JP4413733B2 - Loopback test system, loopback test method, center apparatus, and program - Google Patents

Description

  The present invention relates to a loopback test performed for confirming communication between apparatuses on a communication network.

  As a method for confirming the communication between the devices A and B connected via the communication network, a test frame is transmitted from the device A to the device B, the test frame is returned by the device B, and the test frame is checked by the device A. There is a method to confirm the reception of.

  However, in the related art, when the device A on the user side and the device B on the user side at the other end are connected by a plurality of links via other devices, between the device A and the device B, In order to check end-to-end communication, it is necessary to check the communication by link-by-link by manually entering a command for loopback test. Could not be done.

In the prior art, the loopback test is performed in a state where communication is not being performed, such as when an abnormality occurs, and the loopback test during communication cannot be performed. In addition, there exists patent document 1 as a prior art document regarding a return | turnback test, for example. Further, there are Non-Patent Document 1 and Non-Patent Document 2 as documents that become the background art of the present invention.
JP-A-11-32016 IEEE802.3ah Draft3.3 ITU-T Y.M. 17eeth Draft

  The present invention has been made in view of the above points, and an object of the present invention is to provide a technique for a loopback test that enables efficient end-to-end communication confirmation.

  The above-described problem is a loopback test that includes a first in-home device, a second in-home device, and a center device, and executes a loopback test from the first in-home device to the second in-home device via a communication network. A test frame in which the first in-house device receives a test activation instruction from the center device, the source address is the address of the first in-home device, and the destination address is the address of the second in-home device. The second home device receives the test frame sent from the first home device, uses the source address as the address of the second home device, and sets the destination address as the first home device. A test frame with the address of one home device is sent to the communication network, and the first home device receives the test frame sent from the second home device and receives the test frame. Test results As is transmitted to the center device, the center device can be solved by the folding test system characterized by receiving the test frame as the test result.

  Further, according to the present invention, the first in-house device receives the test activation instruction from the center device, generates a test frame having the source address as the address of the first in-home device and the destination address as the multicast address. The second in-home device that is transmitted to the communication network and is one of the destinations indicated by the multicast address receives the test frame transmitted from the first in-home device, and uses the source address as the address of the second in-home device. And sending a test frame having the destination address as the address of the first home device to the communication network, the first home device receiving the test frame sent from the second home device, The test result may be transmitted to the center apparatus, and the center apparatus may be configured to receive the test frame as the test result.

  Further, according to the present invention, the center device generates and communicates a test frame including the address of the second in-home device with the source address as the address of the center device and the destination address as the address of the first in-home device. The first premises device receives the test frame transmitted from the center device, the transmission source address is the address of the first premises device, and the transmission destination address is the address of the second premises device. A test frame including the address of the center device is transmitted to the communication network, the second in-home device receives the test frame transmitted from the first in-home device, and uses the transmission source address as the address of the second in-home device. The test frame including the address of the first in-home device is transmitted to the center device using the transmission destination address as the address of the center device. Device may also be configured to receive the transmitted test frame from the second home device.

  Further, according to the present invention, the center device generates a test frame having the transmission source address as the center device address and the transmission destination address as the multicast address, and transmits the test frame to the communication network. 1 home device receives the test frame transmitted from the center device, communicates the test frame including the address of the center device with the source address as the address of the first home device and the destination address as the multicast address. The second home device that is sent to the network and is one of the destinations of the multicast address receives the test frame transmitted from the first home device, uses the source address as the address of the second home device, and transmits it. Using the destination address as the address of the center device, including the address of the first home device The test frame was transmitted to the center device, the center device can be configured to receive the transmitted test frame from the second home device.

  Further, according to the present invention, there are provided an in-home device, a center device, a program for causing the in-home device to execute processing, and a program for causing the center device to execute processing for use in the above-described loopback test system.

  According to the present invention, test activation, test result reception, and the like are executed on the center device side, so that even an in-house device such as a DSU or ONU can perform an end-to-end automatic loopback test between in-home devices. It becomes possible to do. Further, in the home device and the center device, since the frame is transmitted if it is not a test frame, the loopback test can be performed even during communication.

  Embodiments of the present invention will be described below with reference to the drawings. In each of the following embodiments, a loopback test in the Ethernet (registered trademark) network will be described as an example. However, the present invention is not limited to the Ethernet (registered trademark) network and can be applied to other networks.

  FIG. 1 shows a configuration of a folding test system 1 in the present embodiment. As shown in FIG. 1, the loopback test system 1 has a user side device 3, a center side device 5, a center side device 7, and a user side device 9, and the center side device 5 and the center side device 7 are Ethernet (registered). The user side device 3 and the center side device 5 and the user side device 9 and the center side device 7 are connected by an access network that is an Ethernet (registered trademark) network.

  The user side device 3 includes a user device 31 which is a computer, for example, and a home device 32 such as a DSU (Digital Service Unit) and an ONU (Optical Network Unit). The user side device 9 on the opposite side has the same configuration, and data communication can be performed between the user device 31 and the user device 91.

  The center side device 5 includes a device for transferring a received frame to another device, and a center device 51 such as an OCU (Office Channel Unit) or an OLT (Optical Line Terminal). The center side device on the opposite side has the same configuration.

  The center device 51 is a device that terminates an interface with the in-home device 32, and the in-home device 32 is a device that terminates an interface with the center device 51. The same applies to the center side device 7 and the user side device 9. The home device 32 and the center device 51 constitute the access system 11, and the home device 92 and the center device 71 constitute the access system 13.

  Each center device activates the test to the in-home device and receives the result, etc., and each in-home device conducts the test and reports the test, returns the test frame, etc. based on the test activation instruction from the center device. I do. It is assumed that the network management system is connected to the center devices 51 and 71 via the network.

  A first embodiment and a second embodiment based on the above configuration will be described below.

(First embodiment)
First, an outline of the operation of the system in the first embodiment will be described with reference to the sequence chart of FIG. This system can support both unicast addresses / multicast addresses as destination addresses, and each will be described below.

  In the following description, it is assumed that the MAC addresses (hereinafter referred to as addresses) of the home device 32, home device 92, center device 51, and center device 71 are A, B, C, and D, respectively. The center device 51 and the center device 71 are displayed as a home device A, a home device B, a center device C, and a center device D, respectively.

[Operation overview: Unicast address]
First, the center apparatus C gives a test activation instruction to the in-home apparatus A using the control frame (step 1). The address B of the in-home device B that is the target of communication confirmation with the in-home device A is included in the test activation instruction.

  Next, the in-home apparatus A generates a test frame having a transmission source address A and a transmission destination address B, and sends it to the network side (step 2). The test frame is a frame that includes identification information for enabling identification from the user frame.

  Upon receipt of the test frame, the in-home apparatus B exchanges the transmission source / destination address and sends it to the network side. That is, a test frame having a transmission source address B and a transmission destination address A is transmitted (step 3).

  Upon receipt of the test frame, the in-home device A transmits the test frame to the center device C (step 4). More specifically, the in-home apparatus A transmits information on the test frame (as a test result) using the control frame. The center apparatus C receives the reception result and confirms that the communication is normal when the in-home apparatus A confirms that the test frame has been received from the in-home apparatus B without timing out (step 5). The center apparatus C may send the received frame to the network management system, and the network management system may determine the result.

[Operation overview: Multicast address]
First, the center apparatus C gives a test activation instruction to the in-home apparatus A using the control frame (step 1). The in-home apparatus A generates a test frame with the transmission source address as A and the transmission destination address as M (predetermined multicast address), and sends it to the network side (step 2). Note that setting the transmission destination as the multicast address is instructed during the test activation.

  Upon receipt of the test frame, the in-home apparatus B, which is one of the destinations of the multicast address, sets its source address to its own B and its destination address to A, that is, sends the address to the network side after changing the address (step 3).

  When receiving the test frame, the in-home apparatus A transmits the test frame as a reception result to the center apparatus C as in the case of unicast (step 4), and the center apparatus C receives the reception result. Then, the network management system manages the in-home device that is to be distributed by the multicast address, and sends the information to the center device C. The center device C detects a time-out and the in-home device A originally receives the information. If the test frame is not received from the home device to be received or the test frame is received from the home device that should not be received, it is determined that the network connection configuration is not normal (step 5). This determination may be performed by a network management system.

[Device configuration]
FIG. 3 shows a device configuration diagram of a home device and a center device in the present embodiment. As illustrated in FIG. 3, the in-home device includes a test execution unit 101 that performs test execution including generation of a test frame based on an instruction from the test control unit 102, and a test control unit 102 that receives a test activation instruction and notifies a reception result. A user interface 103 for connection with a user device, a test frame extracting / inserting unit 104, a control frame extracting / inserting unit 105 for extracting / inserting a control frame exchanged with the center device, and access An access interface 106 for connection to the network is provided.

  The center device also sends a test start instruction, time management, result determination, etc., a test control unit 111, a control frame extraction / insertion unit 112, a user interface 113 for connection to a home device, and a connection to a relay network An access interface 114 and a management system interface 115 which is an interface with the network management system. Both the home device and the center device have a memory for storing various data.

  Each of the in-home device and the center device includes a central processing unit and a memory, and a program for executing the operation described below is loaded from the network or recording medium to the in-home device or the center device. An in-home device and a center device can also be realized. The same applies to the second embodiment.

  Hereinafter, the operation of the system including each device having such a configuration will be described in detail.

[Details of operation]
FIG. 4 is a flowchart showing the operations of the center device and the home device. Hereinafter, the operations of the center device and the in-home device will be described with reference to FIG. In FIG. 4, the process in the test control column is mainly executed in the test control unit in the apparatus configuration, and the process in the test execution column is mainly executed in the test execution unit.

  As shown in FIG. 4, the center device sends a test activation instruction to the in-home device (step 11) and activates a timer (step 12).

  It is checked whether or not the time is up any time (whether or not a predetermined time has elapsed since the timer is started) (step 13). If the time is up without receiving the result, it is determined that the result is NG (step 14). ). When the result is received without time-up (step 15), it is determined whether or not the result is OK (steps 16, 17, and 14). Whether or not the result is OK is determined, for example, based on whether or not a test frame is returned from the destination address of the designated test frame.

  As shown in FIG. 4, in the present embodiment, the center apparatus performs only test control, and does not perform test execution such as transmission of test frames.

  Next, the operation of the home device will be described. The operation of the home device is divided into a case where a test activation instruction is received and a case where a frame is received.

  When the test activation instruction is received, the test activation instruction is received from the center apparatus (step 21), and a test frame is generated and transmitted to another in-home apparatus (step 22). At this time, the type information setting indicating “return required frame (Request)” is performed on the test frame.

  When receiving a frame, when receiving the frame (step 31), it is determined whether or not the frame is from the subscriber side (step 32). If it is from the subscriber side, it is determined whether or not the frame is a test frame (step 33). If it is not a test frame, the frame is transmitted (step 34). Discard (step 35). By making such a determination, a test can be performed even during communication.

  If it is determined in step 32 that the frame is not from the subscriber side, it is determined whether or not the frame is a test frame (step 36). If it is not a test frame, the frame is transmitted (step 37). By making such a determination, a test can be performed even during communication.

  If it is a test frame, it is determined whether or not the frame is addressed to itself (including a multicast address) (step 38). If it is not addressed to itself, the test frame is discarded (step 39). If so, the type of the test frame is identified (step 40). More specifically, it is identified whether the frame is “required return frame (Request)” or “required result notification frame (Reply)”. The type information indicating “required return frame (Request)” or “required result notification frame (Reply)” is set, for example, in the data portion of the MAC frame.

  If the result of the identification is none, the test frame is discarded (step 41). If the frame is a return frame (Request), the type of the required result notification frame (Reply) is set in the test frame in which the above-described address is set, and the frame is returned to the home device that is the transmission source of the test frame (Step 42). . If it is a required result notification frame (Reply), the test frame is transmitted as a reception result to the center apparatus instructed to start the test (step 43).

  FIG. 5 is a flowchart showing a series of operations of each device when a test frame is sent from the home device A to the home device B.

  First, the center apparatus C sends a test start instruction to the in-home apparatus A to start a timer. The in-home apparatus A receives the test activation instruction, and transmits a test frame that is a return frame (Request) to the opposite in-home apparatus B. The in-home apparatus B performs the processing shown in steps 31 to 43 in FIG. 4. In this case, since the test frame is a return frame (Request), the test frame is used as a required result notification frame (Reply). Sent to A. The in-home apparatus A also performs the processing shown in steps 31 to 43 in FIG. 4. In this case, since the test frame is a result notification frame (Reply), the reception result is notified to the center apparatus C. The center apparatus performs processing in steps 13 to 17 in FIG.

  In this embodiment, when performing a test designating a multicast address as a destination, it is determined that the received test frame is a return frame (Request) if the destination of the received test frame is a multicast address without using the type information. However, if the destination is a unicast address, the in-home device may be configured to determine that it is a required result notification frame (Reply).

  According to the present embodiment, test activation and result reception are executed on the center apparatus side, so that an end-to-end loopback test using a relatively small-scale home apparatus such as DSU or ONU can be realized.

(Second Embodiment)
Next, a second embodiment will be described. In the second embodiment, the center device executes a part of the test execution processing that is performed by the in-home device in the first embodiment. An outline of the operation of the system in the second embodiment will be described with reference to the sequence chart of FIG. This system can support both unicast addresses / multicast addresses as destination addresses, and each will be described below.

[Operation overview: Unicast address]
First, the center device C generates a test frame in which the transmission source address is C, the transmission destination address is A, and the address B of the return-target home device is stored in the data portion of the MAC frame. The test frame is transmitted (step 1).

  When the in-home apparatus A receives the test frame, the transmission source address is set to its own A, the transmission destination address is set to B, and C, which is the address of the test frame transmission source center apparatus, is stored in the data portion of the MAC frame. Is sent to the network side (step 2).

  Upon receipt of the test frame, the in-home apparatus B sets its source address as its own B, sets its destination address as C, stores A as the address of the test frame source in-home apparatus in the data portion, and transmits the test frame to the network. (Step 3). Then, the center apparatus C receives the test frame and determines the result of the loopback test (step 4).

[Operation overview: Multicast address]
First, the center apparatus C generates a test frame in which the transmission source address is C, the transmission destination address is M (predetermined multicast address), and all 0s are stored in the data portion of the MAC frame. (Step 1).

  When home device A, one of the test frame destinations, receives the test frame, the source address is A, the destination address is M (multicast address), and the address of the test frame source center device is stored in the data portion. Is sent to the network side (step 2). The home device is configured to determine that the multicast address “M” is continuously used as the transmission destination of the test frame when all 0s are stored in the data portion. This process is based on this determination.

  Upon receipt of the test frame, the premises device B, which is one of the transmission destinations of the test frame transmitted from the premises device A, sets its source address as its own B, its destination address as C, and tests the data portion. A test frame storing A, which is the address of the frame transmission source premises equipment, is sent to the network side (step 3). The in-home device is configured to determine that the address stored in the data portion of the received frame is used as the destination address, except when the data portion is all zeros. Based on. Then, the center apparatus C receives the test frame and determines the result of the return test (step 4).

[Device configuration]
FIG. 7 shows a device configuration diagram of a home device and a center device in the present embodiment.

  As shown in FIG. 7, the in-home device includes a test execution unit 121 that performs test frame folding, a user interface 122, a test frame extraction / insertion unit 123, and an access interface 124.

  The center apparatus also includes a test control unit 131 that performs test activation, time management, and result determination, a test execution unit 132 that performs test execution such as test frame transmission and reception, a test frame extraction / insertion unit 133, and a user interface 134. , An access interface 135, and a management system interface 136 that is an interface with the network management system.

  Hereinafter, the operation of the system having such a configuration will be described in detail.

[Details of operation]
FIG. 8 is a flowchart showing the operations of the center device and the home device. Hereinafter, the operations of the center device and the home device will be described with reference to FIG. In FIG. 8, the process in the test control column is mainly executed in the test control unit in the apparatus configuration, and the process in the test execution column is mainly executed in the test execution unit.

  As shown in FIG. 8, the center apparatus starts a test (step 51) and starts a timer (step 52). The test activation may be performed periodically, for example, or may be activated based on an instruction from the network management system.

  Thereafter, the test frame in which the above-described address is set is sent to the corresponding in-home device (step 53). Then, it is checked whether or not the time is up (step 54). If the time is up without receiving the test frame as a result, it is determined that the result is NG (step 55). If the result is received without time-up (step 56), it is determined whether or not the result is OK (steps 57, 58, and 55). Whether or not the result is OK is determined, for example, based on whether or not a test frame is returned from a specified destination address. The received test frame may be sent to the network management system, and the network management system may determine the result.

  When the center apparatus receives a frame (step 61), it is determined whether or not the frame is a test frame (step 62). If it is not a test frame, the frame is transmitted (step 63). If it is a test frame, it is determined whether or not the frame is addressed to itself (step 64). If it is not addressed to itself, the frame is transmitted (step 65). And the processing of steps 54 to 58 is executed.

  Next, the operation of the home device will be described. When the home device receives the frame (step 71), it is determined whether or not the frame is from the subscriber side (step 72). If it is from the subscriber side, it is determined whether or not the frame is a test frame (step 73). If it is not a test frame, the frame is transmitted (step 74). Discard (step 75).

  If it is determined in step 72 that the frame is not from the subscriber side, it is determined whether or not the frame is a test frame (step 76), and if it is not a test frame, the frame is transmitted (step 77). If it is a test frame, it is determined whether or not the frame is addressed to itself (including a multicast address) (step 78). If it is not addressed to itself, the test frame is discarded (step 79). For example, the address of the test frame is set and turned back (step 80).

  FIG. 9 is a flowchart showing a series of operations of each device when the center device C sends a test frame to the in-home device A side and performs a return test from the in-home device A to the in-home device B.

  First, the center apparatus C issues a test activation instruction, activates a timer, and transmits a test frame. The in-home apparatus A that has received the test frame performs the processing of steps 71 to 80 in FIG. 8. In this case, the test frame is returned with the transmission destination address set to B or a multicast address. The center apparatus C that has received the test frame performs the processing of steps 61 to 65 in FIG. 8. In this case, since the test frame is not addressed to the center apparatus C, the test frame is transmitted to the in-home apparatus B. Sent.

  And the in-home apparatus B which received the test frame performs the process of the part of step 71-step 80 of FIG. In this case, the test frame is folded back to the center apparatus C. The center apparatus C that has received the test frame performs the processing of steps 61 to 65 and steps 54 to 58 in FIG. 8 to determine the result of the folding test.

  In the second embodiment, a part of the processing related to test execution such as test frame generation and transmission is performed by the center device, so that the configuration of the in-home device is further simplified than in the case of the first embodiment. Can be

  The present invention is not limited to the above-described embodiments, and various modifications and applications can be made within the scope of the claims.

It is a lineblock diagram of the return test system in an embodiment of the invention. It is a sequence chart which shows the operation | movement outline | summary of the return | turnback test system in 1st Embodiment. It is an apparatus block diagram of the in-home apparatus and center apparatus in 1st Embodiment. It is a flowchart which shows operation | movement of the in-home apparatus and center apparatus in 1st Embodiment. It is a flowchart which shows a series of operation | movement of each apparatus in 1st Embodiment. It is a sequence chart which shows the operation | movement outline | summary of the return | turnback test system in 2nd Embodiment. It is an apparatus block diagram of the subscriber | terminal apparatus and center apparatus in 2nd Embodiment. It is a flowchart which shows operation | movement of the in-home apparatus and center apparatus in 2nd Embodiment. It is a flowchart which shows a series of operation | movement of each apparatus in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Folding test system 3, 9 User side apparatus 5, 7 Center side apparatus 31, 91 User apparatus 32, 92 In-home apparatus 51, 71 Center apparatus 11, 13 Access system 101, 121, 132 Test execution part 102, 111, 131 test Control unit 103, 113, 122, 134 User interface 104, 123, 133 Test frame extraction / insertion unit 105, 112 Control frame extraction / insertion unit 106, 114, 124, 135 Access interface 115, 136 Management system interface

Claims (4)

First home device, a second home device, the first center device, and a second center device, loopback testing system to perform loopback testing against the first home device to the second home device Because
The first center device and the second center device are connected by a relay network, the first home device is connected to the first center device by the first access network, and the second home device is the second center device. Connected by a second access network,
The first center device generates a test frame including the address of the second in-home device with the source address as the address of the first center device and the destination address as the address of the first in-home device . 1 to the access network,
The first home device, a transmission output to the test frame from the first center device receives via the first access network, the source address and the address of the first home device, the destination address a second A test frame including the address of the first center device is sent to the first access network as the home device address of
The first center device receives the test frame sent from the first in-home device via the first access network, transmits the test frame to the relay network, and the second center device Receiving the test frame sent from the first center device via the relay network, transmitting the test frame to the second access network,
The second home device receives the test frame transmitted from the second center device via the second access network, uses the source address as the address of the second home device, and sets the destination address as the first address . as the address of the center apparatus, and exits send a test frame including the address of the first home device to the second access network,
The second center device receives the test frame transmitted from the second in-home device via the second access network, transmits the test frame, and transmits the test frame to the relay network.
The first center device, a transmission output to the test frame from the second center device receives via the relay network, by the transmission source of the test frame to determine whether a second home device A loopback test system for determining a loopback test result from the first household device to the second household device . A loopback test in which a loopback test system having a first household device, a second household device, a first center device, and a second center device performs a loopback test from the first household device to the second household device. A method,
In the loopback test system, the first center device and the second center device are connected by a relay network, the first home device is connected to the first center device by the first access network, and the second home device Is connected to a second center device by a second access network, and the loopback test method comprises:
The first center device generates a test frame including the address of the second in-home device with the source address as the address of the first center device and the destination address as the address of the first in-home device. Sending to one access network;
The first in-home device receives the test frame transmitted from the first center device via the first access network, uses the source address as the address of the first in-home device, and sets the destination address as the second address. Sending a test frame including the address of the first center device to the first access network as the address of the home device;
The first center device receives the test frame sent from the first in-home device via the first access network, transmits the test frame to the relay network, and the second center device Receiving a test frame sent from the first center apparatus via a relay network, transmitting the test frame to the second access network, and
The second home device receives the test frame transmitted from the second center device via the second access network, uses the source address as the address of the second home device, and sets the destination address as the first address. Sending a test frame including the address of the first in-home device to the second access network as the address of the center device;
The second center device receiving the test frame sent from the second in-home device via the second access network, transmitting the test frame to the relay network, and
The first center device receives the test frame transmitted from the second center device via the relay network, and determines whether or not the transmission source of the test frame is the second home device, Determining a result of a loopback test from the first home device to the second home device;
A folding test method characterized by comprising: The first in-house device, the second in-house device, the center device, and the second center device, and used in a turn-back test system that performs a turn-back test from the first in-home device to the second in-home device. A central device,
In the loopback test system, the center device and the second center device are connected by a relay network, the first home device is connected to the center device by a first access network, and the second home device is a second device. The center device is connected to the center device by a second access network,
Means for generating a test frame including the address of the second in-home device, wherein the source address is the address of the center device and the destination address is the address of the first in-home device, and is sent to the first access network; ,
A test frame sent from the first in-home device that has received the test frame sent from the center device, wherein the source address is the address of the first home device and the destination address is the second home device. Means for receiving a test frame including the address of the center device as an address via the first access network, transmitting the test frame to the relay network, and
A test frame transmitted from the second in-house device that has received the test frame transmitted to the relay network and transmitted through the second center device, and the transmission source address is the address of the second in-home device, and the transmission destination A test frame including the address of the first in-home device with the address as the address of the center device is received via the relay network, and whether or not the transmission source of the test frame is the second in-home device A center device comprising: means for determining a result of a loopback test from the first in-home device to the second in-home device by determining. The first in-house device, the second in-house device, the center device, and the second center device, and used in a turn-back test system that performs a turn-back test from the first in-home device to the second in-home device. A program for causing a center device to execute processing,
In the loopback test system, the center device and the second center device are connected by a relay network, the first home device is connected to the center device by a first access network, and the second home device is a second device. It is connected to a center device by a second access network, and the program
Means for generating a test frame including the address of the second in-home device, having the source address as the address of the center device and the destination address as the address of the first in-home device, and sending it to the first access network;
A test frame sent from the first in-home device that has received the test frame sent from the center device, wherein the source address is the address of the first home device and the destination address is the second home device. Means for receiving a test frame including the address of the center device as an address via the first access network, transmitting the test frame to the relay network, and
A test frame transmitted from the second in-house device that has received the test frame transmitted to the relay network and transmitted through the second center device, and the transmission source address is the address of the second in-home device, and the transmission destination A test frame including the address of the first in-home device with the address as the address of the center device is received via the relay network, and whether or not the transmission source of the test frame is the second in-home device Means for determining a result of a return test from the first in-home device to the second in-home device by determining,
A program characterized by functioning as

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