notified of this event and sends the buffered traffic to station  124  through its associated AP. 
         [0013]    Battery life is an important consideration in portable devices. A primary means of increasing battery life in a portable device is to reduce the power used by the device. One approach to reducing power, particularly in digital devices, is to use idle or sleep modes, wherein major portions of the device are operated in low power modes, or disabled completely. 
         [0014]    Such reduced power modes introduce additional complexity, however, into wireless devices. In accordance with IEEE 802.11 wireless networking standards, once a station (STA) is associated with an access point (AP) which provides wireless services to that station, a fairly constant exchange of messages between AP and station continues, performing tasks such as synchronization. For wireless stations, listening for, and responding to these messages consumes power. 
         [0015]    The IEEE 802.11 standard defines optional power save modes in which the station signals to the AP it is associated with that it wishes to enter a sleep state. If the AP supports sleep states, the AP acknowledges the request, and begins buffering packets for the station. This allows the station to reduce power to its wireless circuitry, while still maintaining an association with a specific AP. The AP still sends out regular beacon transmissions; if an AP has packets buffered for a sleeping station, it indicates this in the beacon transmissions. Sleeping stations wake periodically and check these beacon transmissions to see if the AP has packets waiting for it. If there are packets waiting, the station exits sleep mode, and retrieves the packets. The packets may require further activity, such as accepting an incoming VOIP call, or if no further activity is required, the station may transition back to sleep mode. Note that during this sleep mode, the station is still associated with an AP. 
         [0016]    Buffering packets for sleeping clients is an expensive task for APs, requiring large buffers and complex management strategies. 
         [0017]    Revisions to the 802.11 standard, such as those contemplated in the referenced proposal, include the addition of an “idle mode” where a station is not required to maintain an active association with a specific AP in the DS while it is in the idle mode. It is contemplated that this new “idle mode” will result in more power savings, since the station is no longer associated with a particular AP. The proposal also specifies messages and behavior for the station to specify a set of traffic filters, indicating what traffic the station wishes to be notified of. The proposal is also quiet on how these are to be implemented. 
         [0018]    According to the present invention, a sleep mode server  130  is established for DS  100 . Stations  120 ,  122 ,  124  associate with APs which are part of the DS. In the example of  FIG. 2 , station  124  is associated with AP  116 . In accordance with the present invention, when station  124  associated with AP  116  establishes filters indicating the types of traffic the station wishes to receive, AP  116  forwards these filters to server  130 . When station  124  enters idle mode, it is disassociated from AP  116 . AP  116  signals server  130  when station  124  enters idle mode. Server  130  then signals DS  100  that station  124  is associated with it, with server  130 . 
         [0019]    Once associated with server  130 , all traffic destined for station  124  goes to server  130 . When packets arrive at server  130  for idle station  124 , server  130  applies the previously set filters. When a packet satisfying the filter criteria for station  124  is met, server  130  pages station  124  through all APs defined for DS  100 . When station  124  exits idle mode on decoding a page, it reassociates with an AP, for example AP  116 . This reassociation is broadcast to all APs in DS  100 , which includes server  130 . When server  130  receives this reassociation information it then forwards saved packets for station  124  to the station&#39;s current AP, now AP  116 . 
         [0020]    It should be noted that while server  130  may functionally resemble an AP in DS  100 , it does not transmit or receive wireless traffic. Rather, it stores filter settings and buffers traffic for idle stations which have been associated with it, initiates paging for idle stations through all APs associated with the DS, and forwards buffered frames to those stations when they exit the idle state and reassociate with an AP in the DS. 
         [0021]      FIG. 3  shows a block diagram of a DS including a server according to an embodiment of the present invention. Portal  110  connects to wired network through network interface  300 . Access points  112 ,  114 ,  116 , and  118  also attach to portal  110 . Portal  110  has CPU  310  and memory hierarchy  320  which communicates  330  with network interface  300  and network interfaces  340 ,  343 ,  344 . Depending on the complexity of portal  110 , the communication  330  among CPU, memory, and network interfaces may be simple interconnections and busses, or may be a more complex switching fabric. Memory hierarchy  320  typically contains high speed read-write memory as well as nonvolatile memory such as flash. Memory hierarchy  320  contains instructions and data which are executed or interpreted by CPU  310  to perform the various tasks and processes described herein. CPU  310  may be any suitable processor, such as those in the PowerPC, MIPS, or IA86 families. 
         [0022]    Network interfaces  300 ,  340 ,  343 ,  344  are typically Ethernet interfaces, with interfaces  340 ,  342 ,  344  optionally supporting IEEE 802.3 Power over Ethernet (PoE) standards such as 802.3af and 802.3at to provide power to APs  112 ,  114 ,  116 ,  118 . 
         [0023]    Access points (APs)  112 ,  114 ,  116 ,  118  are shown in a block diagram as representative AP  116 . Network interface  400  connects to CPU  410  and memory hierarchy  420 , and to radio  430 . Radio  430  is typically a radio module designed for use with the 802.11a, b, g, or n standards. Such radio modules are available from Atheros Communications, among others. An AP may contain one or more radio modules. As an example, separate radio modules may be used for 2.4 GHz 802.11b/g/n and 5 GHz 802.11a. CPU  410  is typically a processor designed for embedded systems, such as a member of the MIPS family. Memory hierarchy  420  usually includes high speed read-write memory such as DRAM, as well as non-volatile memory such as flash. Memory hierarchy  420  contains instructions and data which are executed or interpreted by CPU  410  to perform the various processes and tasks described herein. In operation, an AP such as AP  116  may have all the programming information, code and data, required already present in memory  420 . In other implementations an AP may only contain enough programming information in memory  420  to start up the AP and download further programming information from portal  110 . In a highly integrated AP, CPU  410 , network interface  400 , and much of the support logic required for memory hierarchy  420  and radio  430  may be integrated into one or more complex integrated circuits, usually identified as system-on-chip (SOC) design. 
         [0024]    As is understood by the art, such embedded systems as APs  112 ,  114 ,  116 ,  118  and portal  110  run under the control of an operating system such as one of the many Linux family of systems, or a proprietary system such as VxWorks. 
         [0025]    According to an embodiment of the present invention, server  130  is a function of DS  100 . Since server  130  does not require the ability to handle radio traffic directly, server  130  may be implemented as a process running in DS  100 , as an example, in portal  110 . While paging server  130  may be run as a process in an AP such as AP  112 , or  114 , APs are usually more resource-limited than controllers, with controller  110  most likely containing more memory and a faster processor than those used in the attached APs. Paging server  130  may also be hosted on separate hardware, such as a repurposed AP. In one embodiment, such a repurposed AP need not contain radios  430 , and may contain additional read-write memory in memory hierarchy  420  to support additional buffering of traffic for idle stations. 
         [0026]    In an embodiment such as that shown in  FIG. 3 , portal  110  controls a plurality of APs, which may represent one or more distribution systems (DS). Similarly, portal  110  may host multiple instances of server  130 , one for each DS it serves. 
         [0027]    While the invention has been described in terms of several embodiments, the invention should not be limited to only those embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is this to be regarded as illustrative rather than limiting.