Improved communications throughput with multiple physical data rate transmission determinations

BACKGROUND

1.

Field

of the Invention

0001The present invention relates generally to communications networks and more particularly to a system for increased data throughput in communications networks.

2.

Description of the Prior Art

0002Demand for multimedia applications, including audio and video data, is rapidly increasing. Some of the more popular uses of multimedia are real-time interactive applications, such as video and audio streaming, Internet Protocol TV (IPTV), transmission of lectures or speeches to a remote audience, and animated simulations. Even when data compression is used, multimedia applications require large amounts of bandwidth.

0003In an IEEE 802.11 wireless local area network (LAN), broadcast, or multicast packet transmission enables bandwidth-intensive multimedia applications to simultaneously transmit audio and video data packets to each receiving node associated with a group of the wireless LAN. Broadcast packets are transmitted to all receiving nodes of the wireless LAN, whereas multicast packets are transmitted to two or more, but fewer than all, of the receiving nodes of the wireless LAN.

0004In the wireless LAN, a source node may transmit (e.g., via Ethernet) multicast packets to a multicast-enabled access point, and the access point sends the multicast packets via wireless transmission to destination receiving nodes that have identified themselves as part of the multicast group.

0005The access point of the wireless LAN may also support unicast packet transmission. For unicast transmission in the wireless LAN, the access point transmits one or more unicast packets to the receiving node identified by an intended destination address included in the unicast packets. After receiving the unicast packet, the receiving node transmits (approximately 9µs later) an 802.11 acknowledgement (ACK) packet back to the access point. The 802.11 ACK mechanism provides reliable data transmission in the typically highly interfered 802.11 wireless network by confirming to the access point that the unicast packet was received.

0006A limitation with transmitting multicast packets in the wireless LAN is that the 802.11 ACK does not provide a reliable mechanism for ensuring that the receiving nodes actually received the multicast packets. For example, if the 802.11 access point were to transmit one or more multicast packets to a number of receiving nodes, and each of the receiving nodes were to respond essentially simultaneously with 802.11 ACK packets, the multiple ACK packets received by the access point would comprise "noise" during the period of the multiple simultaneous 802.11 ACKs. To the access point, these multiple simultaneous 802.11 ACKs are undecipherable. This condition may be referred to as a "multiple ACK problem."

0007Another limitation with transmitting multicast packets is that the wireless LAN may be limited in the bandwidth used for multicast packets. Because of the multiple ACK problem, the IEEE 802.11 specification for multicast dictates that transmission of multicast packets occur at a minimum allowable physical data rate. Because the receiving nodes may be at various distances from the source of the transmission, and may experience various interference levels, transmitting at the minimum allowable physical data rate improves the probability of reception of the multicast packets by each receiving node. For example, an 802.11 access point transmits multicast packets at a minimum allowable physical data rate of 1 Mbps for 802.11 band 6 Mbps for 802.11a. The receiving nodes do not transmit 802.11 ACK packets to verify reception of the multicast packets. Thus, without the 802.11 ACK mechanism, there is no verification of reception of the multicast packets.

0008Further, transmitting at the minimum allowable physical data rate under-utilizes available bandwidth in the wireless LAN, which otherwise is capable of supporting much higher data rates. In addition, transmitting at the minimum allowable physical data rate may make the wireless LAN unsuitable for applications that require high rate communication, such as multimedia applications.

0009An example for a wireless network is described in <patcit id="pcit0001" dnum="US20040190477A1"><text>US 2004/0190477 A1</text></patcit>. This wireless network is dynamically reconfigurable and connects a local area network to wireless mobile stations via wireless access points. Dynamic reconfiguration of the access points prevents single point of failure and minimizes transmission hops or maximizes signal strength between mobile stations and the local area network. An access point updates its distribution routing tables when address resolution protocol messages are received from other access points. Further, address resolution protocol messages are transmitted using unicast transmissions, in order to eliminate the flooding of the network.

SUMMARY OF THE INVENTION

0010The invention is defined in independent claim 1. Particular embodiments of the invention are set out in the dependent claims

0011The invention addresses the above problems by providing a system for improved data throughput in wireless local area communications networks. The system comprises a first node and a second node. The first node of the communications network transmits to a second node of the communications network and determines a first physical data rate for transmitting to the second node a multicast or broadcast packet. The first node also determines a second physical data rate for transmitting to the second node one or more unicast packets resulting from conversion of the multicast or broadcast packet into the one or more unicast packets. The first node then transmits the one or more unicast packets to the second node if the second physical data rate exceeds the first physical data rate and otherwise transmits the multicast or broadcast packet to the second node

0012Advantageously, the first node converts the multicast or broadcast packet, when appropriate, to one or more unicast packets and transmits the one or more unicast packets sequentially to the second node at a higher data rate than the minimum physical data rate specified for multicast or broadcast transmission. The first node may comprise a multicast-enabled access point. In some embodiments, the first node determines a third rate by which the first node may transmit the multicast or broadcast packet to a third node of the communications network and transmits over the communications network the multicast or broadcast packet to the second node and the third node at the lower of the first rate and the third rate.

0013Therefore, the systems and methods may provide reliable transmission of the multicast or broadcast packet over the wireless LAN by converting the multicast or broadcast packet to the one or more unicast packets and servicing corresponding acknowledgement packets from the station. A further advantage is that the system may determine not to convert the multicast or broadcast packet, and may transmit the multicast or broadcast packet over the wireless LAN at a higher data rate than the minimum physical data rate that the station may reliably receive.

BRIEF DESCRIPTION OF THE DRAWINGS

0014<figref idref="f0001">FIG. 1</figref> illustrates a block diagram of a system for multicast transmission in a wireless local area network, in accordance with one embodiment of the present invention;

0015<figref idref="f0002">FIG. 2</figref> illustrates an exemplary method for multicast or unicast transmission in the wireless local area network of <figref idref="f0001">FIG. 1</figref>, in accordance with one embodiment of the present invention; and

0016<figref idref="f0003">FIG. 3</figref> illustrates an exemplary timing diagram illustrating conversion of multicast packets into unicast packets as described with respect to <figref idref="f0001 f0002">FIGS. 1-2</figref>, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

0017The systems and methods disclosed herein enable data throughput in communication networks greater than that which is provided in the prior art. For example, the system and method disclosed herein support bandwidth-intensive multimedia applications over wireless LANs. In the disclosure, nodes of a communication network may be referred to as a host, a source, a destination, a node, a receiving node, an access point, and a station. The references should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated. For example, a "receiving node" is in no way limited to the function of receiving only. Additionally, the term group packet includes a multicast packet, a broadcast packet, and any packet whose destination address indicates one or more addresses and/or nodes of the communications network.

0018According to one embodiment, a wireless local area network (LAN) comprises an access point configured to receive a multicast or broadcast packet from a source. The multicast or broadcast packet is addressed to a group comprising one or more nodes of a communications network (e.g., stations associated with the access point of the wireless LAN). The access point determines whether to convert the multicast or broadcast packet into one or more unicast packets for sequential transmission to the one or more nodes or whether to transmit the multicast or broadcast packet to the group. If the access point transmits the multicast or broadcast packet without conversion, the access point may determine a lowest common denominator data rate based on data rates for transmitting multicast or broadcast packets to the one or more nodes and transmits the multicast or broadcast packet to the group at the lowest common denominator rate.

0019<figref idref="f0001">FIG. 1</figref> illustrates a block diagram of a system 100 for multicast packet transmission in a wireless local area network, in accordance with one embodiment of the present invention. The system 100 comprises a source node 110, a network link 115, an access point 120, receiving nodes 130, 140, and 150, wireless links 135, 145, and 155, and a group 160 comprising two or more of the receiving nodes (e.g., the receiving nodes 130 and 140). The source node 110 is configured to communicate with the access point 120 over the network link 115. The access point 120 is configured to communicate with the receiving nodes 130-150 over the wireless links 135-155 that form the wireless LAN.

0020The source node 110 is any device capable of network communication including unicast or multicast packet transmission with the access point 120 over the network link 115. The source node 110 may comprise, for example, a personal computer, a server, a network attached storage device, or a network video distribution device. The source node 110 may support networking protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP), User Datagram Protocol (UDP/IP), and/or Internet Group Management Protocol (IGMP), and may support unicast, multicast, and/or broadcast packet transmission of network data.

0021The source node 110 is configured to transmit one or more group packets addressed to the group 160 (e.g., one or more multicast or broadcast packets) over the network link 115. The network link 115 may be a wired or wireless network link. In one embodiment, the network link 115 comprises a UDP/IP connection. In one example, the source node 110 comprises an IPTV video server (not shown) that transmits the multicast packets, providing a remote video stream to the group 160 through the access point 120. Although discussed in regard to multicast transmission, the group packets may comprise a packet whose destination address specifies all (i.e., broadcast), or less than all (i.e., multicast) of the receiving nodes 130-150.

0022The receiving nodes 130-150 each comprise any device capable of receiving network communication from the source node 110 through the access point 120 over the wireless links 135-155. The receiving nodes 130-150 may comprise devices such as personal computers, PDAs, cell phones, and/or internet enabled televisions. In one example, the receiving nodes 130-140 of the group 160 may comprise TV set-top boxes configured to receive a video stream provided by the IPTV server at the source node 110 to the group 160. Although described as the source node 110 and the receiving nodes 130-150, it should be noted that the source node 110 may also be the destination node of a data packet as well as the receiving nodes 130-150 may also be the source node of a data packet.

0023As described further herein, the access point 120 is configured to transmit the video stream to the receiving node 130 and the receiving node 140 either simultaneously as a multicast packet, or sequentially as one or more unicast packets to each of the receiving nodes 130 and 140. The access point 120 is virtually any device capable of acting as a bridge in a peer-to-peer connection in the wireless LAN or as a bridge between the network link 115 and the wireless links 135-155. The access point 120 may be configured to convert the multicast packet into one or more unicast packets, as discussed further with respect to <figref idref="f0002">FIG. 2</figref>. The access point 120 may include a processor, a memory, and additional circuitry that provides or assists in providing the bridge and/or the multicast packet conversion. The access point 120 may use the IEEE 802.11 protocol, such as 802.11a or 802.11b, to communicate with the receiving nodes 130-150. It will be appreciated that the access point 120 may incorporate other wireless protocols, such as 802.11g, 802.16, or Bluetooth.

0024The access point 120 may support multicast control protocols, such as IGMP, and may be configured as a multicast-enabled router. A multicast control protocol enables the access point 120 to determine from the receiving nodes (e.g., the receiving nodes 130-150) which group(s) (e.g., the group 160) the receiving nodes 130-150 are associated with. Some examples of multicast control protocols are IGMP, Protocol-Independent Multicast (PIM), Real-Time Streaming Protocol (RTSP), Multiprotocol Border Gateway Protocol (MBGP), Multicast Source Discovery Protocol (MSDP), Simple Service Discovery Protocol (SSDP), and Source Specific Multicast (SSM). For example, the receiving node 130 may send a multicast control protocol packet to the access point 120 to change the channel for an IPTV multicast stream received from the source node 110. The multicast control protocol packet informs the access point 120 that the receiving node 130 is interested in receiving group packets for the selected channel.

0025The access point 120 of some embodiments is further configured to maintain information about "associated nodes." Associated nodes are devices that have negotiated a wireless communication link (e.g., the wireless link 135) with the access point 120. For example, when the receiving node 130 initially associates with the access point 120 to negotiate the wireless link 135, the receiving node 130 provides a Media Access Control (MAC) or hardware address that uniquely identifies the receiving node 130. The receiving node 130 may also provide a list of allowable physical data rates (e.g., 1 Mbps - 54 Mbps) at which it may communicate with the access point 120. The access point 120 may store such information about the associated nodes in memory, for example.

0026As described further herein, the system 100 improves multicast data throughput in the wireless LAN because the access point 120 of one embodiment is configured to convert the multicast packet addressed to the group 160 into one or more unicast packets addressed to the receiving nodes 130-140. The access point 120 may transmit the one or more unicast packets sequentially to the receiving nodes 130-140 at a higher data rate than the minimum data rate used for 802.11 multicast transmission. Further, the access point 120 of this embodiment would ensure reliable transmission of the converted multicast packet because the access point 120 would be able to service 802.11 ACK packets generated by the receiving nodes 130-140. In some embodiments, the access point 120 may determine not to convert the multicast packet into one or more unicast packets, but instead may transmit the multicast packet to the receiving nodes of the group 160 at a relatively higher data rate than the minimum allowable physical data rate used for 802.11 multicast packet transmission.

0027<figref idref="f0002">FIG. 2</figref> illustrates an exemplary method for multicast or unicast transmission in the wireless local area network of <figref idref="f0001">FIG. 1</figref>, in accordance with one embodiment of the present invention. The steps of the exemplary method are described as occurring in particular order, but it will be appreciated that certain steps may be rearranged to provide a similar result. The method determines whether to convert a multicast packet into one or more unicast packets or whether to transmit the multicast packet. The method also determines at what rate to transmit the multicast packet and the one or more unicast packets. The method begins with the access point 120 already associated with receiving nodes 130-150.

0028In step 205, the access point 120 receives a first join request (e.g., a multicast control protocol packet such as an IGMP join request) from the first receiving node (e.g., the receiving node 130) containing a first address for the receiving node 130. The access point 120 uses the join request to correlate the receiving node 130 with the address of the group 160. In IGMP, a multicast client (e.g., the receiving node 130) joins a multicast group (e.g., the group 160) to enable group reception of a multicast traffic stream. When the access point 120 receives the IGMP join request from the receiving node 130, the access point 120 inspects the IGMP packet and determines the required join information.

0029In this embodiment, the access point 120 does not itself use the IGMP protocol. Regardless, the system 100 takes advantage of the fact that the IGMP join requests from the receiving nodes 130-140 to the source node 110 pass through the access point 120. The access point 120 "sniffs" or samples the IGMP join requests to map the hardware (MAC) address of the receiving nodes 130 and 140 with the address of the group 160. In some embodiments, the access point 120 "speaks" the IGMP protocol. The access point 120 may map the IP addresses (instead of the MAC addresses) of the receiving nodes 130 and 140 to the address of the group 160.

0030In the alternative to sniffing or speaking IGMP or other control protocols from the receiving nodes 130-150, the access point 120 may maintain a map that contains the hardware addresses of all or a subset of the receiving nodes 130-150 that are associated with the access point 120. The access point 120 may use the map to query the receiving nodes 130-150 to determine which of the receiving nodes 130-150 are interested in receiving multicast traffic addressed to the group 160. These maps of MAC addresses or IP addresses allow the access point 120 to convert the multicast packet received from the source node 110 and addressed to the group 160 into one or more unicast packets addressed to the receiving nodes 130-140 of the group 160.

0031In step 210, the access point 120 maps the first address of the receiving node 130 from the IGMP packet to the address of the group 160. In step 215, the access point 120 receives a second join request (e.g., a second IGMP join request) from a second receiving node (e.g., the receiving node 140). In step 220, the access point 120 maps a second address of the receiving node 140 to the address of the group 160.

0032In step 225, the access point 120 receives the multicast packet addressed to the group 160. In step 230, the access point 120 determines a first data rate (e.g., 54 Mbps) by which the access point 120 may reliably transmit (e.g., including the 802.11 ACK mechanism) one or more unicast packets to the receiving node 130. In step 235, the access point 120 determines a second data rate (e.g., 24 Mbps) by which the access point 120 may reliably transmit one or more unicast packets to the receiving node 140. Although not depicted, in some embodiments the access point 120 may determine additional (e.g., a third or more) data rates by which the access point 120 may reliably transmit one or more unicast packets to a third receiving node (e.g., the receiving node 150 which would be part of the group 160).

0033In step 240, the access point 120 determines an effective unicast rate. As discussed further with respect to <figref idref="f0003">FIG. 3</figref>, the effective unicast rate corresponds to a combined rate for converting the multicast packet into one or more unicast packets and sending the one or more unicast packets to the receiving nodes 130 and 140 of the group 160 at the first and second (and third...) data rates. The effective unicast rate depends on the total number of bits included in the unicast packets, including additional data packet overhead (e.g., additional bits in the unicast packet as compared to the multicast packet). The effective unicast rate also depends on computational time associated with converting the multicast packet into one or more unicast packets. The effective unicast rate is further based on the duration for reception and processing of ACK packets from the receiving nodes of the group 160. Further, the effective unicast rate is based on the number of receiving nodes in the group 160, because each additional receiving node in the group 160 proportionally lowers the effective unicast rate. One method for determining the effective unicast rate is presented in co-pending U.S. Patent Application entitled "System and Method for Transmission Parameter Control for an Antenna Apparatus with Selectable Elements.

0034As described further, rather than converting the multicast packet to unicast packets, the access point may transmit at a "lowest common denominator rate" to the group 160. For example, the lowest common denominator rate may be higher than the effective unicast rate, particularly with a large number of receiving nodes in the group 160 each receiving at a relatively high rate. For example, the group 160 may comprise the receiving nodes 130, 140, and 150. The receiving node 130 may receive packets at a physical data rate of 54 Mbps, the receiving node 140 may receive packets at a physical data rate of 54 Mbps, and the receiving node 150 may receive packets at a physical data rate of 54 Mbps. The lowest common denominator rate for this example is 54 Mbps, which may be higher than the effective unicast rate. In step 245, the access point 120 determines the lowest common denominator rate (LCDR) for transmitting the multicast packet simultaneously to the receiving nodes of the group 160.

0035In steps 250-295, the access point 120 determines whether to transmit unicast or multicast packets, and at what rate to transmit the unicast or multicast packets. Specifically, in steps 250-275, the access point 120 may determine to convert the multicast packet into one or more first unicast packets addressed to the receiving node 130 and one or more second unicast packet addressed to the receiving node 140 for transmission. Alternatively, in steps 285-295, the access point 120 may determine to transmit the multicast packet simultaneously to the receiving nodes 130-140 of the group 160 and not convert the multicast packet into unicast packets. Further, in steps 285-295 the access point 120 determines whether to transmit at the lowest common denominator rate if the lowest common denominator rate is higher than the minimum allowable physical data rate.

0036In step 250, the access point 120 determines if the effective unicast rate exceeds the lowest common denominator rate. For example, in an 802.11a wireless LAN with the receiving nodes 130, 140, and 150 in the group 160, the first data rate may be 54 Mbps, the second data rate may be 6 Mbps, and the third data rate may be 54 Mbps. The effective unicast rate, given the number of data bits in the unicast packets, packet overhead, conversion processing time, and the like may be 11.5 Mbps, for example. Accordingly, the effective unicast rate of 11.5 Mbps exceeds the lowest common denominator rate of 6 Mbps (i.e., the minimum allowable physical data rate for 802.11a), so the access point 120 will convert the multicast packet into one or more unicast packets in steps 255-275.

0037In step 255, the access point 120 converts the multicast packet to a first unicast packet addressed to the receiving node 130. In step 260, the access point 120 transmits the first unicast packet to the receiving node 130 at the first data rate. After transmission of the first unicast packet, in step 265 the access point 120 may delay for a predetermined delay period before converting the multicast packet into a second unicast packet and transmitting the second unicast packet to the receiving node 140 in steps 270-275. The delay period is computed to allow the receiving node 130 sufficient time to generate an 802.11 ACK that the access point 120 may receive to verify reliable transmission and reception of the first unicast packet. The access point 120 may compute the delay period based on several factors. For example, the access point 120 may compute the delay based on computational time needed by the access point 120 to convert the multicast packet into the first unicast packet. The delay may include data packet overhead (e.g., additional bits in the first unicast packet that reduce the first data rate to a relatively lower "user" data rate). Further, the access point 120 may retransmit the first unicast packet to the receiving node 130 if the access point 120 does not receive the 802.11 ACK from the receiving node 130 for the first unicast packet, adding to the delay.

0038In step 270, the access point 120 converts the multicast packet from the source node 110 into a second unicast packet addressed to the receiving node 140. In step 275, the access point 120 transmits the second unicast packet at the second data rate to the receiving node 140. In similar fashion to the method described above with respect to steps 260-265 for the first unicast packet, the access point 120 awaits an 802.11 ACK from the receiving node 140 to ensure reliable transmission and reception of the second unicast packet. The access point 120 may retransmit the second unicast packet to the receiving node 140 if the access point 120 does not receive the 802.11 ACK from the receiving node 140. Although not depicted, the steps 265 to 275 may be repeated for additional (e.g., third...) receiving nodes in the group 160.

0039Optionally, the access point 120 may determine in step 260 and step 275 whether one of the receiving nodes of the group 160 comprises a multicast data transmitter. For example, if the receiving node 130 acts as the source node 110 for sending the multicast packet through the access point 120 to the receiving nodes 140 and 150 of the group 160, the access point 120 need not retransmit the converted unicast packet back to the receiving node 130. Although sending the unicast packet back to the receiving node 130 is legitimate practice in 802.11, doing so wastes network bandwidth.

0040At step 250, if the effective unicast rate does not exceed the lowest common denominator rate, the access point 120 may determine not to convert the multicast packet into one or more unicast packets for sequential transmission to each receiving node in the group 160. Accordingly, in step 285, the access point 120 determines whether the LCDR exceeds the minimum allowable data rate. For example, if the receiving node 130 is capable of receiving at 54 Mbps and the receiving node 140 is capable of receiving at 24 Mbps, the LCDR of 24 Mbps exceeds the minimum allowable data rate of 6 Mbps. Accordingly, in step 290 the access point 120 will transmit the multicast packet to the group 160 at the LCDR of 24 Mbps. Alternatively, at step 285 if the receiving node 130 is capable of receiving at 54 Mbps and the receiving node 140 is capable of receiving at only 6 Mbps, for example, the LCDR does not exceed the minimum allowable data rate of 6 Mbps. Accordingly, in step 295, the access point 120 will transmit the multicast packet to the group 160 at the minimum allowable data rate of 6 Mbps.

0041The methods described with respect to <figref idref="f0002">FIG. 2</figref> advantageously achieve higher data throughput than traditional multicast transmission, by converting multicast packets in the access point 120 into one or more unicast packets that may be transmitted sequentially to each receiving node of the group 160 at a relatively higher data rate. Further, converting the multicast packet into unicast packets affords higher data transmission reliability because the unicast packets are verified by ACK responses from each receiving node of the group 160. Additionally, if the access point 120 determines not to convert multicast packets into unicast packets, the access point 120 may transmit the multicast packet at the lowest common denominator rate, which is a higher physical data rate than the minimum allowable physical data rate defined in the IEEE 802.11 standard.

0042Although <figref idref="f0001">FIGS. 1</figref> and <figref idref="f0002">2</figref> generally describe multicast data flow from the source node 110 to the group 160 (i.e., left to right in <figref idref="f0001">FIG. 1</figref>), the methods described with respect to <figref idref="f0002">FIG. 2</figref> are applicable to multicast control protocol packets that flow in the opposite direction (e.g., from right to left in <figref idref="f0001">FIG. 1</figref>). For example, the system 100 may include a source node (e.g., the receiving node 130) configured to transmit a group packet to a destination node (e.g., the access point 120). The receiving node 130 sends a multicast control protocol packet, such as an IGMP join request, over the wireless link 135 to the access point 120 to join a group (e.g., group 160) receiving an IPTV multimedia multicast stream. To provide more effective use of the available bandwidth of the wireless link 135, and to provide reliable transmission of the multicast control protocol packet, the receiving node 135 may convert the multicast control protocol packet to one or more unicast packets for transmission to and acknowledgement by the access point 120.

0043In one example, the receiving node 130 determines a first data rate for transmitting the group packet and determines a second data rate based upon converting the group packet to a unicast packet addressed to the access point 120. The receiving node 130 transmits the unicast packet at the second data rate through the wireless link 135 to the access point 120 if the first data rate for transmitting the group packet is less than the second data rate for transmitting the unicast packet. As discussed herein, the receiving node 130 transmits the unicast packet at a higher physical data rate than specified for multicast transmission. Upon receipt of the unicast packet, the access point 120 sends an ACK to acknowledge receipt of the unicast packet.

0044If the first data rate for transmitting the group packet is greater than the second data rate for transmitting the unicast packet, the receiving node 130 may transmit the group packet through the wireless link 135. As previously discussed, the receiving node 130 may transmit the group packet at the lowest common denominator rate. The access point 120 then receives the group packet and processes the multicast control protocol packet. Therefore, in these embodiments, the receiving node 130 and the access point 120 individually determine whether transmitting the group packet or converting the group packet to one or more unicast packets allows more effective use of the available bandwidth and reliable transmission.

0045<figref idref="f0003">FIG. 3</figref> illustrates an exemplary timing diagram comparing the conversion of the multicast packet into one or more unicast packets, as described in <figref idref="f0001 f0002">FIGS. 1-2</figref>, as compared to multicast packet transmission, in accordance with one embodiment of the present invention. A first time interval 310 indicates the time needed for the access point 120 to convert the multicast packet received from the source node 110 into the first unicast packet and transmit the first unicast packet to the receiving node 130, for example, at 54 Mbps. It will be appreciated that the time interval 310 may vary depending upon at least the first data rate, the number of data bits in the first unicast packet, and the conversion time needed by the access point 120 to convert the multicast packet into the first unicast packet. After the first unicast packet is transmitted to the receiving node 130, an ACK time interval 320 indicates the time needed for the receiving node 130 to return the 802.11 ACK corresponding to the first unicast packet and for the access point 120 to process the 802.11 ACK packet.

0046Similarly, a second time interval 330 indicates the time needed for the access point 120 to convert the multicast packet received from the source node 110 into the second unicast packet and transmit the second unicast packet to the receiving node 140 at the second data rate, for example, 18 Mbps. A second ACK time interval 340 indicates the time needed for the receiving node 140 to return an 802.11 ACK corresponding to the second unicast packet and for the access point 120 to process the 802.11 ACK packet. In comparison, a multicast time interval 350 indicates the duration for the access point 120 to receive and transmit the multicast packet simultaneously to the receiving nodes 130 and 140 at either the lowest common denominator rate or the minimum allowable physical data rate.

0047Because the duration of the combined time intervals 310, 320, 330, and 340 is shorter than the duration of the multicast time interval 350, the system and method described herein advantageously achieve a higher data throughput by converting the multicast packet to sequential unicast packets. Further, as the duration of the time intervals 310 and 320 increases because of interference in the wireless links 135 and 145 (<figref idref="f0001">FIG. 1</figref>) leading to lower first and second data rates, for example, the combined duration of the time intervals 310, 320, 330, and 340 may exceed the multicast time interval 350. In such case, the lowest common denominator rate may provide a higher data rate than the minimum allowable data rate. Another advantage, therefore, is graceful degradation of the overall data transmission rate with changes in the wireless LAN.

0048The embodiments discussed herein are illustrative of one example of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications or adaptations of the methods and/or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims.