Patent Publication Number: US-9848386-B2

Title: Intelligent data network with power management capabilities

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/351,674, filed Jan. 17, 2012, which is a divisional of U.S. patent application Ser. No. 13/083,869, filed Apr. 11, 2011, and now U.S. Pat. No. 8,150,424, which is a continuation of U.S. patent application Ser. No. 12/315,729, filed Dec. 5, 2008, and now U.S. Pat. No. 7,937,121, which is a continuation of U.S. patent application Ser. No. 11/402,182, filed Apr. 11, 2006, and now U.S. Pat. No. 7,466,979, which is a continuation of U.S. patent application Ser. No. 09/779,900, filed Feb. 8, 2001, and now U.S. Pat. No. 7,187,924, which claims the benefit of U.S. Provisional Application Ser. No. 60/180,915, filed Feb. 8, 2000. Each of the foregoing documents is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to the field of electronic communications. 
     2. Discussion of Related Art 
     The current state of the art in networked systems strives to deliver as much of a data payload as fast as possible. Even with the current low power devices and protocols such as IEEE 802.15 and IEEE 1451, the emphasis is on transferring large amounts of data and applications. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a method for implementing wireless two-way communication between at least first and second ambulatory devices comprises first and second steps which are performed while the first and second ambulatory devices are being carried by a person in locomotion on foot. For the first step, during finite time periods following transmission of respective first messages from the first device to the second device, powering on a receiver included in the first device to enable the first device to listen for second messages transmitted from the second device to the first device. For the second step, after each of the finite time periods following the transmission of the respective first messages from the first device to the second device, powering down the receiver included in the first device, and each of the foregoing. 
     According to another aspect of the invention, a method for implementing two-way wireless communication between at least first and second ambulatory devices comprises first and second steps which are performed while the first and second ambulatory devices are being carried by a person in locomotion on foot. For the first step, during finite time periods following reception by the second device of respective first messages from the first device, when the second device needs to communicate with the first device, powering on a transmitter included in the second device and using the transmitter included in the second device to transmit second messages to the first device. For the second step, after each of the finite time periods following reception by the second device of respective first messages from the first device, powering down the transmitter included in the second device and ceasing to use the transmitter included in the second device to transmit second messages to the first device until after the second device receives another first message from the first device. 
     According to another aspect of the invention, a first, ambulatory device capable of engaging in wireless two-way communication with at least a second device comprises a first sensor configured to monitor a physical or physiological condition of a person, a first transmitter, a first receiver, and at least one first controller coupled to the first sensor, the first transmitter, and the first receiver. The at least one first controller is configured to power on the first receiver to listen for second messages from the second device during finite time periods following use of the first transmitter to transmit respective first messages to the second device. The at least one first controller is further configured to cause at least some of the first messages to include data concerning the physical or physiological condition of the person monitored by the first sensor, and to power down the first receiver after each of the finite time periods following use of the transmitter to transmit respective first messages to the second device. 
     According to another aspect of the invention, a second, ambulatory device capable of engaging in two-way communication with at least a first device comprises second circuitry configured to render the second device operable as at least one of a wristwatch, a cellular telephone, a personal data assistant, and a portable music device, a second transmitter, a second receiver, and at least one second controller coupled to the second transmitter and the second receiver. The at least one second controller is configured to power on the second transmitter to transmit second messages to the first device during finite time periods following reception by the second receiver of respective first messages from the first device. The at least one second controller is further configured to power down the second transmitter after transmission of each of the second messages from the second device to the first device. 
     According to another aspect of the invention, a method for implementing two-way communication between at least first and second devices comprises steps of: (a1) during finite time periods following reception by the second device of respective first messages from the first device, using the second device to transmit second messages to the first device; and (a2) after each of the finite time periods following reception by the second device of respective first messages from the first device, ceasing to use the second device to transmit second messages to the first device until after the second device receives another first message from the first device. 
     According to another aspect of the invention, a first device capable of engaging in two-way communication with at least a second device comprises a transmitter; a receiver; and at least one controller. The at least one controller is coupled to the transmitter and the receiver, and is configured to power on the receiver to listen for second messages from the second device during finite time periods following use of the transmitter to transmit respective first messages to the second device. The at least one controller is further configured to power down the receiver after each of the finite time periods following use of the transmitter to transmit respective first messages to the second device. 
     According to another aspect of the invention, a second device capable of engaging in two-way communication with at least a first device comprises a transmitter; a receiver; and at least one controller. The at least one controller is coupled to the transmitter and the receiver, and is configured to power on the transmitter to transmit second messages to the first device during finite time periods following reception by the receiver of respective first messages from the first device. The at least one controller is further configured to power down the transmitter after transmission of each of the second messages from the second device to the first device. 
     According to another aspect of the invention, a first device capable of engaging in two-way communication with at least a second device comprises: means for using the first device to listen for second messages transmitted from the second device to first device during finite time periods following transmission of respective first messages from the first device to the second device; and means for, after each of the finite time periods following the transmission of the respective first messages from the first device to the second device, ceasing to use first device to listen for second messages transmitted from the second device to the first device until after the first device transmits another first message to the second device. 
     According to another aspect of the invention, a second device capable of engaging in two-way communication with at least a first device comprises: means for using the second device to transmit second messages to the first device during finite time periods following reception by the second device of respective first messages from the first device; and means for, after each of the finite time periods following reception by the second device of respective first messages from the first device, ceasing to use the second device to transmit second messages to the first device until after the second device receives another first message from the first device. 
     According to another aspect of the invention, a method for implementing two-way communication between at least first and second devices comprises steps of: (a1) during finite time periods following transmission of respective first messages from the first device to the second device, powering on a receiver included the first device to listen for second messages transmitted from the second device to first device; and (a2) after each of the finite time periods following the transmission of the respective first messages from the first device to the second device, powering off the receiver included in the first device. 
     According to another aspect of the invention, a method for implementing two-way communication between at least first and second devices comprises steps of: (a1) during finite time periods following reception by the second device of respective first messages from the first device, when the second device needs to communicate with the first device, powering on a transmitter included in the second device to transmit second messages to the first device; and (a2) after transmission of each of the second messages from the second device to the first device, powering off the transmitter included in the second device. 
     According to another aspect of the invention, a first device capable of engaging in two-way communication with at least a second device comprises: means for powering on a receiver included the first device to listen for second messages transmitted from the second device to first device during finite time periods following transmission of respective first messages from the first device to the second device; and means for, after each of the finite time periods following the transmission of the respective first messages from the first device to the second device, powering off the receiver included in the first device. 
     According to another aspect of the invention, a second device capable of engaging in two-way communication with at least a first device comprises: means for when the second device needs to communicate with the first device, powering on a transmitter included in the second device to transmit second messages to the first device during finite time periods following reception by the second device of respective first messages from the first device; and means for, after transmission of each of the second messages from the second device to the first device, powering off the transmitter included in the second device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an intelligent network configured in accordance with one illustrative embodiment of the invention; 
         FIG. 2  is a block diagram showing an illustrative embodiment of the MASTER DEVICE and a NODE of the network shown in  FIG. 1 ; 
         FIG. 3  is a flow diagram showing an illustrative example of a software routine that may be executed by a controller of the MASTER DEVICE shown in  FIG. 2 ; and 
         FIG. 4  is a flow diagram showing an illustrative example of a software routine that may be executed by a controller of the NODE shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an illustrative embodiment of an intelligent network  100  that may incorporate various aspects of the present invention. As shown, the intelligent network  100  may include a MASTER DEVICE  102 , a plurality of NODEs  104   a - e , and a peripheral controller  106 . In the embodiment shown, only a single MASTER DEVICE  102  is included in the network  100 . Although such an implementation may provide certain advantages, it should be appreciated that, in alternative embodiments, additional MASTER DEVICES  102  may be employed. It should also be appreciated that additional or no peripheral controllers  106 , and/or additional or fewer NODEs  104  (even a single NODE  104 ) may be employed in alternative embodiments of the invention. Each of the devices in the network  100  may be powered from its own power source (e.g., a battery) so as to permit it to be portable or ambulatory. 
     In the example shown, the MASTER DEVICE  102  communicates with each of the NODEs  104  via a respective wireless communication link  108  (e.g., a radio frequency (RF) link), and also communicates with the peripheral device  106  via a wireless communication link  110  (e.g., an RF link). It should be appreciated, of course, that any of a number of alternative communication media may be used to inter-link these devices, and the invention is not limited to RF links or wireless communication links in general. For example, respective pairs of the devices may alternatively be hardwired, capacitively coupled, or linked by infrared, laser, or audio communications, or the like. 
     Hereinafter, the intelligent network  100  is alternatively referred to as the Personal Local Area Network (“the PLAN”). In the embodiment described herein, the NODEs  104   a - e  of the PLAN  100  are “intelligent,” i.e., they include respective controllers or other circuitry capable of processing data, and the MASTER DEVICE  102  expects to receive only minimal amounts of pre-processed data from the NODEs  104 . Because the data may be processed by each NODE  104  prior to transmission to the MASTER DEVICE  102 , thereby leaving only minimal interpretation at the next application level, the data transmission requirements of the PLAN  100  may be minimal. In order to keep the PLAN  100  intelligent and reliable, a communication link may also be provided from the MASTER DEVICE  102  to the NODEs  104  so that the MASTER DEVICE  102  can occasionally provide data and instructions to the NODEs  104 . According to one aspect of the invention, the MASTER DEVICE  102  is permitted to communicate with the NODEs  104  only during finite periods of time following reception of messages from the respective NODEs  104 . 
       FIG. 2  shows an illustrative embodiment of the MASTER DEVICE  102  and one of the NODEs  104  of  FIG. 1 . As shown, the MASTER DEVICE  102  may include a processor  222  having coupled thereto: a receiver  214 , a transmitter  216 , a user input device  218 , a display  220 , and a memory  224 . Similarly, the NODE  104  may include a processor  202  having coupled thereto: a memory  204 , a display  206 , a user input device  208 , a receiver  210 , and a transmitter  212 . In addition, the NODE  104  may include a sensor  228  coupled to the processor. Examples of sensors  228  that may be included in the respective NODEs  104   a - e  of the PLAN  100  are given below. 
     As illustrated in  FIG. 2 , the transmitter  212  of the NODE  104  may communicate with the receiver  214  of the MASTER DEVICE  102  via a wireless communication link  108   a  (e.g., an RF link), and the transmitter  216  of the MASTER DEVICE  102  may communicate with of course, it is not necessary that a separate transmitter and receiver, the receiver  210  of the NODE  104  via a wireless communication link  108   b  (e.g., an RF link). It should be appreciated, of course, that the transmitter and receiver in each device need not be distinct units, and that a single “transceiver” may alternatively be employed. 
     In one illustrative embodiment, all devices in the network operate on a single, common (RF) frequency. Therefore, in such an embodiment, the transmitters  212  and  216  and the receivers  210  and  214  of  FIG. 2  all would communicate using the same frequency. It should be appreciated, however, that some aspects of the invention may be practiced with transmitter/receiver pairs, or transceivers, operating at different and/or multiple frequencies, and that the invention is not limited to applications wherein only a single frequency is used. In one embodiment, the transmitter  216  and receiver  214  of the MASTER DEVICE  102  are used to communicate with all of the NODEs  104  in the network. It should be appreciated, however, that separate transmitters  216  and receivers  214  may be used to communicate with the respective NODEs  104 , and that the invention is not limited to embodiments wherein only a single transmitter/receiver pair, or transceiver, is employed in any device in the PLAN  100 . 
     In most local area networks (LANs), all processors, sensors and/or actuators of the network must be synchronized. In one embodiment of the invention, the respective devices in the PLAN  100  need not be synchronized. The PLAN  100  may, for example, enable small, variable amounts of data to be transferred asynchronously from the NODEs  104  to the MASTER DEVICE  102 , or vice versa, depending on the transaction being performed. In one illustrative embodiment, operation of the PLAN  100  is based on two assumptions:
         1) The data in the NODEs  104   a - e  may be regenerative and processed at the NODE  104  itself. Each such “intelligent” NODE  104  in the PLAN  100  may have built in intelligence and, as such, may process the data before it is transmitted to the MASTER DEVICE  102 .   2) The MASTER DEVICE  102  may have a look up table for the NODEs  104  that the MASTER DEVICE  102  has permission to listen to. The MASTER DEVICE  102  may parse the header of the incoming messages:
           to determine if there are any messages from its NODEs  104 , and   to see if there are any network control messages.   
               

     In any wireless network, there are two basic devices used for inter-device communication: (1) a transmitter (e.g., one of the transmitters  212  and  216  of  FIG. 2 ), and (2) a receiver (e.g., a corresponding one of the receivers  210  and  214  of  FIG. 2 ). When either of these devices is operational, it consumes power. Thus, in order to conserve power, is desirable to power down each transmitter and receiver in the network as often as possible. 
     Most networks have an internal timing mechanism for keeping track of time, and every node in the network is given the same timing information, or works from the same time base. Typically, devices in a network are allocated certain time windows during which they are permitted to transmit and certain time windows when they must listen for incoming messages, and each device transmits and receives only during these specified times. Because each device is required to turn on its receiver during each scheduled “receive” time window, i.e., each time it might receive a message from the network, the receiver consumes power unnecessarily each time no messages are received during such windows. 
     Additionally, to keep the clocks of all devices in a network synchronized (thereby assuring that each device transmits/receives messages during the appropriate time windows), prior art networks typically communicate synchronization information among devices in the network (at least occasionally) using intra-network messages or signals. Because the device transmitters/receivers and associated time keeping circuitry must be operational to communicate and process this information, a significant amount of power is consumed merely in keeping the network synchronized. 
     In contrast to such networks, the PLAN  100  may operate asynchronously, i.e., without specified transmit/receive time windows for the network devices. For example, in one illustrative embodiment, the NODE(s)  104  initiate all data transfers to the MASTER DEVICE  102  according to some specified criteria (which may be random) or whenever they determine such transfers should take place, and each NODE  104  expects to receive data only for a prescribed period of time after that NODE  104  has made a transmission to the MASTER DEVICE  102 . Thus, in this embodiment, the MASTER DEVICE  102  is permitted to communicate with each NODE  104  only during this prescribed time period after the MASTER DEVICE  102  has received a message from that NODE  104 . (This is akin to a pay telephone from which an employee can call his or her boss, but only when the employee calls the boss can the boss tell the employee what to do. This analogy assumes the boss can never initiate a phone call to the pay phone). 
     Therefore, in the above-described embodiment, power consumed by the NODEs  104  may be minimized by powering on the receivers of the NODEs  104  (e.g., the receiver  210 ) only for brief periods of time after the NODEs  104  have transmitted respective messages to the MASTER DEVICE  102 , and not powering them on repeatedly during their specified “receive” time windows, as is done in prior art networks. In addition, power need not be consumed by the transmitters, receivers and associated circuitry of the network devices of the PLAN  100  to ensure that they all are synchronized with one another. It should be appreciated that, in addition to the transmitters and receivers, other devices and/or portions of other devices in the MASTER DEVICE  102  and/or NODEs  104  may also be powered down during intervals when their use is not required, thereby further conserving power in the system. 
     Because, in the embodiment described above, each NODE  104  knows that it will not receive a message from the MASTER DEVICE  102  unless it first transmits a message to the MASTER DEVICE  102 , all NODEs  104  can power down both their transmitters  212  and their receivers  210  until they are ready to transmit messages to the MASTER DEVICE  102 . When a NODE  104  desires to initiate communication with the MASTER DEVICE  102 , only then does that NODE  104  need to turn on its transmitter  212 . And, only after that NODE  104  has completed the transfer of the message to the MASTER DEVICE  102  does the NODE  104  need to turn on its receiver  210  to receive a reply message, if any, from the MASTER DEVICE  102 . 
     Similarly, in the embodiment described above, only when the MASTER DEVICE  102 : (1) has just recently received a message from the NODE  104 , and (2) has a message to communicate to the NODE  104 , is the MASTER DEVICE  102  required to turn on its transmitter  216 . 
     In one implementation, each message transmitted from the NODE  104  to the MASTER DEVICE  102  may include information identifying a time window during which the NODE  104  expects to send a subsequent message to the MASTER DEVICE  102 . In such an embodiment, the MASTER DEVICE  102  can also power down its receiver  214 , after receiving this information, until the beginning of the identified time window. The time window for the subsequent transmission may, for example, be selected at random (e.g., using a random number generator or the like) so as to minimize the risk of collisions with other messages transmitted on the PLAN  100 . In one embodiment, if no such time window is identified or no message is received during a specified time window, the MASTER DEVICE  102  may then automatically turn on its receiver  214  and continually listen for incoming messages. After not receiving any incoming messages for a particular time period, the MASTER DEVICE  102  may even shut down its receiver indefinitely (e.g., until subsequent user intervention such as with user input device  218 ). 
     In another implementation, in response to receiving each messages from a respective NODE  104 , the MASTER DEVICE  102  may send a reply message to the NODE  104  indicating when the MASTER DEVICE  102  expects to next receive a subsequent message from the NODE  104 . The MASTER DEVICE  102  therefore may schedule the times of subsequent message transmissions from the various NODEs  104  and may power down its receiver  214  at all other times, thereby conserving power. The scheduled time windows for the subsequent message transmissions by the respective NODEs  104  may, for example, be selected at random (e.g., using a random number generator or the like) so as to minimize the risk of collisions with other messages transmitted on the PLAN  100 , or may be deliberately scheduled so as to avoid any such collisions all together. As with the embodiment described above, if no such time window is identified, or no message is received during a specified time window, the MASTER DEVICE  102  may then automatically turn on its receiver  214  and continually listen for incoming messages. After not receiving any incoming messages for a particular time period, the MASTER DEVICE  102  may even shut down its receiver indefinitely (e.g., until subsequent user intervention such as with user input device  218 ). 
     In yet another implementation, the receiver  214  of the MASTER DEVICE  102  may simply remain on at all times the MASTER DEVICE  102  is in use. Such an implementation may make sense in an embodiment of the PLAN  100  including a large number of NODEs  104  that frequently transmit information to the MASTER DEVICE  102 , or in an embodiment wherein power management of the MASTER DEVICE  102  is not a significant concern. 
     Example implementations of routines that may be performed by the MASTER DEVICE  102  and any one of the NODEs  104  in accordance with an embodiment of the invention are shown in  FIGS. 3 and 4 , respectively. The routine  300  of  FIG. 3  may, for example, be executed by the processor  222  of  FIG. 2  in response to instructions stored in the memory  224 . The routine  400  of  FIG. 4  may, for example, be executed by the processor  202  of  FIG. 2  in response to instructions stored in the memory  204 . 
     With regard to the illustrative routines  300  and  400 , it should be appreciated that the precise order of the method steps is not critical, and that the invention is not limited to embodiments that perform method steps in precisely in the order shown. Additionally, it should be appreciated that the method steps shown in  FIGS. 3 and 4  represent only two of numerous possible routines that can achieve the desired results, and the invention is not limited to the particular routines shown. Further, it should be understood that some embodiments of the invention can perform fewer than all of the functions performed by the method steps illustrated in  FIGS. 3 and 4 , and that the invention is not limited to embodiments which employ all of the functions performed by the illustrated routines. 
     Referring to  FIG. 3 , the routine  300  begins at a step  302 , wherein it is determined whether “scheduled reception” is enabled for the MASTER DEVICE  102 . Scheduled reception may refer, for example, to a situation wherein a NODE  104  indicated (in a message previously sent to the MASTER DEVICE  102 ) a time window in which it expected to send a subsequent message, or to a situation in which the MASTER DEVICE  102 , in a reply message to a NODE  104 , indicated to the NODE  104  when the MASTER DEVICE  102  expected to receive a subsequent message from the NODE  104 . In one implementation, when schedule reception is not enabled, the receiver  214  is powered on at all times the MASTER DEVICE  104  is in operation. When schedule reception is enabled in such an implementation, the receiver  214  of the MASTER DEVICE  102  may be powered on only during time intervals scheduled by the MASTER DEVICE  102  or one or more of the NODEs  104  as discussed above, or upon the failure of the MASTER DEVICE  102  to receive any incoming messages for a particular period of time, as also discussed above. 
     When, at the step  302 , it is determined that scheduled reception is enabled, the routine  300  proceeds to a step  318 , wherein it is determined whether it is currently a time window during which the MASTER DEVICE  102  should be looking for incoming messages from NODEs  104 . 
     When, at the step  318 , it is determined that it is not currently a receive interval, the routine  300  proceeds to a step  320 , wherein the receiver  214  is powered down. After the step  320 , the routine  300  returns to the step  302 . 
     When, at the step  318 , it is determined that it is currently a receive interval, the routine  300  proceeds to a step  304 , wherein the receiver  214  of the MASTER DEVICE  102  is powered up. 
     When, at the step  302 , it is determined that scheduled reception is not enabled, the routine  300  proceeds immediately to the step  304 , without first proceeding to the step  318  to determine whether it is currently a receive interval. 
     After powering up the receiver at the step  304 , the routine  300  proceeds to a step  306 , wherein it is determined whether a message has been received from a NODE  104 . 
     When, at the step  306 , it is determined that no message has been received from a NODE  104 , the routine  300  returns to the step  302 . 
     When, at the step  306 , it is determined that a message has been received from a NODE  104 , the routine  300  proceeds to a step  308 , wherein the receiver  214  is powered down. 
     After the step  308 , the routine  300  proceeds to a step  310 , wherein it is determined whether a reply has been requested by the NODE  104  that sent the received message. 
     When, at the step  310 , it is determined that a reply has been requested by the transmitting NODE  104 , the routine  300  proceeds to steps  322  and  324 , wherein the transmitter  216  of the MASTER DEVICE  102  is powered up and used to transmit a reply message, as well as any other messages awaiting transmission, to the transmitting NODE  104 . 
     After the step  324 , the routine  300  proceeds to a step  314 , wherein the transmitter  216  of the MASTER DEVICE  102  is powered down. 
     When, at the step  310 , it is determined that no reply has been requested by the transmitting NODE  104 , the routine  300  proceeds to a step  312 , wherein it is determined whether any messages (other than a requested reply) are awaiting to be transmitted from the MASTER DEVICE  102  to the transmitting NODE  104 . It should be appreciated that such messages awaiting transmission to the NODE  104  may also be embedded in a requested reply message to the transmitting NODE  104  (identified at the step  310 ). 
     When, at the step  312 , it is determined that a message is waiting for transmission to the transmitting NODE  104 , the routine  300  proceeds to the steps  322  and  324 , wherein the transmitter  216  of the MASTER DEVICE  102  is powered up and the message awaiting transmission is transmitted to the NODE  102  that sent the original message to the MASTER DEVICE  102 . 
     When, at the step  312 , it is determined that no messages are awaiting transmission to the transmitting NODE  104 , the routine  300  proceeds to the step  314 , wherein the transmitter  216  of the MASTER DEVICE  102  is powered down. 
     After the step  314 , the routine  300  returns to the step  302 , wherein it is again determined whether scheduled reception is enabled for the MASTER DEVICE  102 . If the MASTER DEVICE  102  requested a reply from the NODE  104  to which it sent a message at the step  324 , a receive interval may begin immediately so that the MASTER DEVICE  102  can receive such a reply message when it is subsequently sent by the NODE  104 . 
     Referring now to  FIG. 4 , the illustrative routine  400 , which may be implemented by each of the NODEs  104 , begins at a step  402 , wherein it is determined whether the NODE  104  executing the routine  400  has accumulated and processed data which is ready for transmission to the MASTER DEVICE  102 . 
     When, at the step  402 , it is determined that the NODE  104  does have processed data ready for transmission to the MASTER DEVICE  102 , the routine  400  proceeds to steps  404 - 408 , wherein the transmitter of the NODE  104  (e.g., the transmitter  212  of  FIG. 2 ) is powered up (step  404 ), is used to transmit the processed data to the MASTER DEVICE  102  (step  406 ), and is then powered down ( 408 ). 
     After the step  408 , the routine  400  proceeds to a step  410 , wherein the receiver of the NODE  104  (e.g., the receiver  210  of  FIG. 2 ) is powered up. 
     After the step  410 , the routine  400  proceeds to a step  412 , wherein it is determined whether a reply message has been received from the MASTER DEVICE  102  in response to the message transmitted at the step  406 . 
     When, at the step  412 , it is determined that a reply message has been received from the MASTER DEVICE  102 , the routine  400  proceeds to a step  418 , wherein the receiver of the NODE  104  is powered down. 
     After the step  418 , the routine  400  proceeds to a step  420 , wherein it is determined whether a reply was requested by the MASTER DEVICE  102  in response to the message received from the MASTER DEVICE  102  at the step  412 , for example, to acknowledge receipt of the message. 
     When, at the step  420 , it is determined that a reply was requested by the MASTER DEVICE  102 , the routine  400  proceeds to the steps  404 - 408 , wherein the reply is transmitted to the MASTER DEVICE  102 . 
     When, at the step  420 , it is determined that no reply was requested by the MASTER DEVICE  102 , the routine  400  returns to the step  402 . 
     When, at the step  412 , it is determined that no reply has yet been received from the MASTER DEVICE  102 , the routine  400  proceeds to a step  414 , wherein it is determined whether the interval during which the MASTER DEVICE  102  is permitted to communicate with the NODE  104  has elapsed. If the reply interval for the MASTER DEVICE  102  has not yet elapsed, the routine  400  returns to the step  412 . 
     When, at the step  414 , it is determined that the reply interval for the MASTER DEVICE  102  has elapsed, the routine  400  proceeds to a step  416 , wherein the receiver of the NODE  104  (e.g., the receiver  210 ) is powered down. 
     After the step  416 , the routine  400  returns to the step  402 , wherein it is again determined whether the NODE  104  has processed data ready for transmission to the MASTER DEVICE  102 . 
     It should thus be appreciated that, in the described embodiment of  FIGS. 3 and 4 , the NODEs  104  may initiate all data transfers between themselves and the MASTER DEVICE  102 , but that, after such a transfer has been initiated, communication between the two devices may continue indefinitely until one decides not to request a reply from the other. 
     In one example embodiment, there are two major types of messages that may be communicated over the PLAN  100 , each with subclasses of messages underneath. For example, “class one” messages may be unsolicited messages, and “class two” messages may be solicited messages. Both the NODEs  104  and the MASTER DEVICE  102  may transmit either class of messages. 
     Class one messages may, for example, be messages that require no response from the NODE  104  or the MASTER DEVICE  102 . With class one messages, it may be assumed that the data was transmitted properly. This embodiment of the PLAN  100  may take advantage of the intelligence of its sensors by ensuring that, if there is a missing transmission and a class one message is not transmitted, the operation of the system employing the network is not compromised. 
     Class two messages may, for example, be messages that require a response or acknowledgement. The transmitting device (e.g., a NODE  104  or the MASTER DEVICE  102 ) may transmit a flag in the data packet of each class two message which requests that the receiving device respond to the message subclass. 
     The class of each message (i.e., class one or class two) may, for example, affect the outcome of the steps  310  and  420  of the illustrative routines of  FIGS. 3 and 4 , respectively. That is, referring to  FIG. 3 , if it is determined (at the step  310 ) that the message received from the NODE  104  is a class two message, the routine  300  may proceed to the step  322 , wherein the transmitter  216  is powered up and an acknowledge or reply message is immediately sent to the NODE  104 . If, on the other hand, it is determined (at the step  310 ) that the message received from the NODE  104  is a class one message, the routine  300  may instead proceed to the step  312 , wherein a message is transmitted to the NODE  104  only if the MASTER DEVICE  102  happens to have an outgoing message ready to send. 
     Similarly, referring to  FIG. 4 , if it is determined (at the step  420 ) that the message received from the MASTER DEVICE  102  (at the step  412 ) is a class two message, the routine  400  may proceed to the step  404 , wherein the transmitter  212  is powered up and an acknowledge or reply message is sent to the MASTER DEVICE  102 . If, on the other hand, it is determined (at the step  420 ) that the message received from the MASTER DEVICE  102  is a class one message, the routine  400  may instead proceed to the step  402 , wherein it waits until the NODE  104  is again ready to transmit processed data to the MASTER DEVICE  102 . 
     Thus, the above-described embodiment of the PLAN  100  can provide a reliable link whenever one or more class two messages are sent. Each NODE  104  may control the data throughput rate of the transfer. The MASTER DEVICE  102  may service other NODEs  104  during a reliable link transfer. Class two messages may, for example, be initiated from the peripheral controller  106  (described below) to the MASTER DEVICE  102 , from a NODE  104  (that requires reliable data transfer), or from the MASTER DEVICE  102  (e.g., trying to negotiate network congestion). 
     One advantageous feature of at least some embodiments of this network is the ability of each NODE  104  to provide processed information to the MASTER DEVICE  102 . The MASTER DEVICE  102  may, for example, simply store the processed data, further process the data, display a representation of the data, e.g., on the display  220 , and/or pass the data onto the peripheral controller  106  (or multiple peripheral controllers  106 ). The peripheral controller  106 , if employed, may be any of a number of devices, and the invention is not limited to any particular type of controller. The peripheral controller  106  may, for example, be an “intelligent” device such as application-based microcontroller or computer. The applications of the peripheral controller may, for example, include:
     Watch display   Physiological Monitor   an RF Router   a PC Interface   a two-way pager controller   a Cellular phone controller   a land phone controller   

     Furthermore, the functionality of either the MASTER DEVICE  102  and/or the peripheral controller  106  may be distributed across one another or across additional controllers for efficiency, space or energy savings, or any other reason. 
     The sensor  228  in each NODE  104  may take on any of numerous forms, and the invention is not limited to any particular type of sensor. In some embodiments, one or more NODEs  104  may use a microcontroller to process an analog signal from the sensor  228  to reduce the analog signal to a simple digital data stream for transmission to the MASTER DEVICE  104  in the PLAN  100 . 
     An example of a sensor  228  that may be employed is a heart rate monitor. Such a NODE  104  may, for example, process a heart beat wave form to determine how many heart beats there are per minute, and report the calculated number of heartbeats, and perhaps the standard deviation thereof as well, to the MASTER DEVICE  102 . The MASTER DEVICE  102  may then receive the data packet, check the authenticity of the sender, and store the data packet in an appropriate memory location. The MASTER DEVICE  102  and/or peripheral controller  106  may then, for example, retrieve and display the heart rate data on a watch-like device (e.g., a digital wristwatch) on a person&#39;s wrist. As used herein, the term “wristwatch” is not limited to devices capable of keeping time. Rather, the term “wristwatch” is intended to refer to any device that may be secured to the wrist of a person that is capable of displaying information, whether or not the devices also keep time. The implementation discussed above may be contrasted to conventional heart rate monitors which provide only a beat transmission and require the receiving device to do the computation necessary to obtain the heart rate information. 
     Each NODE  104  may alternatively employ any of numerous other types of sensors  228 . Another example of a sensor  228  that may be employed in one or more of the NODEs  104  is an accelerometer. The output of such an accelerometer may, for example, be analyzed by the processor  202  to measure the foot contact times of a person, and the foot contact times may then be used to calculate the person&#39;s pace, speed, distance traveled, etc. An example of such a NODE  104 , and the employment of such a NODE  104  in a PLAN  100  which also includes a wristwatch-tune MASTER DEVICE  102  and a heart rate monitor (another NODE  104 ) is disclosed in co-pending patent application Ser. No. 09/643,165, filed on Aug. 21, 2000, and entitled MONITORING ACTIVITY OF A USER IN LOCOMOTION ON FOOT, the entire contents of which is hereby incorporated herein by reference. 
     Thus, a NODE  104  employing an accelerometer as its sensor  228  may, for example, transmit the foot contact time of the person, the distance traveled by the person, the current pace of the person, and/or the average pace of the person, as one or more values to the MASTER DEVICE  102  (e.g., a wristwatch), for processing, display, and/or transmission to the peripheral controller  106 . The MASTER DEVICE  102  may, in turn, send calibration data or the like back to the NODE  104  during the predetermined, finite time periods after the MASTER DEVICE  102  receives such information from the NODE  104 . 
     The PLAN  100  according to the invention may support any number of NODEs  104 . There may, however, be a limit as to how many NODEs  104  can operate at one time. The PLAN  100  may, for example, be configured to transmit only short distances. Thus, the number of NODEs  104  in the PLAN  100  at any one time may be limited by physical constraints. The PLAN  100  may be such that, once the MASTER DEVICE  102  has a valid routing table of acceptable NODEs  104 , whenever any of the routing table NODEs  104  are available, the data can be collected and moved into storage. As the NODEs  104  go out of range, the MASTER DEVICE  102  may, for example, simply stop recording the data. 
     Embodiments of the PLAN  100  may take on any of a number of forms. In one example, the MASTER DEVICE  102  may be embodied as a wrist watch, which has buttons (e.g., the user input device  218 ) and a display (e.g., the display  220 ), and the NODE(s)  104  may be embodied as a device including one or more intelligent physiological sensors  228  configured to monitor conditions such as: heart rate, EKG, foot contact time or foot loft time during footsteps, Pulse oximetry, blood pressure, EMG, blood glucose, body temperature, etc. Alternatively, the NODEs  104  may, for example, be integrated into bathroom scales, automotive computers, or automatic door openers for automotive and security systems. Conceivably, any intelligent device can be brought into this network as a NODE  104  or MASTER DEVICE  102 . The PLAN  100  may, for example, be integrated into a system employing two-way pager devices so that physiological data can be sent onto the Internet directly from a person&#39;s body. The PLAN  100  may also be integrated into a system employing a digital wireless phone so that the data can be sent into the phone network. The PLAN  100  may further be integrated into a system employing a portable music machine, or a personal digital assistant, or any other “intelligent” device. 
     A NODE  104  of the PLAN  100  may, for example, be integrated into a small device that acts as a gateway device between other networks, such as IEEE 802.15, IEEE 1451, the HOME RF, Bluetooth, 10× or other such networks. By doing this, as one moves through a space, the NODE  104  of the PLAN  100  may become available to other networks, and the data from these other networks may become available to the PLAN  100 , and the peripheral controller(s)  106  in the PLAN  100 . In addition, by providing sufficient intelligence in the MASTER DEVICE  102  and an output port therefrom, the MASTER DEVICE  102  may also act like a gateway between different network protocols (e.g., PLAN  100  to Serial, RF to IEEE 802.15, RF to RF, etc.). 
     In one embodiment, the packet size of each message transmitted using the PLAN  100  may be 1/X of the total bandwidth of the system, where X is determined to be the acceptable guaranteed bandwidth of the system. In such an embodiment, data may be broken up into multiple (Y) packets, and with no one NODE  104  being permitted to consume more than X·Y percent of the available bandwidth at any one time. All NODEs  104  may have as much intelligence as required to meet or exceed the maximum network bandwidth. 
     Having described several embodiments of the invention in detail, various modifications and improvements will readily occur to those skilled in the art. Such modifications and improvements are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only, and is not intended as limiting. The invention is limited only as defined by the following claims and the equivalents thereto.