Abstract:
There is provided a data transmitting system for transmitting data to be processed through a TCP/IP-based network. The data transmitting system includes a first device having an identification information obtaining system that transmits first data through the network using a first multicast address, and a data transmitting system that transmits the data to be processed through the network using a second multicast address. The data transmitting system further includes a second device having an identification information transmitting system that transmits second data containing the identification information of the second device through the network using a third multicast address, and a data receiving system that receives the data to be processed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a data transmitting system in which data to be processed is transferred from a client device to another device which has a function of processing the data.  
           [0002]    A network printing environment which enables a client computer to print out documents on one of printers connected to a network is widely known. In such a network environment, the client computer searches for the printers and sends printing data to the one of the printers according to a certain protocol such as TCP/IP (Transmission Control Protocol/Internet Protocol).  
           [0003]    Japanese Provisional Publication No. 2001-282488 discloses a network system in which a computer searches for printers connected to a network and sends printing data to one of the printers selected by a user.  
           [0004]    However, to use one of the printers on the above mentioned network printing environment, the user of the client computer is required to register IP addresses of the printers connected to the network so as to print out documents on one of the printers. It is very burdensome for the user to conduct such a setting up procedure of the IP address so as to print out documents.  
           [0005]    If a user who connects the user&#39;s computer to a network for the first time does not know IP addresses of printers connected the network, the user can not use the printers.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is advantageous in that it provides a data transmitting system in which a client device can transmit data to be processed to a target device without registering an IP address of the target device into the client device.  
           [0007]    According to an aspect of the invention, there is provided a data transmitting system for transmitting data to be processed through a TCP/IP-based network to which a plurality of devices including a first device and a second device are connected, the data to be processed being transmitted by the first device and received by the second device. The first device includes an identification information obtaining system that transmits first data through the network using a first address which does not specify a destination to obtain identification information of the plurality of devices except the first device. The second device includes an identification information transmitting system that transmits second data containing the identification information of the second device through the network using a second multicast address in response to the first data transmitted by the identification information obtaining system of the first device. The first device further includes a data transmitting system that transmits the data to be processed through the network using a third multicast address so that the data to be processed is received by the second device which is one of devices which transmit the identification information to the identification information obtaining system. The second device further includes a data receiving system that receives the data to be processed transmitted by the data transmitting system of the first device.  
           [0008]    With this configuration, since multicast addresses are used for transmitting the data to be processed form the first device to the second device, it is unnecessary to register an IP address of the second device into the first device. In a particular case, the first address may be a first multicast address. In a particular case, the first device may notify the second device of the second multicast address, and the identification information transmitting system of the second device uses the second multicast address notified by the first deice.  
           [0009]    Optionally, the first device may include a selecting system that selects one of the devices which transmit the identification information to the identification information obtaining system. In this case, the data transmitting system transmits the identification information of the selected one of the devices with the data to be processed through the network using the third multicast address. The selected one of the devices is the second device.  
           [0010]    Still optionally, the identification information obtaining system of the first device may incorporate the identification information of the first device into the first data, and the identification information transmitting system of the second device may incorporate the identification information of the first device contained in the first data into the second data.  
           [0011]    In a particular case, the identification information of the devices on the network may include at least one of a device name, location information, a MAC address and an IP address of a device on the network.  
           [0012]    In a particular case, the first multicast address, the third multicast address and the second multicast address may be different from each other. In a particular case, at least two of the first multicast address, the third multicast address and the second multicast address may be equal to each other.  
           [0013]    Optionally, all of the devices configured to be the second device on the network may receive data transmitted by using the first multicast address.  
           [0014]    Still optionally, part of the devices connected to the network may receive data transmitted by using the third multicast address.  
           [0015]    Still optionally, only the first device of the devices connected to the network may receive data transmitted by using the second multicast address. Still optionally, the data transmitting system may include an address determining system that determines the second multicast address.  
           [0016]    In a particular case, the data receiving system of the second device may transmit third data indicating an acknowledgement of receipt of the data to be processed when the data receiving system receives the data to be processed, the data receiving system transmitting the third data through the network using a fourth multicast address. In this case, the data transmitting system of the first device receives the third data transmitted by the data receiving system of the second device.  
           [0017]    Optionally, the data transmitting system may include an address determining system that determines the third multicast address and the fourth multicast address. In a particular case, the first device and the second device may join address groups whose addresses are determined by the address determining system.  
           [0018]    Optionally, the data transmitting system may include an address determining system that determines the third multicast address used for transmitting the data to be processed. In a particular case, the second device may join an address group whose address is determined by the address determining system.  
           [0019]    In a particular case, the first device may include the address determining system.  
           [0020]    Alternatively, the second device may include the address determining system.  
           [0021]    In a particular case, the second device may be a printer, and the data to be processed may be print data.  
           [0022]    According to another aspect of the present invention, there is provided a terminal device for transmitting data to be processed through a TCP/IP-based network to which a plurality of devices are connected. The terminal device includes an identification information obtaining system that transmits first data through the network using a first multicast address to obtain identification information of the plurality of devices on the network. The terminal device further includes a data transmitting system that transmits the data to be processed through the network using a second multicast address in order that the data to be processed is received by a requested device which is one of devices which transmit the identification information to the identification information obtaining system.  
           [0023]    With this configuration, multicast addresses are used for transmitting the data to be processed form the terminal device to the requested device, it is unnecessary to register an IP address of the requested device into the terminal device.  
           [0024]    Optionally, the terminal device may include a selecting system that selects one of the devices which transmit the identification information to the identification information obtaining system. In this case, the data transmitting system transmits the identification information of the selected one of the devices with the data to be processed through the network using the second multicast address. The selected one of the devices is the requested device.  
           [0025]    According to another aspect of the present invention, there is provided a terminal device for receiving data to be processed through a TCP/IP-based network to which a plurality of devices are connected. The terminal device includes an identification information transmitting system that transmits first data containing identification information of the terminal device through the network using a first multicast address in response to a request transmitted by a requesting device on the network, and a data receiving system that receives the data to be processed which is transmitted by the requesting device through the network using a second multicast address.  
           [0026]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the terminal device, it is unnecessary to register an IP address of the terminal device into the requesting device.  
           [0027]    According to another aspect of the present invention, there is provided a method of transmitting data to be processed through a TCP/IP-based network to which a plurality of devices including a requesting device and a requested device are connected, the data to be processed being transmitted by the requesting device and received by the requested device. The method includes transmitting from the requesting device a search packet through the network using a first multicast address so as to obtain identification information of the devices, and receiving at the requesting device the identification information transmitted by at least one of the plurality of devices using a second multicast address. The method further includes selecting one of devices whose identification information has been received, and transmitting from the requesting device the identification information of the selected one of the devices and the data to be processed through the network using a third multicast address.  
           [0028]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the requested device, it is unnecessary to register an IP address of the requested device into the requesting device.  
           [0029]    According to another aspect of the present invention, there is provided a method of transmitting data to be processed through a TCP/IP-based network to which a plurality of devices including a requesting device and a requested device are connected, the data to be processed being transmitted by the requesting device and received by the requested device. The method includes transmitting from the requesting device a search packet through the network using a first multicast address so as to obtain identification information of the devices, receiving at the requesting device the identification information transmitted by at least one of the plurality of devices using a second multicast address, and selecting one of devices whose identification information has been received. The method further includes transmitting from the requesting device the identification information of the selected one of the devices and the data to be processed through the network using a third multicast address, receiving an acknowledgement of receipt of the data to be processed transmitted by the requested device using a forth multicast address, and repeating the step of transmitting identification information and data to be processed and the step of receiving the acknowledgement of receipt until the data to be processed is completely transmitted.  
           [0030]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the requested device, it is unnecessary to register an IP address of the requested device into the requesting device.  
           [0031]    According to another aspect of the present invention, there is provided a method of receiving data to be processed through a TCP/IP-based network to which a plurality of devices including a requesting device and a requested device are connected, the data to be processed being transmitted by the requesting device and received by the requested device. The method includes receiving from the requesting device a search packet which is transmitted through the network using a first multicast address, transmitting identification information through the network using a second multicast address, and receiving from the requesting device the identification information of the requested device and the data to be processed which are transmitted through the network using a third multicast address.  
           [0032]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the requested device, it is unnecessary to register an IP address of the requested device into the requesting device.  
           [0033]    According to another aspect of the present invention, there is provided a method of receiving data to be processed through a TCP/IP-based network to which a plurality of devices including a requesting device and a requested device are connected, the data to be processed being transmitted by the requesting device and received by the requested device. The method includes receiving a search packet which is transmitted by the requesting device through the network using a first multicast address, transmitting identification information through the network using a second multicast address, and receiving the identification information of the requested device and the data to be processed which are transmitted by the requesting device through the network using a third multicast address. The method further includes transmitting an acknowledgement of receipt of the data to be processed using a forth multicast address when the data to be processed is received, and repeating the step of receiving the identification information and data to be processed and the step of transmitting the acknowledgement of receipt step until the data to be processed is completely received.  
           [0034]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the requested device, it is unnecessary to register an IP address of the requested device into the requesting device.  
           [0035]    According to another aspect of the present invention, there is provided a method of transmitting data to be processed through a TCP/IP-based network to which a plurality of devices including a requesting device and a requested device are connected, the data to be processed being transmitted by the requesting device and received by the requested device. The method includes transmitting a request for obtaining identification information of the plurality of devices except the requesting device from the requesting device through the network using a first address, receiving the request at the requested device, and transmitting the identification information from the requested device through the network using a second multicast address in reply to the request. The method further includes transmitting from the requesting device the identification information of the requested device and the data to be processed through the network using a third multicast address, and receiving the identification information and the data to be processed at the requested device.  
           [0036]    With this configuration, multicast addresses are used for transmitting the data to be processed form the requesting device to the requested device, it is unnecessary to register an IP address of the requested device into the requesting device.  
           [0037]    The device and method according to the present invention can be realized when appropriate programs are provided and executed by a computer. Such programs may be stored in recording medium such as a flexible disk, CD-ROM, memory cards and the like and distributed. Alternatively or optionally, such programs can be distributed through networks such as the Internet. 
       
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0038]    [0038]FIG. 1 shows a network configuration to which an embodiment of the present invention is applied; and  
         [0039]    [0039]FIG. 2A is a block diagram of a personal computer connected to a network shown in FIG. 1;  
         [0040]    [0040]FIG. 2B is a block diagram of a printer connected to the network shown in FIG. 1;  
         [0041]    [0041]FIG. 3 is a sequence diagram illustrating a data transfer process between the personal computer and the printer;  
         [0042]    [0042]FIG. 4 is a flow chart illustrating a print data transfer process executed on the personal computer;  
         [0043]    [0043]FIG. 5 is a flowchart illustrating the data transfer process executed on the printer;  
         [0044]    [0044]FIG. 6 is a flowchart illustrating a multicast print task executed by the printer;  
         [0045]    [0045]FIG. 7 shows an example of a selection screen;  
         [0046]    [0046]FIG. 8 shows a packet format of a search packet created by the personal computer;  
         [0047]    [0047]FIG. 9 shows a packet format of a reply packet created by the printer;  
         [0048]    [0048]FIG. 10 shows a packet format of a join request packet;  
         [0049]    [0049]FIG. 11 shows a packet format of a leave request packet;  
         [0050]    [0050]FIG. 12A shows a packet formats of a join success reply packet;  
         [0051]    [0051]FIG. 12B shows a packet format of a join unsuccess reply packet;  
         [0052]    [0052]FIG. 13 shows a packet format of a leave reply packet;  
         [0053]    [0053]FIG. 14 shows a packet format of a print data packet; and  
         [0054]    [0054]FIG. 15 shows a packet format of an ACK packet; 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0055]    Hereafter, an embodiment of the invention is described with reference the accompanying drawings.  
         [0056]    [0056]FIG. 1 shows a network configuration to which an embodiment of the present invention is applied. As shown in FIG. 1, a data transfer system  1  has a personal computer (PC)  2 , five printers  3  ( 3   a - 3   e ), and a router  4  which are connected to each other via a network  5  such as a LAN (Local Area Network) or a wireless LAN.  
         [0057]    [0057]FIGS. 2A and 2B show block diagrams of the PC  2  and the printer  3 , respectively.  
         [0058]    As shown in FIG. 2A, the PC  2  has a CPU (Central Processing Unit)  21 , a ROM (Read Only Memory)  22 , a RAM (Random Access Memory)  23 , an HDD (Hard Disc Device)  24 , an operation unit  25 , a display unit  26  and a LAN interface (LAN I/F)  27  which are connected to each other.  
         [0059]    The CPU  21  executes various computer programs stored in the ROM  22  or the HDD  24 . The ROM  22  constitutes a part of a main memory of the PC  2 , and stores various programs for example a system program.  
         [0060]    Similarly to the ROM  22 , the RAM  23  constitutes a part of the main memory of the PC  2 . The RAM  23  has a work area in which intermediate results of processes executed by the CPU  21  are stored. In the HDD  24 , various programs, for example, a program for a data transfer process shown in FIG. 4, are stored.  
         [0061]    The operation unit  25  is an interactive input device such as a keyboard or a mouse. The display unit  24  which displays various types of information is, for example, a liquid crystal display. The LAN I/F  27  enables the PC  2  to communicate with the printer  3  through the network  105 .  
         [0062]    As shown in FIG. 2B, the printer  3  has a CPU (Central Processing Unit)  31 , a ROM (Read Only Memory)  32 , a RAM (Random Access Memory)  33 , an EEPROM (Electrically Erasable Programmable Read Only Memory)  34 , an operation unit  35 , a display unit  36 , a printing unit  37  and a LAN interface (LAN I/F)  38  which are connected to each other.  
         [0063]    The CPU  31  executes various programs stored in the ROM  32 . The ROM  32  constitutes a part of a main memory of the printer  3 , and stores various programs for example a system program.  
         [0064]    Similarly to the ROM  32 , the RAM  33  constitutes a part of the main memory of the printer  3 . The RAM  33  has a work area in which intermediate results of processes executed by the CPU  31  are stored. In the EEPROM  34 , various programs, for example, a program for the data transfer process shown in FIGS. 5 and 6, are stored.  
         [0065]    The operation unit  35  is an interactive input device such as a keyboard or a touch panel placed on the display unit  36 . The display unit  36  which displays various types of information is, for example, a liquid crystal display. The printing unit  37  prints text or images transmitted from the PC  2  in color or monochrome on print media. The LAN I/F  38  enables the printer  3  to communicate with other devices such as the PC  2  through the network  5 .  
         [0066]    Hereafter, the data transfer process will be described with reference to sequence diagrams of FIGS.  3 - 7  and FIGS.  12 - 19  which shows packet formats of packets used in the data transfer process.  
         [0067]    [0067]FIG. 3 is a sequence diagram illustrating a data transfer process between the PC  2  and the printer  3 . As shown in FIG. 3, firstly, the PC  2  transmits a search packet  51  for searching for the printer  3  and receives a search reply packet  52  including address information of the printer  3 . To search for the printer  3  on the network  5 , the CPU  21  of the PC  2  transmits the search packet  51  using a Multicast IP address M 1  so that the search packet  51  can be received by one or more devices (i.e., the printers  3   a - 3   e ) connected to the network  5 .  
         [0068]    A packet format of the search packet  51  created by the PC  2  is shown in FIG. 8. Although each packet (i.e., TCP packet) that the PC  2  or the printer  3  transmits includes an Ethernet header, an IP header in which the Multicast IP address is contained, a TCP header and a data portion, each packet format shown in FIGS.  12 - 19  indicates only data portion of the TCP packet for the sake of simplicity.  
         [0069]    As shown in FIG. 8, the search packet  51  (i.e., the data portion of the search packet  51 ) includes four fields: a destination address field  51   a , a source address field  51   b , a packet type field  51   c , and a field of a multicast address for receipt of search reply  51   d . Six byte data “FF FF FF FF FF FF” in the destination address field  51   a  indicates that the search packet  51  is a broadcast packet.  
         [0070]    In the source address field  51   b , a MAC (Media Access Control) address of a sending device (i.e., the PC  2 ) is contained. In the packet type field  51   c , a 2 byte code which indicates the packet  51  is the search packet is contained. This 2 byte code indicates, for example, a command “SEARCH”. In the field  51   d , a Multicast address M 3  for receipt of a reply packet  52  is designated.  
         [0071]    As shown in FIG. 3, the printer  3  transmits a reply packet  52  to the PC  2  in reply to the search packet  51  using the Multicast IP address M 3 .  
         [0072]    A packet format of the reply packet  52  created by the printer  3  is shown in FIG. 9. As shown in FIG. 9, the reply packet  52  includes a destination address field  52   a , a source address field  52   b , and a packet type field  52   c . In the destination address field  52   a , a MAC address of the sending device of the search packet  51 (i.e., the MAC address of the PC  2 ), is contained. In the source address field  52   b , a MAC address of a sending device of the reply packet  52  (i.e., the MAC address of the printer  3 ) is contained. In the packet type field  52   c , a 2 byte code which indicates the packet  52  is the reply packet is contained. This 2 byte code indicates, for example, a command “SEARCHREPLY”.  
         [0073]    The reply packet  52  further includes a model name length field  52   d , a model name field  52   e , a location length field  52   f  and a location field  52   g . In the model name length field  52   d  and the model name field  52   e , a model name length of the sending device (i.e., the model name length of the printer  3 ) and a model name of the sending device (i.e., the model name of the printer  3 ) are contained, respectively.  
         [0074]    In the location length field  52   f  and the location field  52   g , the number of bytes of location information in the location field  52   g , and the location information of the sending device (i.e., the printer  3 ) are contained, respectively. After the communication process shown in FIG. 3 is completed, the PC  2  can show on the display unit  26  a selection screen  26   a  including a list of the printers  3  that have replied to the search packet  51 .  
         [0075]    [0075]FIG. 7 shows an example of the selection screen  26   a . In the selection screen  26   a , model names and locations of the printers are indicated. The user can select one of the printers from the list. To select a target printer, the user firstly moves a hatching indication  26   f  by clicking a button  26   c  or a button  26   d  using the mouse to a position of the target printer and secondly clicks an OK button  26   b.    
         [0076]    As shown in FIG. 3, after the PC  2  receives the reply packet  52 , the PC  2  transmits a join request packet  53  to one of the printers  3  selected from the list of printers  3 , shown in the selection screen  26   a , that have replied to the search packet  51 . The join request packet  53  is a packet that requests the selected printer to join a print multicast group in which the PC  2  and the printer  3  (which has decided to join the print multicast group) communicate with each other using Multicast IP addresses specific to the print multicast group.  
         [0077]    As shown in FIG. 10, the join request packet  53  (i.e., the data portion of the packet  53 ) includes a destination address field  53   a , a source address field  53   b , and a packet type field  53   c.    
         [0078]    In the destination address field  53   a , a MAC address of the printer selected from the list displayed on the display unit  26  is contained. In the source address field  53   b , a MAC address of a sending device of the packet  53  (i.e., the MAC address of the PC  2 ) is contained. In the packet type field  51   c , a 2 byte code which indicates the packet  53  is the join request packet is contained. This 2 byte code indicates, for example, a command “JOIN”.  
         [0079]    After reception of the join request packet  53 , the selected printer determines whether it is possible to join a print multicast group. When the printer can join the print multicast group, the selected printer transmits a join success reply packet  55  to the PC  2  in reply to the join request packet  53  using a Multicast IP address M 3  (see FIG. 3). On the other hand, when the printer has already joined another print multicast group, the printer transmits a join unsuccess reply packet  56  to the PC  2  in reply to the join request packet  53  using a Multicast IP address M 3  (see FIG. 3).  
         [0080]    [0080]FIG. 12A shows a packet formats of the join success reply packet  55 . The packet  55  includes a destination address field  55   a , a source address field  55   b , and a packet type field  55   c . In a destination address field  55   a , a MAC address of a sending device of the join request packet  52  (i.e., the MAC address of the PC  2 ) is contained. In the source address field  55   b , a sending device of this packet  53  (i.e., the MAC address of the selected printer) is contained. In the packet type field  55   c , a 2 byte code indicating that the selected printer successfully joins the print multicast group is contained. This 2 byte code indicates, for example, a command “JOINOK”.  
         [0081]    The join success packet  55  further includes a data receiving multicast address field  55   d  and an ACK transmitting multicast address field  55   e . In the data receiving multicast address field  55   d , the selected printer designates a Multicast IP address (for example, M 2 ) for receiving a print data packet  58 . In the ACK transmitting multicast address field  55   e , the selected printer designates a Multicast IP address (for example, M 4 ) for transmitting an ACK packet  59 .  
         [0082]    [0082]FIG. 12B shows a packet format of the join unsuccess reply packet  56 . As shown in FIG. 12B, the packet  56  includes a destination address field  56   a , a source address field  56   b , and a packet type field  56   c . In the destination address field  56   a , a MAC address of a sending device of the join request packet  52  (i.e., the MAC address of the PC  2 ) is contained. In the source address field  56   b , a sending device of this packet  56  (i.e., the MAC address of the selected printer) is contained. In the packet type field  56   c , a 2 byte code indicating that the selected printer has already joined another print multicast group is contained. This 2 byte code indicates, for example, a command “JOINNG”.  
         [0083]    As shown in FIG. 3, after the PC  2  receives the join success reply packet  55  from the printer  3 , the PC  2  transmits print data to the printer. The PC  2  firstly transmits a print data packet  58  containing print data to the printer using a Multicast IP address M 2  designated by the printer. Then, the PC  2  waits for an ACK (acknowledgement) packet  59  which the printer transmits using a Multicast IP address M 4 . When the PC  2  receives the ACK packet  59 , the PC  2  transmits a next print data packet  58 . By repeating transmission of the print data packet  58  and reception of the ACK packet, the print data is completely transmitted from the PC  2  to the printer. Since size of a print data area  58   e  of the print data packet  58  (see FIG. 14), the print data is transferred in units of 512 bytes.  
         [0084]    [0084]FIG. 14 shows a packet format of the print data packet  58 . As shown in FIG. 14, the print data packet  58  includes a destination address field  58   a , a source address field  58   b  and a packet type field  58   c . In the destination address field  58   a , a MAC address of the printer which has sent the join success packet  55  back to the PC  2  is contained. In the source address field  58   b , a MAC address of a sending device of the print data packet  58  (i.e., the MAC address of the PC  2 ) is contained. In the packet type field  56   c , a 2 byte code indicating that the packet  58  is the print data packet. This 2 byte code indicates, for example, a command “PRINTDATA”.  
         [0085]    The print data packet  58  further includes a sequence number field  58   d  and a print data area  58   e . In the sequence number field  58   d , the PC  2  designates a sequence number of the print data packet  58  is contained. In the print data area  58   e , a portion of the print data (i.e., 512 bytes data) is contained. If a total size of the print data is an integral multiple of 512 bytes, the print data area  58   e  of the last print data packet  58  is all zero.  
         [0086]    [0086]FIG. 15 shows a packet format of the ACK packet  59 . As shown in FIG. 15, the ACK packet  59  includes a destination address field  59   a , a source address field  59   b , a packet type field  59   d  and a sequence number field  59   e . In the destination address field  59   a , a MAC address of a sending device of the print data packet  58  (i.e., the MAC address of the PC  2 ) is contained. In the source address field  59   b , a MAC address of a sending device of this packet  59  (i.e., the MAC address of the printer) is contained.  
         [0087]    In the packet type field  59   c , a 2 byte code indicating that the sending device of this packet  59  (i.e., the printer) has successfully received the print data packet  58 . This 2 byte code indicates, for example, a command “PRINTDATAACK”. In the sequence number field  59   c , the same number as the sequence number of the print data packet  58  which the printer has most recently received.  
         [0088]    As shown in FIG. 3, after the print data has completely transferred to the printer, the PC  2  transmits a leave request packet  54  to the printer using the Multicast IP address M 1  (or M 2 ) so as to request the printer to leave the print multicast group. Then, the printer transmits a leave reply packet  57  to the PC  2  using a Multicast IP address M 3  in reply to the leave request packet  54 .  
         [0089]    [0089]FIG. 11 shows a packet format of the leave request packet  54 . As shown in FIG. 11, the packet  54  includes a destination address field  54   a , a source address field  54   b  and a packet type field  54   c . In the destination address field  54   a , a MAC address of the printer which the PC  2  requests to leave the print multicast group is contained. In the source address field  54   b  , a MAC address of a sending device (i.e., the MAC address of the PC  2 ) is contained. In the packet type field  54   c , a 2 byte code indicating that this packet  54  is the leave request packet. This 2 byte code indicates, for example, a command “LEAVE”.  
         [0090]    [0090]FIG. 13 shows a packet format of the leave reply packet  57 . As shown in FIG. 13, the leave reply packet  57  includes a destination address field  57   a , a source address field  57   b  and a packet type field  57   c . In the destination address field  57   a , a MAC address of the sending device of the leave request packet  54  (i.e., the MAC address of the PC  2 ) is contained. In the source address field  57   b , a MAC address of a sending device of this packet  57  (i.e., the MAC address of the printer) is contained. In the packet type field  57   c , a 2 byte code indicating that the printer has successfully leaved the print multicast group. This 2 byte code indicates, for example, a command “LEAVEOK”.  
         [0091]    The Multicast IP addresses used in the communication process shown in FIGS.  3 - 7  are summarized as follows.  
         [0092]    (1) Multicast IP address M 1  is used to transmit the search packet  51 , the join request packet  53 , and the leave request packet  54  to all of the printers connected to the network  5 . All of the printers  3  ( 3   a - 3   e ) receive and analyze packets having the Multicast IP address M 1 . In this embodiment, a broadcast address or one of various types of multicast IP addresses may be used as the address M 1 , so that all of the printers  3  ( 3   a - 3   e ) can receive the search packet  51 . In order that the printer  3  may receive the packet having the address M 1 , the address M 1  may be preset to the printer  3  by an administrator of the printer  3  or by a vendor of the printer  3 .  
         [0093]    (2) Multicast IP addresses M 2  and M 4  are used in the print multicast group. As described above, in the example of FIG. 3, the printer assigns the addresses M 4  and M 2  to the print data packet  58  and the ACK packet  59 , respectively. It should be noted that since the addresses M 2  and M 4  are only used by devices joined the print multicast group, all of the printers connected to the network  5  are not required to receive the packet having the Multicast IP address M 2 . The PC  2  receives all packets having the Multicast IP address M 4  .  
         [0094]    (3) Multicast IP address M 3  is used to transmit the reply packet  52 , the join success reply packet  55 , a join unsuccess reply packet  56 , and the leave reply packet  57 . The PC  2  receives all packets having the Multicast IP address M 3 .  
         [0095]    Although a multitude of IP addresses can be used as multicast IP addresses, it is preferable that IP addresses between 239.192.0.0-239.192.255.255 are used as the multicast IP addresses M 1 -M 4 .  
         [0096]    Next, the data transfer process will be described in detail with reference to FIGS.  8 - 10 .  
         [0097]    [0097]FIG. 4 is a flow chart illustrating the print data transfer process executed on the PC  2 . As shown in FIG.  4 , firstly, the CPU  21  of the PC  2  determines the multicast IP address M 3  on a random basis (S 100   a ), and then joins a multicast group M 1 /M 3  (S 100   b ). Next, the CPU  21  creates the search packet  51  and transmits it to the network  5  using the Multicast IP address M 1  (S 101 ). In step S 102 , the CPU  21  determines whether a predetermined time (for example,  5  seconds) has elapsed after the CPU  21  transmitted the search packet  51 .  
         [0098]    When the CPU  21  determined that the predetermined time has not elapsed (S 102 :NO), the CPU  21  repeats the step S 102 . When the CPU  21  determined that the predetermined time has elapsed (S 102 :YES), the CPU  21  determines whether the reply packet  52  addressed to the PC  2  (S 103 ) is received. More specifically, in step S 103 , the CPU  21  receives all packets having the Multicast IP address M 3  and analyses the received packets. If the received packet has the destination address  52   a  equal to the MAC address of the PC  2  and the packet type  52   c  indicates the reply packet, then it is determined that the CPU  21  receives the search reply packet  52 .  
         [0099]    When the CPU  21  determines that the reply packet  52  addressed to the PC  2  is not received (S 103 :NO), control proceeds to step S 104  where the CPU  21  displays error messages on the display unit  26 . Then, the data transfer process terminates.  
         [0100]    When the CPU  21  determines that at least one reply packet  52  is received (S 103 :YES), the CPU  21  displays the selection screen  26   a  based the model name fields  52   e  and location fields  52   e  of the received reply packets  52  (see FIG. 7). Next, the CPU  21  waits until the user selects a printer from the list of the selection screen  26   a  (S 106 ).  
         [0101]    When the user selects the printer, the CPU  21  transmits the join request packet  53  to the network  5  using the Multicast IP address M 1  (S 107 ) so as to request the selected printer to join a print multicast group. The CPU  21  writes the MAC address of the selected printer and the MAC address of the PC  2  in the destination address filed  53   a  and the source address field  53   b , respectively. Further, the CPU  21  writes the 2 byte code indicating the join request packet into the packet type field  53   c.    
         [0102]    In step S 108 , the CPU  21  waits for a packet. Next, in step S 109 , the CPU  21  determines whether the packet is received through the LAN I/F  27  within a predetermined time period (for example, 5 seconds). When the CPU  21  determines that the packet is not received within the predetermined tome period (S 109 :NO), the CPU  21  displays error messages on the display unit  26  (S 110 ). Then, the data transfer process terminates. When the CPU  21  determines that the packet is received within the predetermined time period (S 109 :YES), the CPU  21 , control proceeds to step S 111 .  
         [0103]    In step S 111 , the CPU  21  determines whether the selected printer has already joined another print multicast group. More specifically, if the packet received at step S 108  has the destination address equal to the MAC address of the PC  2 , the source address equal to the MAC address of the selected printer, and the packet type indicating the join unsuccess reply packet, the CPU determines that the selected printer has already joined another print multicast group and therefore the selected printer can not be used.  
         [0104]    It is appreciated that, in step S 111 , the CPU  21  is not necessarily required to check the source address field  56   b  because, typically, only the selected printer transmits the join unsuccess reply packet  56 .  
         [0105]    When the CPU  21  determines that the selected printer has already joined another print multicast group S 111 :YES), the CPU  21  display error message on the display unit  26  (S 112 ). Then, the data transfer process terminates. When the CPU  21  determines that the selected printer has not already joined another print multicast group S 111 :NO), control proceeds to step S 113 .  
         [0106]    In step S 113 , the CPU  21  determines whether the selected printer has successfully joined the print multicast group. More specifically, if the received packet S 108  has the destination address equal to the MAC address of the PC  2 , the source address equal to the MAC address of the selected printer, and the packet type indicating the join success reply packet, then the CPU  21  determines that the selected printer has successfully joined the print multicast group.  
         [0107]    It is appreciated that, in step S 113 , the CPU  21  is not necessarily required to check the source address field  55   b  because, typically, only the selected printer transmits the join success reply packet  55 .  
         [0108]    When the CPU  21  determines that the selected printer has not successfully joined the print multicast group (S 113 :NO), the CPU  21  display error message on the display unit  26  (S 114 ). Then, the data transfer process terminates. When the CPU  21  determines that the selected printer has successfully joined the print multicast group (S 114 :YES), control proceeds to step S 113   a.    
         [0109]    In step S 113   a , the PC  2  checks the data receiving multicast address field  55   d  of the join success reply packet  55  so as to recognize the Multicast IP address to be used for the print multicast group. Since in this embodiment the multicast IP addresses designated for the print multicast group are the addresses M 2  and M 4 , hereafter the print multicast group is referred to as a print multicast group M 2 /M 4 .  
         [0110]    Next, the CPU  21  resets a variable “SEQ” (assigns 1 to the SEQ) (S 115 ). In step S 116 , the CPU  21  determines whether size of remaining print data is less than 512 bytes. When the CPU  21  determines that size of remaining print data is not less than 512 bytes (S 116 :NO), control proceeds to step S 117 . When the CPU  21  determines that size of remaining print data is less than 512 bytes (or equal to zero byte) (S 116 :YES), control proceeds to step S 121 .  
         [0111]    In step S 117 , the CPU  21  creates the print data packet  58  and transmits it to the network  5  using the Multicast IP address M 2 . The CPU  21  writes the MAC address of the selected printer into the destination address field  58   a , the MAC address of the PC  2  into the source address field  58   b , and the 2 byte code indicating the print data packet into the packet type field  58   c . Further, The CPU  21  writes a value of the SEQ (i.e., the sequence number of the current print data packet) into the sequence number field  58   d  and 512 bytes print data into the print data area  58   e.    
         [0112]    Next, the CPU  21  waits for the ACK packet  59  (S 118 ). In step S 119 , the CPU  21  determines whether the ACK packet  59  is received through the LAN I/F  27  within a predetermined time period (for example, 5 seconds). More specifically, the CPU determines that the ACK packet  59  is received if the received packet has the destination address equal to the MAC address of the PC  2 , the source address equal to the MAC address of the selected printer, the packet type indicating the acknowledgement of the print data, and the sequence number equal to the sequence number of the print data packet transmitted in step S 117 .  
         [0113]    It is appreciated that, in step S 119 , the CPU  21  is not necessarily required to check the source address field  59   b  because, typically, only the selected printer transmits the ACK packet  59 .  
         [0114]    When the CPU  21  determines that the ACK packet  59  is not received within the predetermined time period (S 119 :NO), control returns to step S 116  to retransmit the 512 bytes print data. When the CPU  21  determines that the ACK packet  59  is received within the predetermined time period S 119 :YES), the CPU  21  increments the SEQ (S 120 ). Then, control returns to S 116  to repeat steps S 116 -S 120  with regard to remaining print data. The steps S 116 -S 120  are repeated until the size of the remaining print data becomes less than 512 bytes (or becomes zero byte).  
         [0115]    In step S 121 , the CPU  21  transmits the print data packet  58  containing all of the remaining print data. In step S 123 , the CPU  21  waits for the ACK packet  59 .  
         [0116]    In step S 123 , the CPU  21  determines whether the ACK packet  59  is received with a predetermined time period (for example, 5 seconds) in the same manner as the step S 119 . When the CPU  21  determines that the ACK packet  59  is not received within the predetermined time period (S 123 :NO), control returns to step S 121  to retransmits the print data. When the CPU  21  determines that the ACK packet  59  is received within the predetermined time period (S 123 :YES), control proceeds to step S 124 .  
         [0117]    Since all the print data is completely transmitted to the selected printer, in step S 214 , the CPU  21  transmits the leave request packet  54  to the network  5  using the Multicast IP address M 1 . The CPU  21  writes the MAC address of the selected printer into the destination address field  54   a , the MAC address of the PC  2  into the source address field  54   b , and the 2 byte code indicating the leave request packet into the packet type field  54   c.    
         [0118]    In step S 125 , the CPU  21  waits for the leave reply packet  57 . In step S 126 , the CPU  21  determines whether the selected printer has successfully leaved the print multicast group M 2 /M 4 . More specifically, the CPU  21  determines that the selected printer successfully leave the print multicast group M 2 /M 4  if the CPU receives the leave reply packet  57  which has the destination address equal to the MAC address of the PC  2 , the source address equal to the MAC address of the selected printer, and the packet type indicating the leave reply packet.  
         [0119]    It is appreciated that, in step S 126 , the CPU  21  is not necessarily required to check the source address field  57   b  because, typically, only the selected printer transmits the leave reply packet  57 .  
         [0120]    When the CPU  21  determines that the selected printer has not leaved the print multicast group M 2 /M 4  (S 126 :NO), the CPU  21  displays error messages on the display unit  26 . Then, the CPU  21  leaves the print multicast group M 2 /M 4  (S 128 ), and the data transfer process terminates. When the CPU  21  determines that the selected printer has successfully leaved the print multicast group (S 126 :YES), the CPU  21  leaves the print multicast group M 2 /M 4  (S 128 ). Then, the data transfer process terminates.  
         [0121]    [0121]FIG. 5 is a flowchart illustrating the data transfer process executed on the printer  3 . As shown in FIG. 5, initially, the CPU  31  of the printer  3  joins the multicast group M 1  (S 200 ). Then, the CPU  31  waits for a packet (S 201 ). When the CPU  31  receives the packet through the LAN I/F  38 , control proceeds to step S 202  where the CPU  31  determines whether the destination address designated in the received packet is equal to “FF FF FF FF FF FF” (which indicates the broadcast packet) or equal to the MAC address of the printer  3 .  
         [0122]    When the destination address of the received packet is not “FF FF FF FF FF FF” and the MAC address of the printer  3  (S 202 :NO), control returns to step S 201  to wait for a next packet. When the destination address of the received packet is “FF FF FF FF FF FF” or the MAC address of the printer  3  (S 202 :YES), control proceeds to step S 203 .  
         [0123]    In step S 203 , the CPU  31  further determines whether the received packet is the search packet  51  according to the 2 byte code in the packet type filed of the received packet.  
         [0124]    When the CPU  31  determines that the received packet is the search packet (S 203 :YES), the CPU  31  transmits the reply packet  52  to the network  5  using the Multicast IP address M 3  (S 204 ), and then the CPU  31  joins a multicast group M 3  (S 204   a ). In step S 204 , the CPU  31  writes the MAC address of the sending device of the search packet  51  (i.e., the MAC address of the PC  2 ) into the destination address field  52   a , and the MAC address of the printer  3  into the source address field  52   b . Further, the CPU  31  writes the 2 byte code indicating the search reply packet into the packet type field  52   c , the length of the model name into the model name length filed  52   d , the model name of the printer  3  into the model name field  52   e , the length of the location field into the location length field  52   f , and the location of the printer  3  into the location field  52   g.    
         [0125]    When the CPU  31  determines that the received packet is not the search packet (S 203 :YES), the CPU  31  then determines whether the received packet is the join request packet  53  according to the packet type field of the received packet. When the CPU  31  determines that the received packet is the join request packet  53  (S 205 :YES), control proceeds to step S 206 . When the CPU  31  determines that the received packet is not the join request packet  53  (S 205 :NO), control proceeds to step S 211 .  
         [0126]    In step S 206 , the CPU  31  determines whether the printer  3  has already joined another print multicast group. When the printer  3  has already joined another print multicast group (S 206 :YES), the CPU  31  transmits the join unsuccess reply packet  56  to the network  5  using the Multicast IP address M 3  (S 210 ). The CPU  31  writes the MAC address of the sending device of the join request packet  53  (i.e., the MAC address of the PC  2 ) into the destination address field  56   a , the MAC address of the printer  3  into the source address field  56   b , and the 2 byte code indicating the join unsuccess reply packet into the packet type field  56   c . Then, control returns to step S 201  to wait for a next packet.  
         [0127]    When the printer  3  has not joined another print multicast group (S 206 :NO), the CPU  31  determines two Multicast IP addresses to use the print multicast group on a random basis (S 206   a ). As described above, in this embodiment, the two addresses determined by the printer  3  for the print multicast group are M 2  and M 4 .  
         [0128]    In step S 207 , the CPU  31  determines to join the print multicast group M 2 /M 4 . Next, the CPU  31  initiates a multicast print task shown in FIG. 6 (S 208 ).  
         [0129]    In step S 209 , the CPU  31  transmits the join success reply packet  55  to the network  5  using the Multicast IP address M 3 . The CPU  31  writes the MAC address of the sending device of the join request packet  53  (i.e., the MAC address of the PC  2 ) into the destination address field  55   a , the MAC address of the printer  3  into the source address field  55   b , and the 2 byte code indicating the join success reply packet into the packet type field  55   c . The CPU  31  further writes the address M 2  into the data receiving multicast address field  55   d , and the address M 4  into the ACK transmitting multicast address field  55   e.    
         [0130]    In step S 211 , the CPU  31  determines whether the received packet is the leave request packet  54  according to the packet type field of the received packet. When the received packet is not the leave request packet  54  (S 211 :NO), since the received packet dos not relates to the data transfer process, the CPU  31  performs other process according to the received packet (S 215 ). Then, control returns to step S 201 .  
         [0131]    When the received packet is the leave request packet  54  (S 211 :YES), the CPU  31  leaves the print multicast group M 2 /M 4 /M 3  (i.e., the CPU  31  determines not to receive the packets having the Multicast IP address M 2 ) (S 212 ). Then, the terminates the multicast print task initiated in step S 208  (S 213 ).  
         [0132]    In step S 214 , the CPU  31  transmits the leave reply packet  57  to the network  5  using the Multicast IP address M 3 . The CPU  31  writes the MAC address of the sending device of the leave request packet  54  (i.e., the MAC address of the PC  2 ) into the destination address field  57   a , the MAC address of the printer  3  into the source address field  57   b , and the 2 byte code indicating the leave reply packet into the packet type field  57   c . Then, control returns to step S 201 .  
         [0133]    Next, the multicast print task initiated in step S 207  of FIG. 5 will be described with reference to FIG. 6. FIG. 6 is a flowchart illustrating the multicast print task. Firstly, the CPU  31  assigns zero to a variable SEQ (S 301 ). In step S 302 , the CPU  31  waits for the print data packet  58 .  
         [0134]    In step S 303 , the CPU  31  determines whether the print data packet  58  (which is transmitted from the PC  2  in step S 117  or S 121  in FIG. 4) is addressed to its own address. The CPU  31  determines that the received packet  58  is addressed to its own address if the destination address  58   a  is equal to the MAC address of the printer  3 .  
         [0135]    When the CPU  31  determines that the print data packet  58  is not addressed to its own address (S 303 :NO), control returns to step S 302  to wait for a next packet. When the CPU  31  determines that the print data packet  58  is addressed to its own address (S 303 :YES), control proceeds to step S 304 .  
         [0136]    In step S 304 , the CPU  31  determines whether the number in the sequence number field  58   d  of the received print data packet is smaller than or equal to the value of the variable SEQ. When the number in the sequence number field  58   d  of the received print data packet is smaller than the value of the variable SEQ (S 303 :YES), control returns to step S 302  to receive a next packet.  
         [0137]    When the number in the sequence number field  58   d  of the received print data packet is greater or equal to the value of the variable SEQ (S 303 :NO), the CPU  31  prints the print data contained in the received print data packet  58  on print media using the printing unit  37  (S 305 ).  
         [0138]    In step S 306 , the CPU  31  transmits the ACK packet  59  using the Multicast IP address M 4 . The CPU  31  writes the MAC address in the source address field  58   b  of the received print data packet  58  (i.e., the MAC address of the PC  2 ) into the destination address field  59   a , the MAC address of the printer  3  into the source address field  59   b , and the 2 byte code indicating the ACK packet into the packet type field  59   c . Further, the CPU  31  writes the number contained in the sequence number field  58   d  of the received print data packet  58  into the sequence number field  59   d.    
         [0139]    In step S 308 , the CPU  31  assign the number contained in the sequence number field  58   d  of the received print data packet  58  to the variable SEQ. Then, the CPU  31  determines whether the size of the print data contained in the received print data packet  58  is smaller than 512 bytes (S 308 ).  
         [0140]    When the print data contained in the received print data packet  58  is smaller than 512 bytes (S 308 :NO), since all of the print data have not been received, control returns to step S 302  to repeat steps S 302 - 307 . When the print data contained in the received print data packet  58  is smaller than 512 bytes (S 308 :YES), since all the print data have been received, the multicast print task sleeps.  
         [0141]    As described above, according to the above mentioned embodiment of the present invention, Multicast IP addresses are used for the data transfer process between the PC  2  and the printers  3 , it is unnecessary to install printer drivers into the PC  2 . That is, it is unnecessary to register IP addresses of the printers  3  into the PC  2 .  
         [0142]    It is appreciated that the present invention is effective in a case where a user needs to connect the user&#39;s portable computer to another network (which is different from a network that the user normally uses) and to print out documents on the road.  
         [0143]    Since each packet has the destination address field, a receiving device of the packet can determine whether a received packet is addressed to its own address.  
         [0144]    To use the Multicast IP address M 1  for transmitting the search packet  51  reduces loads to the network (i.e., loads to devices connected to the network) in comparison with to use a broadcast IP address for transmitting the search packet  51 .  
         [0145]    To use the Multicast IP address M 2  for transmitting the print data packet  58  reduces loads to the network (i.e., loads to devices connected to the network) in comparison with to use a broadcast IP address for transmitting the print data packet  58 . Further, to use the Multicast IP address M 2  for transmitting the print data packet  58  reduces loads to the network (i.e., loads to devices connected to the network) in comparison with to use the multicast IP address M 1  for transmitting the print data packet  58  because the packets having the multicast IP address M 2  is only received by the printers joining the print multicast group M 2 /M 4 .  
         [0146]    Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible.  
         [0147]    For example, although MAC addresses are used in each of the packets  51 - 59  to designate the destination addresses or the source addresses, IP addresses may be designated in place of the MAC addresses.  
         [0148]    In the above mentioned embodiment, each of the packets ( 52 ,  55 ,  56 ,  57  and  59 ) which the printer transmits to the PC  2  has the MAC address of the printer, and the PC  2  determines whether the received packet ( 52 ,  55 ,  56 ,  57  and  59 ) is addressed its own address according to the Mac address contained in the received packet ( 52 ,  55 ,  56 ,  57  and  59 ). However, the MAC address of the PC  2  (i.e., the destination address field) can be omitted from the packets ( 52 ,  55 ,  56 ,  57  and  59 ) if the PC  2  determines that each packet which is replied within the predetermined time period after the PC  2  transmits each of the packets ( 51 ,  53 ,  54  and  58 ) is addressed to its own address.  
         [0149]    Although the above mentioned embodiment is described with regard to the data transfer process between the personal computer  2  and the printers  3 ( 3   a - 3   e ), the data transfer process according to the present invention can be applied to various types of data transfer processes between various types of devices (i.e., between a client device and a server device).  
         [0150]    Although in the embodiment the multicast IP addresses used for the data transfer process (i.e., the addresses M 2  and M 4 ) are determined by the printer  3  in step S 206   a  and are transmitted from the printer  3  to the PC  2  in step S 209 , the multicast addresses used for the data transfer process may alternatively be determined by the PC  2  and may be transmitted from the PC  2  to the printer  3 .  
         [0151]    Addresses preset by an administrator or a vendor of the printer  3  may be used as the multicast IP addresses M 2  and M 4 . Although in the embodiment the multicast IP address M 3  is determined by the PC  2  , an address preset by the administrator or the vendor of the printer may be used as the multicast IP address M 3 . Although in the embodiment the multicast IP addresses M 2 -M 4  are transmitted between the PC  2  and the printer  3 , a configuration in which the PC  2  and the printer  3  store in advance the same addresses used as the multicast IP addresses M 2 -M 4  is also possible.  
         [0152]    The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2002-283550, filed on Sep. 27, 2002, which is expressly incorporated herein by reference in its entirety.