Abstract:
A protocol for acknowledging receipt of a multicast or broadcast frame by a wireless unit is described. One embodiment, an Eavesdrop Unicast frame is created for use in a wireless network operated in accordance with IEEE 802.11. The Eavesdrop Unicast frame allows the targeted wireless unit to transmit acknowledgement (ACK) frame but is configured so that other wireless units can scan and obtain information therefrom. Another embodiment is similar in configuration to the Eavesdrop Unicast frame but is fully compliant with IEEE 802.11. Therein, a multicast or broadcast frame is transmitted but one wireless unit is configured to acknowledge receipt of the multicast or broadcast frame. The acknowledgement is accomplished through transmission of a data frame. Yet another embodiment is the transmission of broadcast or multicast frames into corresponding unicast frames.

Description:
This application claims benefit of U.S. Provisional Application No. 60/226,343, filed Aug. 18, 2000. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of networking. In particular, this invention relates to a protocol for acknowledging receipt of multicast or broadcast frames communicated over a wireless network. 
   BACKGROUND OF THE INVENTION 
   The ability of users to access programs and share data over local area networks (referred to as “LANs”) has become a necessity for most working environments. To improve efficiency and ease of use, certain enhancements may be added to a LAN such as remote wireless access. By providing remote wireless access, a wireless LAN (WLAN) is formed. 
   As described in U.S. Pat. No. 5,987,062 issued to Netwave Technologies, Inc., now owned by Nortel Networks Limited, one type of WLAN employs dedicated stations, which are referred to as access points (APs). Therein, each AP is a relay station that receives frames from a mobile unit such as a notebook-type computer with a suitable adapter card as described in U.S. Pat. No. 5,987,062. Thereafter, the AP transmits contents of these frames, namely one or more data packets, to the fixed backbone network. 
   Of course, the AP also receives data packets of data from the fixed backbone network for transmission to one or more mobile units. In accordance with Institute of Electrical and Electronics Engineers (IEEE) 802.11 published Nov. 16, 1998 and entitled “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications,” the AP is capable of detecting whether a data packet is directed toward a specific mobile unit (referred to as “unicast frame”). Such detection is accomplished by examining a destination address from the incoming data packet and comparing this address to Media Access Control (MAC) addresses for each of its authenticated mobile units. The MAC addresses are stored in an address table maintained within the AP. If a match is detected, the data packet is sent to a wireless transceiver interface  210  to produce a unicast frame having the MAC address as its destination address. Upon receiving the contents of the unicast frame, the mobile unit transfers an acknowledgement (ACK) frame to the AP in accordance with IEEE 802.11. 
   Besides unicast transfers, the AP also supports the transmission of data frames to a group of mobile units (referred to as “multicast frames”) or to all of the mobile units (referred to as a “broadcast frames”). In accordance with IEEE 802.11, the delivery of multicast and broadcast frames is not reliable because ACK frames are not required from the mobile units. Currently, there is no protocol for the AP to confirm whether any of its multicast or broadcast frames have been successfully received by the MUs. Since information within the multicast or broadcast frames may be vital to the operations of the WLAN, insuring their receipt would enhance the capability of the APs. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a protocol for acknowledging receipt of a multicast or broadcast frame by a wireless unit is described. One embodiment, an Eavesdrop Unicast frame is created for use in a wireless network operated in accordance with IEEE 802.11. The Eavesdrop Unicast frame allows the targeted wireless unit to transmit acknowledgement (ACK) frame but is configured so that other wireless units can scan and obtain information therefrom. 
   Another embodiment is similar in configuration to the Eavesdrop Unicast frame but is fully compliant with IEEE 802.11. Therein, a multicast or broadcast frame is transmitted but one wireless unit is configured to acknowledge receipt of the multicast or broadcast frame. The acknowledgement is accomplished through transmission of a data frame. Yet another embodiment is the transmission of broadcast or multicast frames into corresponding unicast frames. 
   Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying claims and figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become apparent from the following detailed description of the present invention in which: 
       FIG. 1  is a first exemplary embodiment of a wireless network. 
       FIG. 2  is an exemplary embodiment of an access point (AP) of a wireless network. 
       FIG. 3  is a second exemplary embodiment of a wireless network. 
       FIG. 4  is a first exemplary embodiment of a flowchart illustrating a protocol for acknowledging receipt of one or more cast frames. 
       FIG. 5  is an exemplary embodiment of the cast frame utilized in the protocol of  FIG. 4 . 
       FIG. 6  is an exemplary embodiment of a data frame for acknowledging receipt of the cast frame of  FIG. 5 . 
       FIG. 7  is a second exemplary embodiment of a flowchart illustrating a protocol unicast for acknowledging receipt of frames translated from a cast frame. 
       FIG. 8  is an exemplary embodiment of an Eavesdrop Unicast frame. 
       FIG. 9  is an exemplary embodiment of a translation from the Eavesdrop Unicast frame of  FIG. 8  to a data frame for processing by the WU. 
       FIG. 10  is a third exemplary embodiment of a flowchart illustrating a protocol for acknowledging receipt of an Eavesdrop Unicast frame of  FIG. 8 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Herein, the exemplary embodiments of the present invention relate to a protocol for acknowledging receipt of multicast and broadcast frames by a wireless unit employed within a wireless network (WLAN). The WLAN may be configured in accordance with Institute of Electrical and Electronics Engineers (IEEE) 802.11 or subsequently published specifications. These embodiments are not exclusive; rather, they merely provide a thorough understanding of the present invention. Well-known circuits are not set forth in detail in order to avoid unnecessarily obscuring the present invention. 
   In the following description, certain terminology is used to describe features of the present invention. For example, “logic” includes hardware and/or software module(s) that perform a certain function on incoming information. A “software module” is executable code such as an operating system, an application or an applet for example. The module may be stored in any appropriate storage medium such as a hard drive a CD-ROM, memory (non-volatile or volatile), tape, etc.) The term “information” is defined as data, address, and/or control. For transmission, the information may be placed in a frame featuring a single packet or a series of packets, where each packet features a predetermined number of bits of information. 
   In addition, a “link” is broadly defined as one or more information-carrying mediums to establish a communication pathway. Examples of the medium include a physical medium (e.g., electrical wire, optical fiber, cable, bus traces, etc.) or a wireless medium (e.g., air in combination with wireless signaling technology). 
   Referring to  FIG. 1 , an exemplary first embodiment of a wireless network system  100  in accordance with the invention is illustrated. The wireless network system  100  comprises a link  101  based on a physical medium. Herein, the link  101  is part of a wired backbone network  102  that includes network resources  104  available for users of the network  100 . The wireless network system  100  further includes one or more access points (APs)  106   a - 106   d  that communicate via a wireless link with one or more wireless units (WUs)  108   a - 108   f . For this embodiment, four (4) APs  106   a - 106   d  communicate with six (6) WUs  108   a - 108   f  as described below. 
   Users using the WUs  108   a - 108   f  can access the network resources  104  via any of the APs  106   a - 106   d , which are generally transparent bridges that link a wireless network defined by one or more WUs  108   a - 108   f  with the wired backbone network  102 . The WUs  108   a - 108   f  communicate with the APs  106   a - 106   d  typically using a standardized protocol, such as the IEEE 802.11 protocol. 
   A “wireless unit” (WU) is defined herein as any electronic device comprising (1) logic for processing information (e.g., a processor, microcontroller, state machine, etc.) and (2) a wireless transceiver for receiving information from and transmitting information to an access point (AP) or another wireless unit (WU). Examples of an “electronic device” include a computer (e.g., desktop computer, laptop computer, hand-held computer such as a personal digital assistant “PDA”, etc.), communications equipment (e.g., pager, telephone, facsimile machine, etc.), a television set-top box, or appliances such as refrigerator pads, electronic picture frames, alarm detectors, water detectors, and the like. 
   An “access point” (AP) is an electronic device that provides a bi-directional connection between one or more WUs and a network such as the wired backbone network  102 . However, an AP could also have a wireless connection back to the wired backbone network  102 , such as AP  106   d , which has a wireless link to the backbone network  102  via another AP  106   c . The wired backbone network  102  can be of any type, including an Ethernet, a token ring, or an asynchronous transfer mode (ATM) network. 
   Referring now to  FIG. 2 , an exemplary embodiment of an access point (AP) is shown. For illustrative purposes, the access point is represented by AP  106   b  and differs in function from the access points described in U.S. Pat. No. 5,987,062. As shown, AP  106   b  comprises logic  200  and  202 , an address table  204 , a device management logic  206 , and a wireless transceiver interface  210 . In particular, the logic  200  is used to determine whether certain information from the wired backbone network  102  is destined for one or more of the WUs. The address table  204  includes Medium Access Control (MAC) addresses for all of the wireless units associated with the AP  106   b  such as WUs  108   c  and  108   d  of  FIG. 1 . In the special case of all broadcast or some multicast packets, the packets are addressed to all or some of the WUs associated with the AP  106   b  on a “best effort” basis. 
   Similarly, as information from the WUs is received by the wireless transceiver  210 , the logic  202  monitors addresses within this information against the contents of the address table  204 . One reason is that only information from authenticated and associated wireless units (e.g., WUs  108   c  and  108   d ) is accepted. Hence, if information is received from a non-authenticated wireless unit, the information will not be forwarded to the wired backbone network  102  of  FIG. 1 . If the information is received from an authenticated wireless unit, the logic  202  subsequently transmits the information to the logic  200  for routing to the wired backbone network  102 . 
   In the event that the fixed backbone network  102  of  FIG. 1  has a substantially larger data rate than the wireless network, content addressable memory (CAM)  212  and a hardware address filter (HAF)  214  may be employed within the AP  106   b . The CAM  212  and HAF  214  are in communication with the wired backbone network  102  and collectively filter information at the physical layer. For example, the HAF  214  examines an incoming packet from the wired backbone network  102  to determine if the destination MAC address is in its own internal table  215 . The internal table  215  includes MAC addresses of devices reachable to the wired backbone network  102 , namely directly coupled to the network  102  or indirectly through another AP for example. Thus, the logic  200  needs only process a portion of the information routed over the wired backbone network  102 . 
   The device management logic  206  provides a mechanism for adjusting the various parameters and controlling the functionality of the AP  106   b . In one embodiment, the device management logic  206  compares a destination MAC address of an incoming packet from network  102  with the MAC addresses stored within the address table  204 . If a successful match is detected, the MAC address will be placed in an outgoing unicast data frame to the targeted WU. 
   The device management logic  206  may be configured via a port interface  216  within the AP  106   b . The port interface  216  (e.g., a serial port) provides a direct connection to the AP  106   b . Other mechanisms include (1) Simple Network Management Protocol (SNMP) management tools such as OPTIVITY® by Nortel Networks Limited, (2) TELNET, or (3) web-based management software. 
   Referring back to  FIG. 1 , in the typical scenario, a WU associates itself with one of the APs to communicate with the wired backbone network  102 . For instance, in the example shown in  FIG. 1 , WUs  108   a  and  108   b  are associated with AP  106   a , WUs  108   c  and  108   d  are associated with AP  106   b , WU  108   e  is associated with AP  106   c , and WU  108   f  is associated with wireless AP  106   d . Which AP a wireless unit (WU) is associated with can depend on many factors, including signal quality, load balancing, restricted links and other factors. The AP that a particular WU is associated with can change, such as when the WU “roams” from the coverage area of a particular AP to a coverage area of another AP. From the standpoint of the user using the WU, this change in associated AP is transparent. 
     FIG. 3  illustrates a second exemplary embodiment of a wireless network system  300  in accordance with the invention. The wireless network system  300  comprises two or more sub-networks  302   a  and  302   b , which communicate with each other by way of a router  304 . The sub-networks  302   a  and  302   b  can be any wired backbone network, including Ethernet, token ring, and an asynchronous transfer mode (ATM) network. The sub-networks  302   a  and  302   b  need not be of the same type, for instance, sub-network  302   a  can be an Ethernet, and sub-network  302   b  can be a token ring. Each sub-network  302   a  and  302   b  has one or more APs for communicating with the WU. For instance, sub-network  302   a  includes APs  306   a - 1 ,  306   a - 2 ,  306   a - 3  for communicating respectively with WUs  308   a - 1 ,  308   a - 2 , and  308   a - 3 . Sub-network  302   b  includes APs  306   b - 1  and  306   b - 2  for communicating respectively with WUs  308   b - 1  and  308   b - 2 . In this network, a WU associated with an AP on a particular sub-network (e.g. sub-network  302   a ) can also change its association to an AP on another sub-network (e.g. sub-network  302   b ) by roaming as discussed above or other circumstances. 
   Referring now to  FIGS. 4-6 , a first exemplary embodiment of a protocol (fully compliant with IEEE 802.11) for acknowledging receipt of one or more multicast and/or broadcast frames (referred to universally as “Cast frames”) over wireless network system  100  or  300  is shown. These Cast frames are data frames in accordance with IEEE 802.11 as shown in  FIG. 5 . A first address field  510  of the Cast frame  500  is set to a particular MAC address assigned to a group of WUs when the Cast frame  500  is a multicast frame. Similarly, the first address field  510  is set to a predetermined value (e.g., all bits are set) when the Cast frame  500  is a broadcast frame. A second address field  520  of the Cast frame  500  includes an address associated with the AP transmitting the Cast frame  500 . 
   Referring back to  FIG. 4 , one of the WUs is initially selected for acknowledging receipt of all Cast frames for a particular AP (block  400 ). The selection of the WU may be directed toward either (i) minimizing retransmissions of the Cast frame or (ii) maximizing the likelihood that all WUs will actually be able to hear the Cast frame. In order to minimize retransmissions, the AP may analyze levels of signal quality associated with frames most recently received by the WUs and select the WU with the highest level of signal quality. In order to maximize the likelihood of hearing the Cast frame, however, the AP may select the WU with the lowest power level. It is contemplated, however, that another selection technique may be used. At some time after selection of the WU, a Cast frame is transmitted to two or more WUs including the selected WU (block  410 ). 
   In response to receiving the Cast frame (blocks  420  and  430 ), the selected WU transmits to the AP a data frame  600  in accordance with IEEE 802.11 in order to acknowledge receipt of the Cast frame (block  440 ). As shown in  FIG. 6 , the data frame  600  includes the contents of the second address field  520  of the Cast frame  500  of  FIG. 5  within a first address field  610  of the data frame  600 . This differs from any normal acknowledgement protocols in which the ACK frame is a control frame. If the AP does not eventually receive data frame  600 , cast frame  500  is retransmitted. 
   Referring now to  FIG. 7 , a second exemplary embodiment of a protocol for acknowledging receipt of one or more Cast frames over wireless network system  100  or  300  is shown. When an AP determines that a Cast frame is scheduled for transmission, the Cast frame is translated into multiple unicast frames (blocks  700  and  710 ). The determination of whether the Cast frame is scheduled for transmission may be accomplished by either active notification of the device management logic (e.g., signal from as the HAF) or passive notification (e.g., computed by the device management logic based on quantitative data). These unicast frames are addressed with the MAC addresses for the WUs stored in the address table of the AP. Thus, in lieu of transmitting the Cast frame, multiple unicast frames are transmitted in succession to the WUs associated with the AP (block  720 ) and await a return acknowledgement (ACK) frame from one or more of the WUs. 
   Referring now to  FIGS. 8-10 , a third exemplary embodiment of a protocol for acknowledging receipt of an Eavesdrop Unicast frame, which is transmitted over wireless network system in lieu of a multicast or broadcast frame. Herein, the Eavesdrop Unicast frame  800  comprises a frame control field  810  including a type field  811 , a subtype field  812 , first-fourth address fields  820 - 823 , a payload field  830  and a frame check sequence (FCS) field  840 . The type field  811  would be set to indicate that the Eavesdrop Unicast frame  800  is a data frame. The subtype field  812  would be loaded with data to identify that the new subframe type is the Eavesdrop Unicast frame  800 . 
   With respect to the address fields  820 - 823  of the Eavesdrop Unicast frame  800 , the first address field  820  includes a destination address of the targeted WU in lieu of a value to identify the frame as a standard broadcast or multicast frame. The fourth address field  823  includes a particular MAC address assigned to a group of WUs when the Eavesdrop Unicast frame  800  is a multicast frame, which is normally placed in the first address field of a standard multicast frame. Alternatively, the fourth address field  823  is set to a predetermined value (e.g., all bits are set) when the Eavesdrop Unicast frame  800  is a broadcast frame. 
   As shown in  FIG. 9 , the translation from the Eavesdrop Unicast frame to a data frame  900  for processing by the WU is shown. In particular, the contents from the fourth address field  823  are loaded as the contents of a first address field  920  of the data frame  900 . Thereafter, contents of the Eavesdrop Unicast frame  800  are loaded into corresponding fields of the data frame  900  such as the contents of the payload fields  830  and  930 , contents of the second and third address fields  821 ,  921 ,  822  and  922 . As shown, the contents of the first address field  920  are loaded by the contents from the fourth address field  823  of the Eavesdrop Unicast frame  800 . The bits associated with the fourth address field  823  of the Eavesdrop Unicast frame are removed and are not existent in the data frame  900 . 
   Referring now to  FIG. 10 , a flowchart associated with the protocol for acknowledging receipt of an Eavesdrop Unicast frame is shown. Herein, the Eavesdrop Unicast frame is initially transmitted to a targeted WU; however, the other WUs associated with the AP are required to scan to the particular channel carrying the Eavesdrop Unicast frame (blocks  1000  and  1010 ). The selection of the targeted WU may be based on signal quality levels associated with frames most recently received by the WUs, perceived power levels of incoming frames or other characteristics. 
   In response to receiving the Eavesdrop Unicast frame (block  1020 ), the selected WU overwrites the first address field  820  with the contents of the fourth address field  833  and removes the fourth address field  823  from the received frame (blocks  1030  and  1040 ). The second and third address fields  821  and  822  still include the MAC address associated with the AP and originating device, respectfully. 
   Additionally, the selected WU transmits an acknowledgement (ACK) frame in accordance with IEEE 802.11 to the AP (block  1050 ). The ACK frame indicates that the selected WU has received the Eavesdrop Unicast frame and provides an inference that most or all of the other WUs likely listened and received the contents of the Eavesdrop Unicast frame as well. 
   While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.