Abstract:
Each of a plurality of nodes in a wireless network is capable of generating, transmitting, and receiving beacons in a distribute fashion. Each beacon contains information regarding the order of which other nodes are to transmit beacons and wireless medium access information at to when various nodes are to access the network. Nodes that are in separate “extended neighborhoods” are permitted to transmit their beacons simultaneously without risking beacon collisions. The beacons contain information that is used to ensure this result. Using the distributed beacon mechanism, each nod can reserve access to the wireless medium. In the disclosed embodiments, a central coordinator is not needed.

Description:
RELATED APPLICATONS 
     This application claims priority to the following Provisional Patent Applications, both of which are incorporated herein by reference: Appl. No. 60/542,170 entitled “Adaptive Beacon Circulation for Medium Access Control,” filed Feb. 5, 2004 and Appl. No. 60/542,338 entitled “Medium Access Control Via Adaptive Beacon Coordination,” filed Feb. 6, 2004. 
    
    
     BACKGROUND 
     In a wireless communication network, two or more wireless-capable devices (e.g., computers) communicate with one another over a wireless medium. Most wireless networks include a provision to coordinate access to the wireless medium in an attempt to avoid message “collisions” in which two or more messages are received simultaneously thereby interfering with each other. In some networks, one or more of the nodes serves as a central coordinator to coordinate access to the wireless medium on the part of the other nodes. While generally satisfactory, this approach suffers if the central coordinator moves out of range of one or more of the other nodes. Being out of range could result if the central coordinate is a mobile device and is moved away relative to the other nodes, or if one or more of the other nodes is mobile and is moved away relative to the central coordinator. A wireless medium access coordination scheme that addresses this issue is desirable, particularly one that permits faster, more efficient access to the wireless medium. 
     SUMMARY 
     Various embodiments are described herein of a wireless network capable in which each of a plurality of nodes generates and transmits beacons in a distributed fashion. Each beacon contains information regarding the order of which other nodes are to transmit beacons and wireless medium access information as to when various nodes are to access the network. Nodes that are in separate “extended neighborhoods” are permitted to transmit their beacons simultaneously without risking beacon collisions. The beacons contain information that is used to ensure this result. Using the distributed beacon mechanism, each node can reserve access to the wireless medium. In the disclosed embodiments, a central coordinator is not needed. 
     In accordance with at least one embodiment, a method is disclosed that is implemented in a wireless communication network comprising a plurality of nodes that communicate across a wireless medium. The method comprises a first node receiving a first beacon from a second node. The beacon identifies a node within communication range of the second node. The first node generates a second beacon based on the first beacon. The second beacon specifies an order of nodes that are to transmit beacons and, for each such node, whether that node is within wireless communication range of the first node. 
     In accordance with another embodiment of the invention, a method (and associated method) comprises generating a wireless medium access change beacon that contains a reservation request to reserve access to the wireless medium. The method also comprises transmitting the beacon across the wireless medium and implementing the reservation request after other nodes receive the wireless medium access change beacon. 
     In other disclosed embodiments, a node, operable in a wireless network, comprises host logic and a wireless transceiver coupled to the host logic. The wireless transceiver receives a first beacon from a transmitting device. The first beacon is configured to identify another device that is within communication range of the transmitting device. The host logic generates a second beacon based on the first beacon. The second beacon specifies an order of devices that are to transmit beacons and, for each such device, whether that device is within communication range of the node. 
     In yet another embodiment, a node comprises host logic and e wireless transceiver. The host logic causes the wireless transceiver to generate a wireless medium access change beacon that contains a reservation request to reserve access to the wireless medium. The wireless transceiver receives a wireless medium access change beacon from another node. The received wireless medium access change beacon also contains a reservation request to reserve access to the wireless medium. 
     In yet another embodiment, a system comprises a plurality of wireless communication devices. Each wireless communication device is capable of transmitting beacons and receiving beacons and is capable of communicating with at least one other wireless communication device. Each wireless communication device transmits a beacon that encodes which other devices are within wireless communication range of that device. In this embodiment, at least two wireless communication devices transmit beacons simultaneously. 
     Another embodiment is directed to a system that comprises a plurality of wireless communication devices. Each wireless communication device is capable of communicating with at least one other wireless communication device. Each wireless communication device is capable of transmitting a request to reserve wireless medium access. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  shows a wireless communication network comprising a plurality of nodes; 
         FIG. 2  shows an embodiment of a node; 
         FIG. 3  illustrates the “extended neighborhood” of a node; 
         FIG. 4  illustrates a method embodiment; 
         FIG. 5  illustrates that two or more nodes can transmit their beacons concurrently; 
         FIGS. 6A-6E  illustrate an embodiment of a beacon frame in accordance with a preferred embodiment of the invention; and 
         FIG. 7  shows another method embodiment. 
     
    
    
     NOTATION AND NOMENCLATURE 
     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. The term “system” refers to a combination of two or more components and may be used in any one of a variety of contexts such as a communication system, a sub-system of a communication device, a system of wireless nodes, etc. The term “piconet” refers to a network of two or more wireless devices. 
     DETAILED DESCRIPTION 
     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Referring now to  FIG. 1 , a wireless communication network is shown comprising two or more nodes. In the exemplary wireless communication network of  FIG. 1 , the network comprises nodes labeled as node  1 , node  3 , node  4 , node  6 , node  9 , node  12 , node  14 , node  19 , node  22 , and node  30 . Each node in the network is capable of wirelessly communicating with one or more other nodes in the network. The lines  50  interconnecting the various nodes depict the possible communication paths within the network. For example, node  1  is within wireless communication range of nodes  3 ,  4 ,  12 , and  19  and thus is shown interconnected to those nodes in  FIG. 1  by way of four connection lines  50 . By way of further example, node  6  is connected by two lines  50  to nodes  9  and  19  to indicate that node  6  is within communication range of nodes  9  and  19 . Node  6 , however, is not shown as being connected to any of the other nodes in the network, thereby indicating that node  6  is not within communication range of such other nodes. For example, node  6  is not within radio range of node  12 . Two nodes that are within direct wireless communication range of each other are said to be “immediate neighbors.” 
     In accordance with a preferred embodiment of the invention, each node is capable of transmitting a “beacon” message frame. A beacon is received by any node within communication range of the node that transmits the beacon. In general, beacons are used to coordinate access to the wireless medium among the various nodes in the network. Each node becomes aware of the existence of its immediate neighbors based on receiving a beacon from each such neighbor. The use and format of a beacon will be further described in detail below. 
     Each node in the network can be any type of wireless-enabled communication device such as a computer, a personal data assistant (PDA), and the like.  FIG. 2  shows an exemplary embodiment of a typical node as comprising host logic  100  coupled to a transceiver  102 . An antenna  104  is connected to the transceiver  102  to provide wireless communication (e.g., radio communication) to other nodes in the network. The transceiver  102  is capable both of transmitting data to and receiving data from other nodes. As such, the communication links between nodes generally comprises a bi-directional communication path. The host logic performs various functions specific to the node. If the node was a computer, for example, the host logic  100  would include the computer&#39;s processor, memory, etc. 
     It can be observed from  FIG. 1  that a node can be within communication range of one or more other nodes, but out of communication range from still other nodes. The group of nodes that are outside the communication range of a particular node fall into two categories. In a first category are nodes that are within communication range of a node that itself is within communication range of the particular node. For example, nodes  1 ,  3 ,  4 , and  14  are outside the communication range of node  6  but are within communication range of either or both of nodes  9  and  19  which are themselves within communication range of node  6 . 
     A second category of “out of communication range” nodes are those nodes that are not even within communication range of a node that is within radio range of a given node. Referring to the example of  FIG. 1  again, this latter category of nodes comprises nodes  12 ,  22 , and  30 . Nodes  12 ,  22 , and  30  are not within communication range of a node that is within communication range of node  6 . For example, node  12  is within communication range of nodes  1 ,  3 , and  4 , but none of nodes  1 ,  3 , and  4  are themselves within communication range of node  6 . 
     Based on the groupings of nodes as discussed above, the concept of an “extended neighborhood” can be defined for each node in a communication network. Referring now to  FIG. 3 , the communication network of  FIG. 1  has been redrawn, this time with a dashed line  110  encircling nodes  1 ,  3 ,  4 ,  6 ,  9 ,  14 , and  19 . Dashed line  110  encircles those nodes that comprise the extended neighborhood of node  6 . As such, the extended neighborhood  110  of node  6  comprises nodes  9  and  19  that are within direct communication range of node  6 , as well as nodes  1 ,  3 ,  4 , and  14  that, while not within direct communication range of node  6 , are still within communication range of a node (nodes  9 ,  19 ) that is within direct communication range of node  6 . In the example of  FIG. 3 , the extended neighborhood  110  of node  6  specifically excludes nodes  12 ,  22 , and  30  which are, as described above, not within communication range of node  6  or within communication range of a node that is within communication range of node  6 . 
     The concept of an extended neighborhood can be used to implement an efficient wireless medium access protocol as described herein. In accordance with a preferred embodiment of the invention, each node in the wireless communication network is capable of transmitting a beacon. Accordingly, each node is capable of receiving beacons from other nodes within wireless communication range of that node. The beacons can be used to convey neighborhood information in accordance with various embodiments of the invention as illustrated below. As a result of this distributed transmission of beacons through the network, two or more nodes outside an extended neighborhood of one of the nodes may transmit their beacons simultaneously without repercussion of a collision. 
       FIG. 4  illustrates a method embodiment comprising actions  130  and  132 . The method of  FIG. 4  preferably is performed independently by each node in the network. At  130 , the method comprises receiving a beacon from another node. Preferably, the beacon received identifies one or more nodes that are within communication range of the node that transmitted that beacon. The received beacon also specifies the order for which other nodes are to transmit beacons. The preferred format for the beacon message (also called a “frame”) will be discussed below with respect to  FIGS. 6A-6E . At  132 , the node that receives the beacon generates its own beacon based on information contained in the received beacon. The generated beacon specifies nodes that are to transmit future beacons. Further, the generated beacon may also include immediate neighborhood information of the node generating the beacon. For example, a beacon generated by node  19  (see  FIG. 1 ) would include the identity of nodes  1 ,  4 ,  6 ,  9 , and  14  that are within direct communication range of node  19 . Any node that receives the beacon from node  19  will thus be informed that nodes  1 ,  4 ,  6 ,  9 , and  14  are within direct communication range of node  19 . Node  6 , for example, will be informed that node  1  is within range of node  19 . 
     As explained above, each node becomes aware of the existence of its immediate neighbors based on receiving a beacon from each such neighbor. By receiving beacons from nodes  1 ,  4 ,  6 ,  9 , and  14 , node  19  becomes aware of the existence of those neighbor nodes. By receiving beacons from nodes  9  and  19 , node  6  is made aware that nodes  9  and  19  are immediate neighbors of node  6 . Further, the beacons transmitted by nodes  9  and  19  identify the immediate neighbors of nodes  9  and  19 . Armed with this neighborhood information, node  6  will be aware of its own neighbors and the neighbors of its neighbors (node  6 &#39;s extended neighborhood). Alternatively stated, node  6  will be aware of its own neighbors, nodes  9  and  19 , as well as its neighbor&#39;s immediate neighbors, nodes  1 ,  3 ,  4 , and  14 . Nodes that are within the same extended neighborhood should not transmit beacons simultaneously to avoid collisions. Nodes that are not within the same extended neighborhood (e.g., nodes  6  and  12 ) can transmit beacons simultaneously because their spatial separation avoids or reduces the potential for collisions. Accordingly, each node need only be aware of the identity of the nodes in its extended neighborhood. The beacons described herein convey sufficient information by which each node can be made aware of its extended neighborhood. A preferred beacon frame format is described below with regard to  FIG. 6A-6E . 
       FIG. 5  illustrates a time sequence of beacons comprising beacon  11  through beacon  17  transmitted in order one after the other. The time between beacons, denoted by reference numeral  120  comprises time in which one or more nodes may access the wireless medium to transmit data. Each beacon preferably coordinates the access to the wireless medium during the time period  120  immediately following that beacon. The time from one beacon to next, designated with reference numeral  121 , is referred to as the “beacon interval.” As can be seen in the example of  FIGS. 1 and 5 , nodes  6  and  12  as well as nodes  19  and  30  are permitted to transmit their beacons simultaneously. This results from the fact that node  12  and  30  are not within the extended neighborhood of node  6  and  19 , respectively. Because no node is within direct communication range of nodes  6  and  12 , the potential for a collision due to the simultaneous transmission of beacons from nodes  6  and  12  is avoided or at least greatly reduced. The same is true regarding nodes  19  and  30 . 
     In accordance with the preferred embodiment, each node is capable of generating and transmitting a beacon. A beacon contains a variety of information such as the order of which nodes are to transmit future beacons and reservation information as to which nodes are granted access to the wireless medium at specified points in time, etc. A beacon may also contain new information not previously known to other nodes. For example, a node may have a need to reserve access to the wireless medium for communications with other nodes. Such a node may generate an “access change” beacon that contains the new information (e.g., the new reservation request). Based on the beacons previously received, the node will already know the extent of the wireless medium availability and can submit a request for medium access change accordingly. The distributed nature of the beacons then disseminates the new reservation request to other nodes so that such other nodes are made aware of and comply with the new reservation request. Other types of access changes can also be implemented in an access change beacon such as an altered order for the nodes that are to transmit beacons in the future. The identification as to whether a beacon is an access change beacon may be encoded in a beacon header that accompanies the beacon payload. 
     The preferred format of a beacon frame will be illustrated below with respect to  FIGS. 6A through 6E . The illustrated beacon format is applicable for beacons and access change frames as well. Referring to  FIG. 6A , a preferred embodiment of a beacon frame payload is illustrated as comprising a plurality of fields. Such fields include a beacon primary field  150 , a static medium access information element (IE)  152 , a dynamic medium access IE  154 , a dynamic node order IE  156 , a static node order IE  158 , a node capability IE  160 , and one or more other IEs  162  if desired.  FIG. 6B  illustrates a preferred embodiment of the beacon primary field  150 . As shown, the beacon primary field  150  comprises a beacon counter  164 , a beacon interval  166 , a beacon set ID  168 , a beacon transmitter address  170 , a beacon countdown value  172  and a reserved field  174 . The beacon counter  164  specifies a unique, preferably sequential number associated with the beacon containing this parameter. The beacon counter is incremented by one for each beacon to be transmitted at the next target beacon transmit time (TBTT). The TBTT is the time at which a particular beacon is scheduled to be transmitted. Each node that is to transmit a beacon generates the beacon counter by incrementing the beacon counter in the last received beacon. The beacon counters of the beacons illustrated in  FIG. 5  are the numerals  11  through  17 . 
     Referring still to  FIG. 6B , the beacon interval  166  specifies the length of the interval, in units of microseconds, between the current TBTT and the next TBTT (time period  121  in  FIG. 5 ). The beacon set ID  168  identifies the set of beacons transmitted by the device. The beacon transmitter address  170  specifies the address of the node sending the beacon referenced in the beacon counter  164 . The beacon countdown value  172  specifies the number of beacon intervals before an access change, if any, specified in the current frame (if the frame contains new or modified access change information) takes effect. The beacon countdown value may initially be set to a NumCountdownlnitial (NCI) value and then decremented by one in each successive beacon until reaching the value of zero. The value of zero for the beacon countdown indicates that the change is to take effect in the current beacon interval or took effect since an earlier beacon interval, while a value of one indicates that the change is to take effect in the subsequent beacon interval. A change may be made when another change is yet to take place, that is, when the beacon countdown value is nonzero, by resetting the beacon countdown to the NCI value. The beacon interval  166  and beacon set ID  168  may be changed via the access change frames. 
       FIG. 6C  shows a preferred embodiment of the static medium access IE  152  and the dynamic medium access IE  154 . The static medium access IE  152  includes an IE ID  176 , a length value  178 , and one or more access intervals  180 . The IE ID field  176  comprises an identifier that identifies the information element as the static medium access IE. The length value  178  specifies the length of the field that follows this length field in this static medium access IE; from the length value the number of access intervals  180  can be determined by nodes receiving the beacon. Each access interval comprises a format such as that shown in  FIG. 6C  as including a sending node ID  188 , a recipient node ID  190 , an access start value  192 , and an access end value  194 . Each access interval  180  specifies a time interval for wireless medium access that is valid in each beacon interval following the beacon in which the beacon countdown  172  is set to zero. The sending node ID  188  identifies the node that is permitted to transmit in the associated time interval. In some embodiments, the sending node ID  188  may be encoded as a broadcast node ID or a multicast node ID which means that all of the nodes (for a broadcast situation) or the nodes associated with the multicast node ID (for a multicast situation) may transmit in this time interval based on a suitable contention algorithm (e.g., a binary backoff carrier sense multiple access (“CSMA”) algorithm). The recipient node ID  190  identifies the node required to receive in this time interval. If the recipient node ID is set to the broadcast node ID or a multicast node ID, all of the active nodes or the active nodes associated with the multicast node ID are potential intended recipients in this time interval. 
     The access start value  192  specifies the start time, preferably in units of microseconds, of this access time interval relative to the TBTT that begins the beacon interval in which this time interval is located. A value of zero for the access start value  192  indicates that this time interval may start in this beacon interval anywhere outside the beacon and the other time intervals specified in the static medium access IE  152  and dynamic medium access IE  154  contained in this beacon or previous beacons. The access end value  194  specifies the end time, in units of microseconds, of this time interval relative to the TBTT beginning the beacon interval in which this time interval is located. As with the start value  192 , a value of zero indicates that this time interval may end in this beacon interval anywhere outside the beacon and the other time intervals specified in the applicable static medium access IE and dynamic medium access IE contained in this or previous frames. 
       FIG. 6C  also shows the format of the dynamic medium access IE  154  comprising an IE ID  182 , a length value  184 , one or more beacon offset values  186  and an access interval  180  associated with each beacon offset  186 . The format of each such access interval  180  is also shown in  FIG. 6C  and was discussed above. The IE ID field  182  comprises a value that identifies that information element as the dynamic medium access IE. The length field  184  specifies the length of the field that follows this length field in this dynamic medium access IE  154  and thereby defines the number of beacon offset and access interval pairs contained within the information element  154 . Each beacon offset  186  is paired with the subsequent access interval  180  and specifies a beacon interval, relative to the current beacon interval, to which the paired access interval applies. A value of zero for the beacon offset  186  indicates that the paired access interval  180  is valid in the current beacon interval, while a value of one indicates that the paired access interval is valid in the next beacon interval, and so on. Each access interval  180  in the dynamic medium access IE  154  is paired with the preceding beacon offset and specifies a time interval for medium access that is valid only in the beacon interval referenced in that beacon offset relative to the beacon counter  164 . 
     The format of the dynamic node order and static node order IEs  156  and  158  is as shown in  FIG. 6D  and includes an IE ID  196 , a length value  198 , one or more node IDs  200 , and a node status  202  associated with each node ID  200 . The IE ID  196  comprises a value that defines the information element as either a dynamic node order IE  156  or a static node order IE  158 . The length value  198  defines the length of the field that follows this length field in this IE  156 ,  158 . Based on the length value  198 , the number of node ID and node status pairs  200 ,  202  can be determined. 
     Each node ID  200  is paired with a subsequent node status  202  and identifies a node that is scheduled to transmit a beacon after the current beacon. The first node ID following the length value  198  identifies the node that is scheduled to transmit a beacon at the next TBTT. Each successive node ID  200  identifies the node scheduled to transmit a beacon at each successive TBTT, provided the spatial reuse bit  204  (discussed below) in the paired node status field is set to zero. A node ID  200  with the corresponding spatial reuse bit  204  set to a value of one identifies the node scheduled to transmit a beacon at the same TBTT as the node identified in the preceding node ID field  200 . The same node ID value may appear more than once in either information element  156  or  158 , indicating that the corresponding node may transmit a beacon more than once in the set of beacons scheduled to be transmitted by the nodes specified in that IE. The node ID fields  200  thus define the order of nodes that are to transmit future beacons. The nodes listed in IE  156 ,  158  are the nodes that are in the extended neighborhood of the node transmitting the current beacon. 
     Each node status  202  is paired with the preceding node ID  200  and further contains the parameters also shown in  FIG. 6D . In accordance with the preferred embodiment, such parameters include a spatial reuse bit  204 , an in-range bit  206 , a missed beacons field  208  and a reserved field  210 . The spatial reuse bit  204  specifies whether the node identified in the paired node ID field  200  is scheduled to transmit a beacon at the same TBTT as the node identified in the previous node ID. The in-range bit  206  indicates whether the node identified in the paired node ID field  200  is in communication range of the node transmitting the present beacon frame. If the node identified in the paired node ID field is in communication range of the node transmitting the beacon, then the associated in-range bit  206  is set to one to so indicate. If, however, the node identified in the paired node ID field is not within communication range of the node transmitting the current beacon, the associated in range bit  206  is set to a value of zero. The missed beacons filed  208  indicates the number of the latest, consecutive beacons that were expected from the node identified in the paired node ID field  200 , but were not received by the node transmitting the current beacon. 
     The dynamic node order IE  156  specifies a list of nodes that will be transmitting a beacon following the listed order without repeating the list. The static node order IE  158  specifies a list of nodes that will be transmitting a beacon following the listed order. The listed order of the static node order IE is repeated. 
       FIG. 6E  illustrates the definition of the node capability IE  160 . As shown, the node capability IE  160  includes an IE ID  212 , a length  214 , a node state  216 , a supported physical layer (PHY)  218 , and maximum medium access control (“MAC”) service data unit (“MSDU”) size  220 , and a reserved field  222 . The IE ID  212  is encoded to specify that the current IE is the node capability IE  160  and the length value  214  defines the length of the field that follows this length field in this node capability IE  160 . The node state  216  is also illustrated in  FIG. 6E  as including an activation field  224 , a reception field  226 , a power supply field  228 , and a reserved field  230 . The activation field  224  preferably comprises two bits that are encoded to indicate the current state of the node transmitting the beacon. With two bits, the activation field  224  can encode four different states including the “active” state, the “becoming active” state, the “becoming inactive” state, and the “becoming active with another piconet” state. The active state refers to a case where the node is constantly ready to transmit and receive frames. The becoming active state refers to a case where the node is becoming ready to transmit and receive frames. The becoming inactive state refers to a case where the node will not be ready to transmit and receive frames. The becoming active with another piconet refers to a case where the node will be ready to transmit and receive frames belonging to a different piconet but not to the current piconet. The reception field  226  preferably includes three bits to encode as many as eight different scenarios in which the node transmitting the beacon will be receiving frames. The reception field  226  encodes whether the node transmitting the beacon will be receiving frames 1) always (outside its own transmission time), 2) outside time intervals reserved for CSMA-based contention, 3) in time intervals reserved for CSMA-based contention, 4) in time intervals for which this node is specified as a recipient, and 5) in time intervals for which the node specified as the sender of any time intervals with this node specified as the recipient is specified as the sender. Three additional encodings of the reception field  226  are reserved. 
     The power supply field  228  preferably comprises two bits that are encoded to indicate the current power level of the node transmitting the beacon. The power supply bits can be encoded to indicate a low battery level, a mid-battery level, a high battery level, and a power connection to an alternating current (AC) power source. The supported PHY field  218  of the node capability IE  160  contains a supported data rates field  232 , a supported bands field  234 , and a reserved field  236 . The supported data rates field  232  indicates the data rates supported by the node transmitting this frame and may be encoded as the same as in the PHY header (not specifically shown) and following the same bit order as well. The supported bands field  234  indicates the frequency bands supported by the node transmitting this beacon frame and also is encoded as the same as in the PHY header. The max MSDU size field  220  preferably specifies the maximum size, in units of octets, of MSDUs supported by the node transmitting this frame. 
       FIG. 7  illustrates another method embodiment comprising actions  140 - 146 . The method embodiment of  FIG. 7  is a method by which each node can submit a wireless medium access reservation to other nodes. With this method, access reservations can be performed in a distributed manner throughout the network. The method is performable by each node via the access change beacon. 
     Referring to  FIG. 7 , at  140  the method comprises the node determining a need to reserve access to the wireless medium. The access may be for that node to transmit data to one or more other nodes, or for another node to transmit data to one or more other nodes. At  142 , the node generates an access change beacon that contains a reservation request for the wireless medium. The reservation request may be in the form of an altered set of access intervals  180  from that contained in prior beacons or otherwise known to other nodes. At  144 , the node transmits the access change beacon containing the reservation request. At  146 , the node that transmits the access change beacon implements the reservation request (i.e., causes the nodes identified in the altered access interval list to access the medium in accordance with the new access interval list). 
     The nodes that receive the access change beacon must honor the reservation request unless the requested reservation conflicts with current medium access rules regarding which nodes can access the medium at which time periods. If, however, there is no such conflict, the new reservation request is honored by the other nodes after the beacon countdown value  172  has reached zero. This time period permits sufficient time for the reservation request in the access change beacon to propagate throughout the extended neighborhood of the node initiating the change. 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.