Abstract:
A peripheral device can reduce its reconnection time to a mobile communication terminal in a short-range personal wireless communication system including the peripheral device and the mobile communication terminal that performs short-range wireless communication. A short-range communication method of a node in a short-range personal wireless communication system in which communication is performed between at least one Personal Area Network (PAN) and multiple nodes is provided. A peripheral PAN is monitored to perform short-range communication, and at least one PAN is selected as a result of the monitoring; generating channel information for the selected PAN. The generated channel information is transmitted to a peripheral device connected to the node, and the selected PAN is connected with.

Description:
PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Jul. 31, 2007 and assigned Serial No. 2007-77202, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a channel switching method, and more particularly, to a method for switching channels through which content data is received in a ZigBee network system, and a ZigBee network system thereof. 
         [0004]    2. Description of the Related Art 
         [0005]    A Wireless Personal Area Network (WPAN) is a legacy Personal Area Network (PAN) realized in a wireless manner. In a PAN, unlike in the well-known Local Area Network (LAN) or Wireless Local Area Network (WLAN), each person has his/her own unique network. For example, each device possessed by one person forms one network for the person&#39;s convenience. 
         [0006]    A mobile communication terminal can connect with a headset using ZigBee communication, which is a kind of PAN, and can control the connected headset to transmit and reproduce multimedia data. 
         [0007]    When a PAN is broadcasting multimedia data in a public mode, the headset can receive the multimedia data broadcasted from the PAN without a separate authentication procedure. However, the headset cannot receive multimedia data without undergoing the authentication procedure when the PAN is in a private mode. While the mobile communication terminal can simply process the complex authentication procedure with the PAN, the headset has difficulty carrying out the calculation necessary for the authentication procedure since it has a simple structure compared with the mobile communication terminal. Thus, the headset should be connected to the mobile communication terminal in the private mode where the authentication procedure is essential. When the mobile communication terminal completes the authentication procedure with the PAN, the headset receives and reproduces the data broadcasted from the PAN through the mobile communication terminal. 
         [0008]    However, if the mobile communication terminal closes the connection with the old PAN to access (or join with) another PAN, the connection between the headset and the PAN is also disconnected. This is particularly true in the private mode. Since the headset&#39;s authentication with the PAN has already been completed through the mobile communication terminal, if the connection between the mobile communication terminal and the PAN is closed, the connection is closed as the headset cannot process the authentication procedure with the PAN. In addition, if the headset is not connected to the mobile communication terminal, it cannot perform its call function, causing inconvenience to the user. 
         [0009]    Therefore, it is preferable for the headset to be reconnected to the mobile communication terminal that has moved to another PAN. To this end, the headset accesses all channels registered in the ZigBee network. The headset transmits a Join Request (or Connect Request) to all terminals connected to each PAN that it has accessed, and if a specific mobile communication terminal grants (confirms) the Join Request, the headset determines that the mobile communication terminal has accessed the corresponding PAN. 
         [0010]    For example, if it is assumed that the frequency band where the ZigBee network is formed is 2.4 GHz and a total of 16 channels CH.11˜CH.26 are formed, the headset whose connection to the mobile communication terminal is closed cannot determine to which channel or PAN the mobile communication terminal has accessed. The headset accesses the channels in turn starting from the first channel, and transmits a Join Request to all terminals in the accessed channel to thereby check whether the mobile communication terminal has joined in the corresponding channel. Even for the same channel, multiple PANs having different PAN Identifications (IDs) may exist in the channel, so the headset should access all channels and PANs to check whether the mobile communication terminal has accessed the corresponding channels and PANs. 
         [0011]    In this way, the headset should access all channels and PANs of the ZigBee network to check the mobile communication terminal&#39;s access/non-access thereto every time the mobile communication terminal switches its PAN, increasing the time required in a reconnection process. The increase in the reconnection time causes an increase in the time for which the headset cannot receive multimedia data from the mobile communication terminal. Accordingly, the user may not reproduce the multimedia data in the reconnection process for a long time, causing much inconvenience. 
         [0012]    Therefore, there is a demand for a mobile communication terminal that does not need a long time for reconnection between the headset and the mobile communication terminal, and can conveniently reproduce the multimedia data. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention provides a channel switching method for switching channels through which content data is received in a ZigBee network system capable of reducing the time for which the headset is reconnected to the mobile communication terminal, and a ZigBee network system thereof. 
         [0014]    According to one aspect of the present invention, there is provided a short-range communication method of a node in a short-range personal wireless communication system in which communication is performed between at least one Personal Area Network (PAN) and multiple nodes. A peripheral PAN is monitored to perform short-range communication, and at least one PAN is selected as a result of the monitoring. Channel information for the selected PAN is generated. The generated channel information is transmitted to a peripheral device connected to the node, and the selected PAN is connected with. 
         [0015]    According to another aspect of the present invention, there is provided a short-range communication apparatus of a node in a short-range personal wireless communication system in which communication is performed between at least one Personal Area Network (PAN) and multiple nodes. The apparatus includes a controller for monitoring a peripheral PAN to perform short-range communication, and controlling a communication module to connect with a PAN selected as a result of the monitoring. The apparatus also includes a display for displaying the monitoring result; a key input unit for receiving a user input for selecting at least one PAN from the monitoring result. The apparatus further includes a channel information generator for generating channel information for the selected PAN, and the communication module for transmitting the generated channel information to a peripheral device connected to the node, and connecting with the selected PAN. 
         [0016]    According to a further aspect of the present invention, a mobile communication terminal is provided for exchanging data with a coordinator that has formed a first Personal Area Network (PAN) in a ZigBee network system that perform ZigBee communication. The mobile communication terminal includes a channel information generator for generating channel information for a second PAN when the terminal intends to switch the current PAN to the second PAN other than the first PAN, formed by another coordinator. The mobile communication terminal also includes a ZigBee communication module for transmitting the generated channel information to a connected peripheral device. 
         [0017]    According to yet another aspect of the present invention, there is provided a short-range personal wireless communication system in which communication is performed between at least one Personal Area Network (PAN) and multiple nodes. The short-range personal wireless communication includes the node for monitoring a peripheral PAN to perform short-range communication, selecting at least one PAN as a result of the monitoring, generating channel information for the selected PAN, and transmitting the generated channel information. The short-range personal wireless communication also includes a peripheral device for receiving the channel information from the node, and when the connection with the node is released, connecting with the selected PAN using the channel information and resuming the connection with the node. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
           [0019]      FIG. 1  is a diagram illustrating a ZigBee network system according to an embodiment of the present invention; 
           [0020]      FIG. 2  is a block diagram illustrating a schematic structure of a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention; 
           [0021]      FIG. 3  is a signaling diagram illustrating a channel switching method in a ZigBee network system according to an embodiment of the present invention; 
           [0022]      FIG. 4  is a flowchart illustrating a channel switching method of a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention; 
           [0023]      FIG. 5  is a flowchart illustrating a channel switching method of a headset in a ZigBee network system according to an embodiment of the present invention; 
           [0024]      FIG. 6  is a flowchart illustrating a method for resuming a connection between a headset and a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention; and 
           [0025]      FIG. 7  is a diagram illustrating the PAN search result in a ZigBee network according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    Preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. Similar components are designated by similar reference numerals although they are illustrated in different drawings. Detailed descriptions of constructions or processes known in the art may be omitted to avoid obscuring the subject matter of the present invention. 
         [0027]    Herein, a PAN that a mobile communication terminal was accessing (joining in) before it switches the PAN will be referred to as a ‘first PAN’, while a PAN that the mobile communication terminal has newly accessed after closing the connection with the first PAN will be referred to as a ‘second PAN’. In addition, a communication network including at least one PAN, which is an upper concept of PAN, is called ‘switched channel’. Particularly, when the mobile communication terminal switches its accessed PAN from the first PAN to the second PAN, the channel switched due to the switching of the PAN will be referred to herein as a ‘switched channel’. As a specific example, if the first PAN is included in CH. 12  and the second PAN is included in CH.  14 , the switched channel is CH.  14 . 
         [0028]      FIG. 1  is a diagram illustrating a ZigBee network system according to an embodiment of the present invention. 
         [0029]    A first PAN and a second PAN, and mobile communication terminals  10  and  14  connected to each PAN are shown in the drawing. Among the mobile communication terminals, a mobile communication terminal including a ZigBee communication module serving as a ZigBee coordinator  12  will be referred to as a ‘coordinator terminal 10’, and a mobile communication terminal including a ZigBee communication module serving as a ZigBee node  16  will be referred to as a ‘node terminal 14’. The coordinator terminal  10  forms a Personal Area Network, i.e., PAN, that broadcasts content data, or forms a channel including at least one PAN, and broadcasts content data to the node terminal  14  that has entered the corresponding PAN or channel. The content data broadcasted from the coordinator terminal  10  is multimedia data that can undergo streaming, such as, for example, MPEG Audio Layer-3 (MP3), Moving Picture Experts Group (MPEG), etc. 
         [0030]    The node terminal  14  that receives the content data broadcasted in the corresponding PAN is connected to the first PAN or second PAN formed by the coordinator terminals  10 . The node terminals  14  each select and access any one of the PANs or channels formed by its associated coordinator terminal  10  in the ZigBee network, and receive the content data broadcasted from the coordinator terminal  10 . The node terminals  14  each transmit the received content data to its associated headset  18 , and the headset  18  reproduces the content data received through the node terminal  14 . 
         [0031]    According to another embodiment of the present invention, since the headset  18  includes a ZigBee communication module separate from that of the mobile communication terminal, it can perform ZigBee communication with the coordinator terminal  10 . Since the headset  18  is capable of ZigBee communication, it can directly receive content data from the coordinator terminal  10  without passing through the node terminal  14 , and reproduce the received content data. 
         [0032]    The ZigBee communication module may previously have information on the PAN or channel that can be formed in the ZigBee network, or can be provided with information on the formed PAN or channel from the ZigBee network. Therefore, the headset  18  capable of ZigBee communication, like the node terminal  14 , can directly access the PAN or channel and receive content data there from. 
         [0033]    In particular, when the PAN is in the public mode, since the headset  18  has no need for the authentication procedure, it can receive the content data broadcasted from the coordinator terminal  10  by simply accessing the PAN, unlike in the private mode. In addition, the headset  18  can directly convert the content data received from the PAN or channel by encoding/decoding the content data, and reproduce the converted content data. 
         [0034]    Although the device connected to the node terminal  14  is limited herein to the headset  18 , by way of example, the device connected to the node terminal  14  should not necessarily be limited to the headset. All devices capable of ZigBee communication, including a ZigBee communication module therein, such as printer and Personal Digital Assistance (PDA) as well as the headset, can be connected to the node terminal  14  to receive content data therefrom. 
         [0035]      FIG. 2  is a block diagram illustrating a schematic structure of a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention. 
         [0036]    A mobile communication terminal  14  according to an embodiment of the present invention includes a Radio Frequency (RF) unit  22 , a key input unit  24 , a display  26 , a memory  28 , a ZigBee communication module  30 , a multimedia reproducer  32 , a channel information generator  38 , and a controller  34 . The mobile communication terminal  14 , connected to a headset  18  including a ZigBee communication module  36 , performs short-range communication. 
         [0037]    The RF unit  22  performs a wireless communication function of the mobile communication terminal  14 . The RF unit  22  includes an RF transmitter (not shown) for frequency-up-converting and amplifying a transmission signal, and an RF receiver (not shown) for low-noise-amplifying and frequency-down-converting a received signal. 
         [0038]    The key input unit  24  includes keys by which the terminal  14  can receive numerical and character inputs, and keys used for setting various functions. The key input unit  24  receives inputs from the user. If the controller  34  searches PANs in the ZigBee network, the key input unit  24 , according to an embodiment of the present invention, can receive a user input for selecting any one of the searched PANs. 
         [0039]    The display  26 , which can be made up of a Liquid Crystal Display (LCD), outputs various display data generated by the mobile communication terminal  14 . When the LCD is realized in a touch screen manner, the display  26  can serve even as an input means. 
         [0040]    According to an embodiment of the present invention, the display  26  can display the PAN search result in the ZigBee network, under the control of the controller  34 . In addition, the display  26  can display information on the content data reproduced in the headset  18 . For example, if the content data is a music file, the display  26  displays the title, singer, album name, etc. 
         [0041]    The memory  28  can be composed of a program memory and a data memory. The memory  28  stores therein a variety of information necessary for controlling an operation of the mobile communication terminal  14 . The memory  28  according to an embodiment of the present invention, under the control of the controller  34 , can store content data reproduced by the headset  18 , and can also store channel information for each PAN formed in the ZigBee network. 
         [0042]    The channel information includes a channel number of a switched channel in which a second PAN selected by the mobile communication terminal  14  among the PANs searched by the mobile communication terminal  14  is included, and a PAN ID of the second PAN. Further, the channel information can include configuration information containing a beacon period of the second PAN, used for allowing the headset  18  to readily access the second PAN. 
         [0043]    The coordinator terminal  10  can form a different communication network according to the PAN ID. For example, a communication network with a channel number “13” and a PAN ID “ID — 113” and a communication network with a channel number “13” and a PAN ID “ID — 256” are different communication networks though they exist in the same channel. That is, the coordinator terminal  10  having its own unique PAN ID can form a communication network “PAN” corresponding to a lower concept of the channel in the same channel. Therefore, switching of the PAN connected to the mobile communication terminal  14  means switching of a channel number and a PAN ID. The channel information includes both the channel number and the PAN ID to correctly notify the headset  18  of the second PAN that the mobile communication terminal  14  has accessed. 
         [0044]    The ZigBee communication module  30  is a communication module for performing ZigBee communication. According to an embodiment of the present invention, since the mobile communication terminal  14  includes the ZigBee communication module  30 , it can serve as the ZigBee coordinator  12  or the ZigBee node  16  in the ZigBee network. 
         [0045]    Referring back to  FIG. 1 , the mobile communication terminal  10  serving as the ZigBee coordinator  12  forms a PAN, which is a LAN, and broadcasts content data to the formed PAN. The mobile communication terminal  14  serving as the ZigBee node  16  accesses the PAN or channel formed by the ZigBee coordinator  12 , and receives content data broadcasted from the ZigBee coordinator  12 . 
         [0046]    The multimedia reproducer  32  reproduces multimedia data in the content data broadcasted from the coordinator terminal  10  or previously stored in the memory  28 . 
         [0047]    According to an embodiment of the present invention, the multimedia reproducer  32  can encode/decode the multimedia data received from the coordinator terminal  10 . The multimedia data encoded/decoded by the multimedia reproducer  32  can be transmitted to the headset  18  by means of the ZigBee communication module  30  and then reproduced. 
         [0048]    The channel information generator  38  generates channel information under the control of the controller  34 . When a user input for selecting one of the searched PANs is selected by means of the key input unit  24 , the channel information generator  38  generates channel information for the selected PAN. Also, the channel information generator  38  can generate terminal information. Before the node terminal  14  moves from the current PAN to a new PAN, the channel information generator  38 , under the control of the controller  34 , can generate channel information or terminal information for the new PAN. 
         [0049]    According to another embodiment of the present invention, when terminal information for the node terminal  14  is previously stored in the memory  28 , the channel information generator  38  generates only the channel information. 
         [0050]    The controller  34  controls the overall operation of the mobile communication terminal  14 . According to an embodiment of the present invention the controller  34  controls the mobile communication terminal  14  to receive the content data broadcasted from the PAN formed by the coordinator terminal  10 . The controller  34  searches for PANs existing in the ZigBee network, when it intends to switch the PAN from which it receives content data. The controller  34  controls the display  26  to display the PAN search result, and can receive a user input for selecting any one of the displayed PANs by means of the key input unit  24 . 
         [0051]    Before closing the connection to the first PAN to connect with the second PAN, the controller  34  transmits channel information for the second PAN to the headset  18 . 
         [0052]    The headset  18  can determine to which PAN the mobile communication terminal  14  will connect, based on the channel information received from the mobile communication terminal  14 . When the connection between the first PAN and the mobile communication terminal  14  is closed, the headset  18  can easily find out the second PAN to which the mobile communication terminal  14  has connected, by accessing the PAN having a channel number and a PAN ID included in the channel information. Therefore, according to the present invention, the headset  18  has no need to access all channels in the ZigBee network and re-access every PAN included in each channel to determine the presence/absence of the mobile communication terminal  14  that should be connected to the headset  18 , on a one-by-one basis. 
         [0053]    After transmitting the channel information to the headset  18 , the controller  34  closes the connection with the first PAN, and accesses the second PAN. When the headset  18  accesses the second PAN and sends a Join Request (or Connect Request), the controller  34  reconnects with the headset  18  and transmits content data of the second PAN to the headset  18 . 
         [0054]    The headset  18 , which includes the ZigBee communication module  36  for ZigBee communication, receives the content data broadcasted from the first coordinator of the first PAN or the second coordinator of the second PAN through the mobile communication terminal  14 , and reproduces the received content data. 
         [0055]    According to an embodiment of the present invention, the headset  18  receives the channel information for the second PAN before the mobile communication terminal  14  switches from the first PAN to the second PAN. When the connection between the first PAN and the mobile communication terminal  14  is closed, the connection between the first PAN and the headset  18 , which was receiving content data through the mobile communication terminal  14 , is closed. Therefore, the headset  18  terminates its reproduction of the content data from the first PAN. When the connection between the mobile communication terminal  14  and the first PAN is closed, the headset  18  which was connected to the first PAN via the mobile communication terminal  14  detects the close of the connection between the first PAN and the mobile communication terminal  14 . The headset  18  can detect the closed connection between the first PAN and the mobile communication terminal  14  because as the mobile communication terminal  14  which was serving as a router of the headset  18  leaves the first PAN, the headset  18  also leaves the first PAN. 
         [0056]    According to another embodiment of the present invention, when the mobile communication terminal  14  was transmitting content data to the headset  18 , a coordinator of the first PAN is the mobile communication terminal  14 . In the ZigBee network, the mobile communication terminal  14  cannot simultaneously serve as a coordinator and a node. Therefore, the mobile communication terminal  14 , which was serving as the coordinator, should remove its formed first PAN in order to access another channel. Since the mobile communication terminal  14 , which was serving as the coordinator, has removed the PAN, the headset  18 , which was connected to the mobile communication terminal  14 , cannot receive the content data transmitted from the mobile communication terminal  14 . In addition, since the first PAN will be removed, the connection between the headset  18  and the first PAN is also automatically closed. 
         [0057]    According to another embodiment of the present invention, even when the mobile communication terminal  14  directly sends a connection close (or join close) command to the headset  18 , the connection between the headset  18  and the mobile communication terminal  14  is disconnected. 
         [0058]    The headset  18  accesses the second PAN based on the channel information. The channel information includes a channel number of the switched channel in which the second PAN is included, and a PAN ID of the second PAN. Before switching the PAN, the mobile communication terminal  14  can transmit the channel information to the headset  18  to previously notify that it will soon connect with the second PAN after closing the connection to the first PAN. 
         [0059]    Upon detecting the close of the connection between the mobile communication terminal  14  and the first PAN, the headset  18  determines, as a second PAN, the PAN whose channel number and PAN ID are equal to the channel number and the PAN ID included in the channel information, among the PANs registered in the ZigBee network. The headset  18  then accesses the second PAN. In this case, the headset  18  has already stored information on all the channels or PANs registered in the ZigBee network. 
         [0060]    The headset  18 , after accessing the second PAN, sends a Join Request to the mobile communication terminal  14  based on the terminal information for the mobile communication terminal  14 , and resumes the connection with the mobile communication terminal  14 . The terminal information on the mobile communication terminal  14 , includes a 64-bit address of the mobile communication terminal  14 . The terminal information can be transmitted from the mobile communication terminal  14  along with the channel information, or can be a value previously stored by the headset  18 . Each mobile communication terminal  14  has a 64-bit address as its own unique value. Therefore, the headset  18  can identify a desired mobile communication terminal  14  among the mobile communication terminals joined in the PAN or channel, using the 64-bit address of the terminal information. 
         [0061]    The headset  18  accesses the second PAN, transmits a Join Request message to the mobile communication terminal  14  having a 64-bit address being equal to the 64-bit address included in the terminal information, and receives a Join Confirm (or Connect Grant) message in response to the Join Request, making it possible to reconnect with the mobile communication terminal  14 . 
         [0062]    According to another embodiment of the present invention, the headset  18  can broadcast the 64-bit address of terminal information to all terminals joined in the second PAN along with the Join Request message, and wait for a Join Confirm message from the mobile communication terminal  14  for a predetermined time. Among the terminals receiving the broadcasted Join Request message, the mobile communication terminal  14  that should be reconnected to the headset  18  transmits a Join Confirm message to the headset  18 , thereby resuming the connection with the headset  18 . 
         [0063]      FIG. 3  is a signaling diagram illustrating a content data transmission/reception method in a ZigBee network system according to an embodiment of the present invention. 
         [0064]    It is assumed in the drawing that a mobile communication terminal  14  is previously connected to a first PAN, and a headset  18  receives content data broadcasted from the first PAN through the mobile communication terminal  14  and reproduces the received content data. 
         [0065]    A first coordinator, which has formed the first PAN, broadcasts content data (Step S 42 ), and the mobile communication terminal  14  receives the content data broadcasted from the first PAN and transmits the received content data to the headset  18  (Step S 44 ). The headset  18  reproduces the content data received through the mobile communication terminal  14  (Step S 46 ). 
         [0066]    The mobile communication terminal  14 , when it intends to switch the PAN from which it receives broadcast data, searches for PANs in the ZigBee network (Step S 48 ). 
         [0067]    The mobile communication terminal  14  selects a second PAN through a user input, and transmits channel information for the second PAN to the headset  18  (Step S 50 ). 
         [0068]    To access the second PAN, the mobile communication terminal  14  closes the connection with (or the join with) the first PAN (Step S 52 ), and sends a Join Request to the second PAN (Step S 54 ). The headset  18  accesses the second PAN based on the channel information (Step S 56 ), and sends a Join Request to the mobile communication terminal  14  (Step SS 8 ). The headset  18  accesses the second PAN by accessing the PAN whose channel number and PAN ID are identical to the channel number and PAN ID included in the channel information among the PANs registered in the ZigBee network. 
         [0069]    A second coordinator, which has formed the second PAN, broadcasts content data to the second PAN (Step S 60 ), and the mobile communication terminal  14  receives the content data broadcasted from the second PAN and transmits the received content data to the headset  18  (Step S 62 ). The headset  18  reproduces the content data received from the second PAN through the mobile communication terminal  14  (Step S 64 ). 
         [0070]      FIG. 4  is a flowchart illustrating a content data transmission/reception method of a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention. 
         [0071]    It is assumed in the drawing that the mobile communication terminal  14  has already connected with the first PAN. The mobile communication terminal  14  receives content data broadcasted from the first PAN, and delivers the received content data to the headset  18  in Step S 72 . The headset  18  reproduces the content data transmitted through the mobile communication terminal  14 . 
         [0072]    When it is desires to switch the PAN from which the mobile communication terminal  14  receives broadcast, searches for PANs in the ZigBee network in Step S 74 , and selects a second PAN from among the searched PANs in Step S 76 . 
         [0073]    The mobile communication terminal  14  can search for all PANs that broadcast the content data using the ZigBee communication module  30  in its current position. The selection of the PAN can be achieved through a user input. 
         [0074]    According to an embodiment of the present invention, the mobile communication terminal  14  can stop the transmission of the content data to the headset  18  to search for PANs. The ZigBee communication scheme is a low-power communication scheme, and in this scheme, the amount of communication between the PAN and the mobile communication terminal  14  is not great. When the mobile communication terminal  14  simultaneously performs the PAN search and the data transmission, its communication increases causing a possible overload. In addition, due to an increase in the amount of communication allocated to the mobile communication terminal  14 , data interruption may happen when the mobile communication terminal  14  transmits content data to the headset  18 . Therefore, the mobile communication terminal  14  stops the data transmission to the headset  18  to perform smooth communication. 
         [0075]    After selecting the second PAN in Step S 76 , the mobile communication terminal  14  transmits channel information for the second PAN to the headset  18  in Step S 78 . 
         [0076]    The channel information that the mobile communication terminal  14  transmits to the headset  18  is information indicating that the mobile communication terminal  14  will soon connect with the second PAN after closing the connection with the first PAN, and the channel information includes a channel number of the switched channel in which the second PAN is included, and a PAN ID of the second PAN. According to an embodiment of the present invention, the channel information can include configuration information containing a beacon period of the second PAN so that the headset  18  can easily access the second PAN. Upon receiving the channel information from the mobile communication terminal  14 , the headset  18  can perceive the PAN that the mobile communication terminal  14  will access after closing its connection with the first PAN. In addition, the headset  18  can simply find out the PAN to which the mobile communication terminal  14  has connected, using the channel information. As a result, it is possible to reduce the time required for finding out the PAN that the mobile communication terminal  14  has accessed. 
         [0077]    The mobile communication terminal  14  closes its connection with the first PAN and then accesses the second PAN in Step S 80 . When the mobile communication terminal  14  closes the connection with the first PAN, the headset  18 , which was receiving content data of the first PAN through the mobile communication terminal  14 , also closes its connection to the first PAN, so it cannot reproduce the content data of the first PAN. 
         [0078]    According to an embodiment of the present invention, the mobile communication terminal  14  can transmit a connection close command to the headset  18  to close the connection between the headset  18  and the first PAN. The mobile communication terminal  14  can transmit in Step S 78  the connection close command to the headset  18  along with the channel information to notify the headset  18  of the switching of the PAN. 
         [0079]    After accessing the second PAN in Step S 80 , the mobile communication terminal  14  maintains its connection to the second PAN, and when the headset  18  accesses the second PAN, the mobile communication terminal  14  receives a Join Request from the headset  18  that has accessed the second PAN in Step S 82 . When the mobile communication terminal  14  receives the Join Request from the headset  18  in Step S 82 , the connection between the headset  18  and the mobile communication terminal  14  is resumed. Upon receipt of the Join Request from the headset  18 , the mobile communication terminal  14  can transmit a Join Confirm message to the headset  18  to resume the connection with the headset  18 . 
         [0080]    After the connection of the mobile communication terminal  14  with the headset  18  is resumed in step S 82 , the mobile communication terminal  14  delivers the content data of the second PAN to the headset  18  (Step S 84 ). The headset  18  receives the content data of the second PAN through the mobile communication terminal  14  and reproduces the received content data. 
         [0081]      FIG. 5  is a flowchart illustrating a content data transmission/reception method of a headset in a ZigBee network system according to an embodiment of the present invention. 
         [0082]    It is assumed in the drawing that the mobile communication terminal  14  has accessed the first PAN, and transmits the content data broadcasted from the first PAN to the headset  18 . 
         [0083]    The headset  18  receives content data of the first PAN through the mobile communication terminal  14  and reproduces the received content data in Step S 92 . In the meantime, if the mobile communication terminal  14  intends to switch the PAN, it stops the data transmission to the headset  18  to smoothly search for PANs in the ZigBee network. 
         [0084]    When the mobile communication terminal  14  wishes to switch the content data from the first PAN to the second PAN, the headset  18  receives channel information for the second PAN from the mobile communication terminal  14  in Step S 94 . Then the headset  18  stops the reproduction of the content data broadcasted from the first channel in Step S 96 . The channel information can include therein a channel number of the switched channel in which the second PAN is included, and a PAN ID of the second PAN. 
         [0085]    Thereafter, the mobile communication terminal  14  closes the connection to the first PAN. The headset  18 , whose connection to both the mobile communication terminal  14  and the first PAN is closed, should be reconnected to the mobile communication terminal  14 . This is due to the fact that when a PAN is broadcasting content data in the private mode, the mobile communication terminal  14  or the headset  18  that has accessed the PAN cannot receive the broadcasted content data unless it undergoes a specific authentication procedure. 
         [0086]    The mobile communication terminal  14  can simply process the authentication procedure. However, the headset  18  has difficulty in processing the authentication procedure with the PAN since it has a simple structure compared with the mobile communication terminal  14 . Therefore, in the case where the PAN is in the private mode, the headset  18  accesses the PAN via the mobile communication terminal  14  and processes the authentication procedure. When the connection between the mobile communication terminal  14  and the PAN is closed, even the connection between the PAN and the headset  18 , which was connected thereto through the mobile communication terminal  14  in the private mode, is also automatically disconnected. In the private mode, the headset  18  should be reconnected to the mobile communication terminal  14  to process the authentication procedure. 
         [0087]    Even through there is no need for the authentication procedure as the PAN is in the public mode, the headset  18  should resume the connection with the mobile communication terminal  14 . The headset  18  can perform a call function in addition to the content data reproduction function, and the headset  18  cannot perform the call function unless it is connected to the mobile communication terminal  14 . Therefore, in the ZigBee network system according to an embodiment of the present invention, even when the headset  18  directly accesses the PAN and receives content data therefrom, it should keep the connection to the mobile communication terminal  10 . 
         [0088]    After transmitting the channel information to the headset  18 , the mobile communication terminal  14  accesses the second PAN. Since the mobile communication terminal  14  has accessed the second PAN, the headset  18  should access the second PAN and reconnect with the mobile communication terminal  14 . 
         [0089]    The headset  18  accesses the second PAN based on the channel information received in Step S 96  in Step S 98 . The method in which the headset  18  resumes the connection with the mobile communication terminal  14  connected to the second PAN in the ZigBee network will be described in detail with reference to  FIG. 6 . 
         [0090]    The headset  18 , which has accessed the second channel, sends a Join Request to the mobile communication terminal  14  joined in the second PAN (Step S 100 ). When the connection to the mobile communication terminal  14  is resumed, the headset  18  receives content data of the second PAN through the mobile communication terminal  14 , and reproduces the received content data in Step S 102 . 
         [0091]    According to another embodiment of the present invention, when the second PAN is in the public mode, the headset  18  can directly access the second PAN, receive content data therefrom, and reproduce the received content data. 
         [0092]      FIG. 6  is a flowchart illustrating a method for resuming a connection between a headset and a mobile communication terminal in a ZigBee network system according to an embodiment of the present invention. 
         [0093]    When the mobile communication terminal  14  closes its connection to the first PAN, the headset  18  also closes its connection with the first PAN in Step S 112 . Before closing the connection with the first PAN, the mobile communication terminal  14  transmits the channel information to the headset for the second PAN to which it will soon connect. The mobile communication terminal  14  transmits the channel information to the headset  18  on a unicast basis, and the transmitted channel information includes a channel number of the switched channel in which the second PAN is included, and a PAN ID of the second PAN. The term ‘unicast’ as used herein refers to a communication scheme for transmitting a data packet only to a particular recipient. 
         [0094]    The headset  18 , before Step S 112 , receives the channel information from the mobile communication terminal  14 . The headset  18  accesses the PAN whose channel information is equal to the channel information received from the mobile communication terminal  14  in Step S 114 . To this end, the headset  18  transmits to a coordinator of the second PAN a Join Request targeting the second PAN having the channel number and PAN ID included in the channel information. When the coordinator sends a response to the Join Request to the headset  18  within a predetermined time, the headset  18  is granted to access the second PAN, and otherwise, the headset  18  is granted to do so. 
         [0095]    Upon an access to the second PAN, the headset  18  broadcasts a Join Request to the mobile communication terminal whose terminal information is identical to the previously stored terminal information in Step S 116 . 
         [0096]    According to another embodiment of the present invention, the channel information can further include terminal information containing a 64-bit address of the mobile communication terminal  14 , together with the channel number of the switched channel and the PAN ID of the second PAN. The channel information including the terminal information is transmitted to the headset  18  before the mobile communication terminal  14  closes its connection with the first PAN. 
         [0097]    The mobile communication terminals  14  each have a different 64-bit address, so the 64-bit address is a unique value of the mobile communication terminal  14 . Therefore, the headset  18  can store therein the 64-bit address of the mobile communication terminal  14  to thereby identify the mobile communication terminal  14  that should resume the connection with the headset  18 . 
         [0098]    The headset  18  sends a Join Request to the mobile communication terminal  14  having a 64-bit address included in the terminal information among the 64-bit addresses of the mobile communication terminals connected to the second PAN, i.e., among the mobile communication terminals connected to the second PAN. The mobile communication terminal  14  receives the Join Request from the headset  18  and resumes its connection thereto. 
         [0099]    The headset  18  can transmit the Join Request to the mobile communication terminal  14  by broadcasting a Join Request message including a 64-bit address to the second PAN having a PAN ID included in the channel information. At least one terminal is connected to the second PAN accessed by the headset  18 . The at least one terminal includes the mobile communication terminal  14  that should resume the connection thereto. Upon receipt of the Join Request message, each terminal compares the 64-bit address included in the message with its own 64-bit address, and transmits a Join Confirm message to the headset  18  if they are identical to each other. Therefore, only the mobile communication terminal  14  that should be connected to the headset  18  responds to the Join Request from the headset  18 . 
         [0100]    Upon receiving the Join Confirm from the mobile communication terminal  14 , the headset  18  connects with the mobile communication terminal  14  (Step S 118 ). 
         [0101]      FIG. 7  is a diagram illustrating the PAN search result in a ZigBee network according to an embodiment of the present invention. 
         [0102]    The mobile communication terminal  14  can search for PANs in the ZigBee network, and display the search result on the display  26  of the mobile communication terminal  14 . The mobile communication terminal  14  can select any one of the searched PANs in response to the user input received. 
         [0103]    Shown in the drawing are  4  PANs  122 ,  124 ,  126  and  128  given as a result of the PAN search. In the drawing, a channel number and a PAN ID of each PAN are shown in the manner of “Channel Number/PAN ID.” 
         [0104]    ‘Latest Music’, ‘Old Pop Songs’, ‘Pentaport Rock Festival’ and ‘Christina Aguilera Live in Korea’ are broadcasted on CH. 11/3  122 , CH. 13/1  124 , CH. 23/2  126  and CH. 25/4  128 , respectively. The user selects/inputs his/her desired one of the displayed PANs by means of the key input unit  24 . 
         [0105]    For example, if the mobile communication terminal  14 , while receiving the broadcasted content data after being connected to CH.  11 / 3   122 , receives a user input for selecting CH. 25/4  126  by means of the key input unit  24 , it transmits channel information for CH. 25/4  126  to the headset  18  and then closes the connection with CH. 11/3  122 . 
         [0106]    As apparent from the foregoing description, the present invention provides a channel switching method for switching channels through which content data is received in a ZigBee network system capable of reducing the time for which the headset is reconnected to the mobile communication terminal, and a ZigBee network system thereof. 
         [0107]    According to an embodiment of the present invention, the mobile communication terminal can transmit channel information for the old PAN to the headset before switching to a new PAN, thereby allowing the headset to readily find out the new PAN. 
         [0108]    According to another embodiment of the present invention, the headset can simply find out the new PAN accessed by the mobile communication terminal based on the channel information received from the mobile communication terminal, thereby reducing the time required for finding out the PAN that the mobile communication terminal has accessed. 
         [0109]    According to a further embodiment of the present invention, the headset can reduce the time required for finding out the PAN that the mobile communication terminal has accessed, thereby reducing the time for which the reproduction of the content data broadcasted from the PAN is halted, and thus accommodating the user. 
         [0110]    While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.