Abstract:
A data transfer system allowing transmission of control information independently of communication protocols is disclosed. A data transmission equipment working in a predetermined communication protocol receives a transmission signal including control information from upstream. The control information is forwarded to a transmitting section without controlling the control information according to the predetermined communication protocol. The transmitting section transmits a transmission signal including the control information to downstream.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to techniques of transferring control information from a control terminal to a target data transmission equipment through a data transmission network.  
           [0003]    2. Description of the Related Art  
           [0004]    With the recent increase in data transmission capacity, SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy) has been employed as a basic transmission scheme for fiber-optic communication systems.  
           [0005]    Taking the terminology of SDH, D1-D3 bytes are defined in Regenerator Section Overhead (RSOH) and D4-D12 bytes are defined in Multiplex Section Overhead (MSOH). These provide data communication channels (DCCs) to transfer control packets (if necessary, see ITU-T G.707 (March, 2000; 9 Overhead bytes description) and G.783 (April, 1997; Appendix VI Data Communication Channel (DCC)).  
           [0006]    In order to transfer a control packet from the control terminal to target optical transmission equipment, a routing function is needed. As well known, the routing function can be realized by different protocols, for example, the TCP/IP protocol stack and the OSI protocol stack. In the case where the control terminal and optical transmission equipments all work based on the same routing protocol, it is possible for the control terminal to control each optical transmission equipment. However, in the case where network elements working in a different routing protocol exist between the control terminal and a target optical transmission equipment, the control packet cannot reach the target optical transmission equipment as described hereinafter.  
           [0007]    As shown in FIG. 1, it is assumed that a control terminal  1  and optical transmission equipments  2  and  3  work in the same communication (routable) protocol A and a control terminal  4  and optical transmission equipments  5  and  6  work in a different communication (routable) protocol B, wherein the optical transmission equipments  5  and  6  are connected through the optical transmission equipments  2  and  3 . In this network system, when the control terminal  4  sends a control packet (B) to the target optical transmission equipment  6  through the optical transmission equipment  5 , the optical transmission equipment  2  receives the control packet (B) conformable to the different communication protocol B. Accordingly, the optical transmission equipment  2  cannot provide routing processing to the control packet (B).  
           [0008]    Japanese Patent Application Unexamined Publication No. P2002-171274A discloses a method for transferring data between networks working in different protocols. For example, data of a first data frame conformable to a first communication (routable) protocol is combined with a header for a second communication (routable) protocol to produce a second data frame, allowing the second data frame to be transferred in the second network.  
           [0009]    However, such a conversion between the first and second data frames is effective only in a combination of the first and second protocols, not working in a third protocol different from the first and second protocols.  
         SUMMARY OF THE INVENTION  
         [0010]    An object of the present invention is to provide data transfer method and system allowing transmission of control information through a network including transmission equipments working in different communication protocols, independently of communication protocols.  
           [0011]    According to the present invention, a data transmission equipment working in a predetermined communication protocol includes: a receiving section for receiving a transmission signal including control information from upstream; a transmitting section for transmitting a transmission signal including control information to downstream; and a forwarding section for forwarding control information included in a received transmission signal to the transmitting section without controlling the control information according to the predetermined communication protocol.  
           [0012]    The forwarding section may include: a data extractor for extracting the control information from the received transmission signal; and a data inserter for inserting the extracted control information into a predetermined one of a first location and a second location of the transmission signal to be transmitted.  
           [0013]    In an embodiment, the first location is data communication channel (DCC) bytes of the transmission signal and the second location is DCC transmit bytes that are previously determined in the transmission signal.  
           [0014]    The data transmission equipment may be set to one of the following configurations:  
           [0015]    1) the data extractor extracts the control information from the first location of the received transmission signal, and the data inserter inserts the extracted control information into the second location;  
           [0016]    2) the data extractor extracts the control information from the second location of the received transmission signal, and the data inserter inserts the extracted control information into the second location; and  
           [0017]    3) the data extractor extracts the control information from the second location of the received transmission signal, and the data inserter inserts the extracted control information into the first location.  
           [0018]    According to another aspect of the present invention, in a data transfer system for transferring control information from a control terminal to a target through a data transmission network including at least one data transmission equipment working in a predetermined communication protocol, a data transfer method at each of said at least one data transmission equipment, includes: a) receiving a transmission signal including control information at a receiving section from upstream; b) forwarding control information included in a received transmission signal to a transmitting section without controlling the control information according to the predetermined communication protocol; and c) transmitting a transmission signal including the control information from the transmitting section to downstream.  
           [0019]    As described above, according to the present invention, the data transmission equipment can transfer the control information without control by the predetermined communication protocol. Accordingly, the control information is transferred from the control terminal to a targeted data transmission equipment through the data transmission network. Since the data transmission equipment do not provide control by the predetermined communication protocol to the control information, control information for any communication protocol can be transferred.  
           [0020]    Further, in the case of a network composed of a plurality of data transmission equipments working in the same communication protocol, data transmission equipments according to the present invention can transfer control information without routing processing, resulting in the reduced number of hops from the control terminal to a targeted equipment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a block diagram showing a communication network employing a conventional data transfer system;  
         [0022]    [0022]FIG. 2 is a block diagram showing a Communication network employing a data transfer system according to a first embodiment of the present invention;  
         [0023]    [0023]FIG. 3 is a diagram showing allocation of Section Overhead bytes in a SDH frame so as to explain data communication bytes D 1 -D 12 ;  
         [0024]    [0024]FIG. 4 is a diagram showing allocation of Section Overhead bytes in a SDH frame so as to explain data communication transmit bytes;  
         [0025]    [0025]FIG. 5 is a block diagram showing an overhead processing section of optical transmission equipment according to the first embodiment of the present invention;  
         [0026]    [0026]FIG. 6 is a diagram showing an example of an optical transmission network employing the data transfer system according to the first embodiment of the present invention;  
         [0027]    [0027]FIG. 7 is a diagram showing an example of cross-connect control information for each optical transmission equipment according to the first embodiment;  
         [0028]    [0028]FIG. 8 is a diagram showing an example of data communication byte select information for each optical transmission equipment according to the first embodiment;  
         [0029]    [0029]FIG. 9A is a flowchart showing an operation of optical transmission equipment OTE 2  according to the first embodiment;  
         [0030]    [0030]FIG. 9B is a block diagram showing a schematic structure of the optical transmission equipment OTE 2  for explaining its cross-connect operation;  
         [0031]    [0031]FIG. 10A is a flowchart showing an operation of optical transmission equipment OTE 3  according to the first embodiment;  
         [0032]    [0032]FIG. 10B is a block diagram showing a schematic structure of the optical transmission equipment OTE 3  for explaining its cross-connect operation;  
         [0033]    [0033]FIG. 11A is a flowchart showing an operation of optical transmission equipment OTE 4  according to the first embodiment;  
         [0034]    [0034]FIG. 11B is a block diagram showing a schematic structure of the optical transmission equipment OTE 4  for explaining its cross-connect operation; and  
         [0035]    [0035]FIG. 12 is a block diagram showing a communication network employing a data transfer system according to a second embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    As shown in FIG. 2, for the sake of simplicity, it is assumed that a network is composed of a control terminal  11  and optical transmission equipments  12  and  13  working in the same communication (routable) protocol A, and a control terminal  14  and optical transmission equipments  15  and  16  working in a different communication (routable) protocol B. Accordingly, the optical transmission equipments  12  and  13  are allowed to provide routing processing to control packet (A) based on the communication protocol A. The optical transmission equipments  15  and  16  are allowed to provide routing processing to control packet (B) based on the communication protocol B.  
         [0037]    In this example, the optical transmission equipment  15  is connected to the optical transmission equipment  12  through an optical line a, the optical transmission equipments  15  and  13  are connected through an optical line b, and the optical transmission equipment  13  is connected to the optical transmission equipment  16  through an optical line c.  
         [0038]    According to the present invention, the optical transmission equipments  12  and  13  can provide routing processing to a control packet (B) without protocol processing. The details will be described later. Therefore, when the control terminal  14  sends a control packet (B) to the target optical transmission equipment  16  through the optical transmission equipment  15 , the optical transmission equipment  12  receives the control packet (B) from the optical transmission equipment  15  and transmits it to the optical transmission equipment  13  through the optical line b. When having received the control packet (B) from the optical transmission equipment  12 , the optical transmission equipment  13  transmits it to the optical transmission equipments  16  through the optical line c.  
         [0039]    Taking the SDH system as an example, a data transfer system according to a first embodiment of the present invention will be described with reference to figures.  
       1. DCC Transmit Bytes  
       [0040]    As shown in FIG. 3, D1-D3 bytes of RSOH and D4-D12 of MSOH are defined as Data Communication Channels (DCCs) in the section overhead of a SDH frame. Hereinafter, D1-D3 bytes or D4-D12 bytes are referred to as DCC bytes.  
         [0041]    According to the present invention, not-yet-defined or reserved bytes used for control information transmission are referred to as DCC transmit bytes.  
         [0042]    As shown in FIG. 4, Z 2  bytes of columns  5 - 2 ,  5 - 3  and  5 - 4  in the 9th line are used as DCC transmit bytes corresponding to DCC (D1-D3) bytes. Z 2  bytes of columns  6 - 2 ,  6 - 3  and  6 - 4  in the 9th line, NU bytes of columns  8 - 2 ,  8 - 3  and  8 - 4  in the 9th line, and NO bytes of columns  9 - 2 ,  9 - 3  and  9 - 4  in the 9th line are used as DCC transmit bytes corresponding to DC:C (D4-D12) bytes.  
         [0043]    The DCC transmit bytes can be assigned to any combination of bytes that are not used for other functions. Therefore, the DCC transmit bytes are not restricted to the SDH frame as shown in FIG. 4. Similarly, DCC transmit bytes may be applied to the section overhead of another level SDH frame.  
       2. Optical Transmission Equipment  
       [0044]    Referring to FIG. 5, optical transmission equipment according to the first embodiment of the present invention, which may be the optical transmission equipment  12  or  13  shown in FIG. 2, is connected to two optical input lines L IN1  and L IN2  and two optical output lines L OUT1  and L OUT2 .  
         [0045]    In FIG. 5, for the sake of simplicity, the overhead processing section of the optical transmission equipment is mainly shown and the payload forwarding section is omitted.  
         [0046]    The optical transmission equipment is provided with optical interface sections  101  and  201  each connected to the optical input lines L IN1  and L IN2  and optical interface sections  109  and  209  each connected to the optical output lines L OUT1  and L OUT2 .  
         [0047]    The optical interface section  101  receives an optical transmission signal through the optical input line L IN1  and outputs a received signal to an overhead receiver (OH RCV)  102  The overhead receiver  102  extracts RSOH and MSOH front the received signal and outputs the RSOH and MSOH to both a DCC transmit byte extractor  103  and a DCC byte extractor  104 . The DCC transmit byte extractor  103  extracts DCC transmit data from the DCC transmit bytes of the RSOH and MSOH to output it to an input port P IN1  of a cross connect  303 . The DCC byte extractor  104  extracts DCC data from the DCC bytes of the RSOH and MSOH to output it to an input port P IN2  of the cross connect  303  and a DCC byte processor  301 .  
         [0048]    Similarly, the optical interface section  201  receives an optical transmission signal through the optical input line L IN2  and outputs a received signal to an overhead receiver (OH RCV)  202 . The overhead receiver  202  extracts RSOH and MSOH from the received signal and outputs the RSOH and MSOH to both a DCC transmit byte extractor  203  and a DCC byte extractor  204 . The DCC transmit byte extractor  203  extracts DCC transmit data from the DCC transmit bytes of the RSOH and MSOH to output it to an input port P IN3  of the cross connect  303 . The DCC byte extractor  204  extracts DCC data from the DCC bytes of the RSOH and MSOH to output it to an input port P IN4  of the cross connect  303  and the DCC byte processor  301 .  
         [0049]    The DCC byte processor  301  produces a control packet from the DCC data received from the DCC byte extractor  104  or the DCC byte extractor  204  and provides routing processing to the control packet according to the communication protocol. In the case of TCP/IP protocol, the routing processing is performed by looking at IP address of the control packet. DCC data for the routing-processed control packet is output to one input of a corresponding one of selectors  105  and  205 .  
         [0050]    The cross connect  303  connects the input ports P IN1 -P IN4  to appropriate ones of output ports P OUT1 -P OUT4  depending on control information CTRL received from a processor  302 . An example of the control information CTRL will be described later (see FIG. 7). The output port P OUT1  is connected to a DCC transmit byte inserter  106 , the output port P OUT2  is connected to the other input of the selector  105 , the output port P OUT3  is connected to a DCC transmit byte inserter  206 , and the output port P OUT4  is connected to the other input of the selector  205 .  
         [0051]    The respective selectors  105  and  205  are independently controlled by selection signals SEL 1  and SEL 2  received from the processor  302 . An example of the selection signals SEL 1  and SEL 2  will be described later (see FIG. 8). The selector  105  selects One of DCC data received from the output port P OUT2  and DCC data received from the DCC byte processor  301 , and outputs a selected one to the DCC byte inserter  107 . Similarly, the selector  205  selects one of DCC data received from the output port P OUT4  and DCC data received from the DCC byte processor  301 , and outputs a selected one to the DCC byte inserter  207 .  
         [0052]    The DCC transmit byte inserter  106  receives DCC transmit data from the output port P OUT1  of the cross connect  303  and inserts it into the DCC transmit bytes of RSOH or MSOH to output to an overhead generator  105 . The DCC byte inserter  107  receives DCC data from the selector  105  and inserts it into the DCC bytes of RSOH or MSOH to output to the overhead generator  108 .  
         [0053]    Similarly, the DCC transmit byte inserter  206  receives DCC transmit data from the output port P OUT3  of the cross connect  303  and inserts it into the DCC transmit bytes of RSOH or MSOH to output to an overhead generator  208 . The DCC byte inserter  207  receives DCC data from the selector  205  and inserts it into the DCC bytes of RSOH or MSOH to output to the overhead generator  208 .  
         [0054]    The overhead generator  108  generates a section overhead to be transmitted from the RSOH and MSOH received from the DCC transmit byte inserter  106  and the DCC byte inserter  107 . The section overhead to be transmitted and the payload (not shown) are transmitted through the optical interface  109  as an optical transmission signal to the optical output line L OUT1 .  
         [0055]    Similarly, the overhead generator  208  generates a section overhead to be transmitted from the RSOH and MSOH received from the DCC transmit byte inserter  206  and the DCC byte inserter  207 . The section overhead to be transmitted and the payload (not shown) are transmitted through the optical interface  209  as an optical transmission signal to the optical output line L OUT2 .  
         [0056]    As described above, the processor  302  may be a program-controlled processor such as a CPU (Central Processing Unit) that controls interconnection of the cross connect  303  and selection of the selectors  105  and  205  by running control programs with user&#39;s setting data, which are previously stored in a memory  304 . The control programs include one of operation control programs shown in FIGS. 9A, 10A and  11 A. The user&#39;s setting data determines the cross connect control information CTRL and the selection information SEL 1  and SEL 2 , as shown in FIGS. 7 and 8.  
       3. Data Transfer Operation  
       [0057]    An operation of the above-described optical transmission equipment of FIG. 5 will be described in detail, taking as an example an optical transmission network as shown in FIG. 6.  
         [0058]    Referring to FIG. 6, it is assumed that the optical transmission network is composed of optical transmission equipments OTE 1 -OTE 5 , which are connected in series such that the optical transmission equipments OTE 1  and OTE 2  are connected by an optical line L 1 , the optical transmission equipments OTE 2  and OTE 3  by an optical line L 2 , the optical transmission equipments OTE 3  and OTE 4  by an optical line L 3 , and the optical transmission equipments OTE 4  and OTE 5  by an optical line L 4 .  
         [0059]    The optical transmission equipments OTE 2 -OTE 4  work in a communication protocol A (e.g. TCP/IP) and the optical transmission equipments OTE 1  and OTE 5  work in a different communication protocol B (e.g. OSI). Accordingly, the optical transmission equipment OTE 2  is connected to the optical transmission equipment OTE 1  working in the different communication protocol B and to the optical transmission equipment OTE 3  working in the same communication protocol A. The optical transmission equipment OTE 3  is connected to the optical transmission equipment OTE 2  working in the same communication protocol A and also to the optical transmission equipment OTE 4  working in the same communication protocol A. The optical transmission equipment OTE 4  is connected to the optical transmission equipment OTE 3  working in the same communication protocol A and to the optical transmission equipment OTE 5  working in the different communication protocol B. In this example, the optical transmission equipments OTE 2 -OTE 4  are provided according to the first embodiment as shown in FIG. 5.  
         [0060]    In such a network, when control information (B) is transferred from the optical transmission equipment OTE 1  to the optical transmission equipment OTE 5 , the operation of each of the optical transmission equipments OTE 2 -OTE 4  will be described hereinafter.  
         [0061]    3.1) Cross Connect Control Information CTRL  
         [0062]    It is assumed that the cross connect control information for each optical transmission equipment has been set as shown in FIG. 7.  
         [0063]    More specifically, in the optical transmission equipment OTE 2 , the processor  302  generates the cross connect control information CTRL based on the user&#39;s setting data to output it to the cross connect  303 , which is set thereby to an interconnection state such that the input port P IN2  is connected to the output port P OUT3 .  
         [0064]    Similarly, in the optical transmission equipment OTE 3 , the cross connect  303  is set to an interconnection state such that the input port P IN1  is connected to the output port P OUT3 . In the optical transmission equipment OTE 4 , the cross connect  303  is set to an interconnection state such that the input port P IN1  is connected to the output port P OUT4 .  
         [0065]    3.2) Selection Information SEL 1  and SEL 2   
         [0066]    As shown in FIG. 8, in the optical transmission equipment OTE 2 , the processor  302  generates the selection information SEL 1  and SEL 2  based on the user&#39;s setting data to output them to the respective selectors  105  and  205 , causing the selectors  105  and  205  to select DCC data inputted from the DCC byte processor  301 . In the optical transmission equipment OTE 3 , the selectors  105  and  205  also select DCC data inputted from the DCC byte processor  301 .  
         [0067]    However, in the optical transmission equipment OTE 4 , the processor  302  outputs the selection information SEL 1  and SEL 2  to the respective selectors  105  and  205 , causing the selector  105  to select DCC data inputted from the DCC byte processor  301  and the selector  205  to select DCC transmit data inputted from the output port P OUT4  of the cross connect  303 .  
         [0068]    3.3) Transmission Operation at OTE 2   
         [0069]    Referring to FIG. 9A, when having received an optical transmission signal through the optical input line L IN1  (here, L 1 ) (step S 1 ), the DCC byte extractor  104  extracts DCC bytes from the received signal (step S 2 ) and Outputs the DCC bytes to the DCC byte processor  301  and the cross connect  303  (step S 3 ).  
         [0070]    Since the cross connect  303  connects the input port P IN2  to the output port P OUT3  as described above (see FIG. 9B), the DCC bytes are forwarded from the input port P IN2  to the output port P OUT3 , from which the DCC bytes are outputted to the DCC transmit byte inserter  206  (step S 4 ). Accordingly the DCC transmit bytes are transmitted to the optical output line L OUT2  (here, L 2 ) through the OH generator  208  and the optical interface section  209  (step S 5 ).  
         [0071]    On the other hand, since the selector  205  selects DCC data from the DCC byte processor  301 , DCC bytes are also transmitted to the optical output line L OUT2  (here, L 2 ) through the selector  205 , the DCC byte inserter  207 , the OH generator  208  and the optical interface section  209 .  
         [0072]    3.4) Transmission Operation at OTE 3   
         [0073]    Referring to FIG. 10A, when having received an optical transmission signal from the OTE 2  through the optical input line L IN1  (here, L 2 ) (step S 11 ), the DCC transmit byte extractor  103  extracts DCC transmit bytes from the received signal (step S 12 ) and outputs the DCC transmit bytes to the cross connect  303  (step  313 ). Further, the DCC byte extractor  104  extracts DCC bytes from the received signal and outputs the DCC bytes to the DCC byte processor  301  and the cross connect  303 .  
         [0074]    Since the cross connect  303  connects the input port P IN1  to the output port P OUT3  as described above (see FIG. 10B), the DCC transmit bytes are forwarded from the input port P IN1  to the output port P OUT3 , from which the DCC transmit bytes are outputted to the DCC transmit byte inserter  206  (step S 14 ). Accordingly the DCC transmit bytes are transmitted to the optical output line L OUT2  (here, L 3 ) through the OH generator  208  and the optical interface section  209  (step S 15 ).  
         [0075]    On the other hand, since the selector  205  selects DCC data from the DCC byte processor  301 , the routing-processed DCC bytes outputted from the DCC byte processor  301  to the selector  205  are also transmitted to the optical output line L OUT2  (here, L 3 ) through the selector  205 , the DCC byte inserter  207 , the OH generator  208  and the optical interface section  209 .  
         [0076]    3.5) Transmission Operation at OTE 4   
         [0077]    Referring to FIG. 11A, when having received an optical transmission signal from the OTE 3  through the optical input line L IN1  (here, L 3 ) (step S 21 ), the DCC transmit byte extractor  103  extracts DCC transmit bytes from the received signal (step S 22 ) and outputs the DCC transmit bytes to the cross connect  303  (step S 23 ). Further, the DCC byte extractor  104  extracts DCC bytes from the received signal and outputs the DCC bytes to the DCC byte processor  301  and the cross connect  303 .  
         [0078]    Since the cross connect  303  connects the input port P IN1  to the output port P OUT4  as described above (see FIG. 11B), the DCC transmit bytes are forwarded from the input port P IN1  to the output port P OUT4 , from which the DCC transmit bytes are outputted to the DCC byte inserter  207  (step S 24 ).  
         [0079]    Since the selector  205  selects DCC data from the cross connect  303  as shown in FIG. 8 (step S 25 ), the DCC transmit bytes appearing on the output port P OUT4  are transmitted as DCC bytes to the optical output line L OUT2  (here, L 4 ) through the selector  205 , the DCC byte inserter  207 , the OH generator  208  and the optical interface section  209  (step S 26 ).  
         [0080]    As described above, according to the first embodiment of the present invention, the optical transmission equipments OTE 2 -OTE 4  can transfer the control packet (B) without control by the communication protocol A. Accordingly, the control packet is transferred from the optical transmission equipment OTE 1  to the optical transmission equipment OTE 5  through the optical transmission equipments OTE 2 -OTE 4 . Since the optical transmission equipments OTE 2 -OTE 4  do not provide control by the communication protocol A to the control packet (B), a control packet for any communication protocol can be transferred.  
         [0081]    The optical transmission network as shown in FIG. 6 is just an example. The present invention can be applied to any network composed of a plurality of optical transmission equipments like the optical transmission equipment OTE 3  provided between the optical transmission equipments OTE 2  and OTE 4 .  
       4. Second Embodiment  
       [0082]    The present invention can be also applied to any network composed of a plurality of optical transmission equipments working in the same communication protocol.  
         [0083]    As shown in FIG. 12, for the sake of simplicity, it is assumed that a network is composed of a control terminal  21  and optical transmission equipments  22 - 25  working in the same communication protocol C. In such a network, the control terminal  21  can control the optical transmission equipments  22 - 25  by sending a control packet to each of the optical transmission equipments  22 - 25 .  
         [0084]    More specifically, when having received the control packet from the control terminal  21 , at each optical transmission equipment, a DCC byte processor provides routing processing to the control packet according to the communication protocol C. Accordingly, if all the optical transmission equipments  22 - 25  are conventionally configured and the control terminal  21  sends a control packet targeted for the optical transmission equipment  25 , then the number of hops the control packet needs to reach the targeted equipment is 3 in this example.  
         [0085]    In contrast, if the present invention is applied to the optical transmission equipments  23  and  24  as shown in FIG. 5, then the control packet can be transferred to the next hop without routing processing based on the communication protocol C at each of the optical transmission equipments  23  and  24 . More specifically, the respective optical transmission equipments  23  and  24  are configured like the optical transmission equipments OTE 2  and OTE 4  as shown in FIG. 6. Accordingly, when the control terminal  21  sends a control packet targeted for the optical transmission equipment  25 , the number of hops the control packet needs to reach the targeted equipment is reduced to 1 in this example.  
         [0086]    In this manner, in a network composed of a plurality of optical transmission equipments working in the same communication protocol, optical transmission equipments according to the present invention can transfer a control packet without routing processing, resulting in the reduced number of hops from the control terminal to a targeted equipment.