JP2021153224A - Network test device and network test method - Google Patents

Abstract

To provide a network test method for expanding a transmission band and generating a stream.SOLUTION: A network test method includes ST1 of generating 100 Gbit band streams individually, ST2 of holding them individually, ST3 of selectively switching and controlling a signal relay processing unit for first reading the streams, ST4 of reading a 100 Gbit band stream in a 400 Gbit band, ST5 of monitoring the holding state of the stream in the 100 Gbit band, and selectively switching and controlling a signal relay processing unit which next reads out a stream at an end timing of a frame from a signal relay processing unit which is currently selectively switched, ST6 of reading a 100 Gbit band stream in a 400 Gbit band, and ST7 of performing alignment so that the frame is not interrupted at a halfway position in the stream during switching control, and selecting and outputting the stream of the 400 Gbit band by a logical sum of effective streams from each signal relay processing unit that is selectively switched and controlled in order.SELECTED DRAWING: Figure 3

Description

The present invention relates to a network test device and a network test method for performing various tests using a network device such as a router, a switching hub, or a transmission device or a network line as a device under test (DUT).

For example, as a device for performing various tests using a network device such as a router, a switching hub, or a transmission device or a network line as an object to be measured, for example, a network test device disclosed in Patent Document 1 or Patent Document 2 below is known.

In the network test device, a test signal generated in accordance with the communication standard of the object to be measured is input to the object to be measured, and the signal output from the object to be measured is analyzed in accordance with the input of the test signal to perform various tests. It is carried out.

Japanese Unexamined Patent Publication No. 2015-195468 Japanese Unexamined Patent Publication No. 2015-185861

By the way, in recent years, data communication traffic has been increasing along with the speeding up of networks due to the spread of next-generation 5G mobile communication and cloud communication services, and 400 Gigabit Ethernet (registered trademark) developed by the IEEE802.3bs task force is a company. It is expected as the next-generation technology for networks. For this reason, it has been desired to extend the transmission band of the stream that can be generated in the network test apparatus in order to support high-speed and large-capacity communication.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a network test apparatus and a network test method capable of generating a stream by expanding a transmission band.

In order to achieve the above object, the network test apparatus according to claim 1 of the present invention inputs a data frame of a test signal generated corresponding to the communication standard of the object to be measured W into the object to be measured. In the network test apparatus 1 that measures various tests based on the data frame received from the object to be measured in accordance with the input of the data frame of the test signal.
A plurality of stream generators 12 that generate streams in the first bit band,
A plurality of signal holding units 13 for holding a stream input from the corresponding stream generation unit among the plurality of stream generation units, and a plurality of signal holding units 13.
A plurality of signal relay processing units 14 for reading a stream held in the corresponding signal holding unit among the plurality of signal holding units in a second bit band larger than the first bit band.
The stream holding state of each of the plurality of signal holding units is monitored, and switching control is performed so as to select one signal relay processing unit from the signal relay processing units corresponding to the signal holding units that maintain the stream holding state. Signal monitoring unit 15 and
A signal selection unit 16 that selects an effective stream read by the plurality of signal relay processing units in accordance with the switching control of the signal monitoring unit and sets the stream in the second bit band is provided.
The signal relay processing unit notifies the signal monitoring unit and the signal relay processing unit to be the next switching control target of the end of the frame in the stream read in the second bit band from the corresponding signal holding unit, and the signal monitoring. Alignment is performed so that the frame is not interrupted in the stream during switching control by the unit.
The signal monitoring unit is characterized in that it switches and controls one signal relay processing unit from the signal relay processing units corresponding to the signal holding unit that maintains the holding state of the stream at the timing when the notification of the end of the frame is received. And.

In the network test method according to claim 2 of the present invention, a data frame of a test signal generated corresponding to the communication standard of the object W to be measured is input to the object to be measured, and the data frame of the test signal is used. In a network test method in which measurements of various tests are performed based on a data frame received from the object to be measured in response to input.
A step of individually generating a stream of the first bit band by a plurality of stream generation units 12 and
A step of individually holding the streams individually generated by the plurality of stream generation units in the plurality of signal holding units 13, and a step of individually holding the streams.
A step of reading a stream individually held by the plurality of signal holding units in a second bit band larger than the first bit band by the corresponding signal relay processing unit of the plurality of signal relay processing units 14.
A step of monitoring the holding state of the stream individually held by the plurality of signal holding units by the signal monitoring unit 15, and a step of monitoring each of them.
The signal relay processing for which the signal relay processing unit is subject to the next switching control with the signal monitoring unit for the end of a frame in the stream read in the second bit band from the corresponding signal holding unit among the plurality of signal holding units. Steps to notify the department and
A step of switching and controlling the signal relay processing unit corresponding to the signal holding unit that holds the stream holding state at the timing when the signal monitoring unit receives the notification of the end of the frame to one signal relay processing unit.
The step of aligning the frame so that the frame is not interrupted in the stream during the switching control, and
It is characterized by including a step of selecting a valid stream read by the plurality of signal relay processing units in accordance with the switching control of the signal monitoring unit and converting it into a stream of the second bit band.

According to the present invention, it is possible to generate a stream by expanding the transmission band, and it is possible to easily and inexpensively cope with an increase in the transmission rate in the future.

It is a block block diagram of the network test apparatus which concerns on this invention. It is a block block diagram of the stream generation circuit in FIG. It is a flowchart which shows the procedure of the transmission band extension method by the network test apparatus which concerns on this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings.

As shown in FIG. 1, the network test apparatus 1 of the present embodiment is roughly configured to include an operation unit 2, a signal generation unit 3, an input / output unit 4, a signal measurement unit 5, a control unit 6, and a display unit 7. NS. In the network test device 1, for example, a network device such as a router, a switching hub, or a transmission device or a network line (for example, 100G, 400G Ethernet (registered trademark), etc.) is set as an object to be measured (DUT: Device Under Test) W, and the object to be measured is to be measured. A test signal generated in accordance with the communication standard of W is input to the object W to be measured, and various tests are performed based on the signal from the object W to be measured accompanying the input of the test signal.

The operation unit 2 includes, for example, an operation knob, various keys, switches, and buttons provided in the main body of the device, an input device such as a keyboard and a mouse equipped with a numeric keypad and various setting keys, and a touch panel provided on the surface of the display unit 7. It consists of an input device. The operation unit 2 sets measurement conditions such as start and stop of various measurements of the object W to be measured, measurement intervals, and a code format (NRZ (Non Return to Zero) / PAM) of a data frame transmitted to the object W to be measured. (Pulse Amplitude Modulation)) selection setting, parameters for generating a data frame, and other operations related to various measurements of the object W to be measured are operated by the user.

The signal generation unit 3 generates a data frame of a plurality of lanes as a test signal corresponding to the communication standard of the object to be measured W, and transmits the generated test signal of the data frame of the plurality of lanes to the object to be measured via the input / output unit 4. Send to W. For example, a clock frequency of 330 MHz × 160 bits = 52.8 Gbps is used as a data frame of one lane, and a test signal of a data frame of eight lanes parallel is generated.

The signal generation unit 3 includes a stream generation circuit 11 that generates a stream that is the source of the test signal. In the present embodiment, the stream generation circuit 11 bundles a plurality of 100 Gigabit Ethernet (registered trademark) streams (hereinafter, abbreviated as 100 Gbit band streams) as the first bit band in the first bit band. An example will be described in which the transmission band is extended to a 400 Gigabit Ethernet (registered trademark) stream (hereinafter, abbreviated as a 400 Gbit band stream) as a larger second bit band.

As shown in FIG. 2, the stream generation circuit 11 is composed of a stream generation unit 12, a signal holding unit 13, a signal relay processing unit 14, a signal monitoring unit 15, a signal selection unit 16, and a signal output unit 17. 12, a plurality of signal holding units 13 and a plurality of signal relay processing units 14 (four in the example of FIG. 2) are provided.

Each stream generation unit 12 (12a, 12b, 12c, 12d) generates a stream having a 100 Gbit band. Specifically, each stream generation unit 12a, 12b, 12c, 12d generates a stream of 100 Gbit band (operating clock frequency 200 MHz × 512 bits) in 512 bit units with an operating clock frequency of 200 MHz, and one frame consists of 16000 bytes. ..

The frame is a multiplexing of a plurality of frames based on the transmission interval represented by the Length of the frame and the GAP length between the frames. The basic configuration of the frame is "Preamble (8byte)" which is a transmission text (preamble), "MAC DA (6byte)" which is a destination address, "MAC SA (6byte)" which is a source address, and "Type" which indicates a type. (2byte) ”,“ Data (length restrictions vary depending on the header configuration. In this embodiment, 48 to 15988 bytes: the minimum frame length that can be generated is 60 bytes, and the maximum frame length is 16000 bytes. The total number of bytes from MAC DA to FCS = frame length 60 to 16000 bytes) ”and“ FCS (4 bytes) ”for error detection.

The streams of the 100 Gbit band generated by the stream generation units 12a, 12b, 12c, and 12d are input to the corresponding signal holding units 13 (13a, 13b, 13c, 13d) in the subsequent stage.

Each signal holding unit 13 (13a, 13b, 13c, 13d) is composed of a FIFO type buffer, and is generated and input by the corresponding stream generation unit 12 (12a, 12b, 12c, 12d) of the previous stage. Holds a stream of bandwidth. Specifically, each signal holding unit 13a, 13b, 13c, 13d has only 32000 bytes corresponding to two frames of a 100 Gbit band stream generated and input by the corresponding stream generation units 12a, 12b, 12c, 12d. Hold.

When one signal relay processing unit (any of 14a, 14b, 14c, 14d) is selected by the switching control of the signal monitoring unit 15, the signal relay processing unit 14 has 100 Gbit held in the corresponding signal holding unit 13. Read the band stream in the 400 Gbit band. For example, when the signal relay processing unit 14a is selected by the switching control of the signal monitoring unit 15, the signal relay processing unit 14a reads out the stream of the 100 Gbit band held by the corresponding signal holding unit 13a in the previous stage in the 400 Gbit band. That is, the signal relay processing unit 14a reads out the stream of the 100 Gbit band held by the corresponding signal holding unit 13a in units of 2048 bits at an operating clock frequency of 200 MHz. As a result, the signal relay processing unit 14a reads out a stream in the 100 Gbit band at a speed four times faster than that of the stream generation unit 12a at an operating clock frequency of 200 MHz. The other signal relay processing units 14b, 14c, and 14d are also subjected to the same processing when selected by the switching control of the signal monitoring unit 15.

Each signal relay processing unit 14a, 14b, 14c, 14d reads a stream in the 100 Gbit band from the corresponding signal holding units 13a, 13b, 13c, 13d in the 400 Gbit band, and controls at least the next switching with the signal monitoring unit 15. It has a function of notifying the target signal relay processing unit 14 of the end of a frame in the read stream.

In the present embodiment, in FIG. 2, the first-stage signal relay processing unit 14a sets the end of the frame in the stream read from the corresponding signal holding unit 13a to the signal monitoring unit 15 and the second-stage signal relay processing unit 14b. Notify to. The second-stage signal relay processing unit 14b notifies the signal monitoring unit 15 and the third-stage signal relay processing unit 14c of the end of the frame in the stream read from the corresponding signal holding unit 13b. The third-stage signal relay processing unit 14c notifies the signal monitoring unit 15 and the fourth-stage signal relay processing unit 14d of the end of the frame in the stream read from the corresponding signal holding unit 13c. The fourth-stage signal relay processing unit 14d notifies the signal monitoring unit 15 and the first-stage signal relay processing unit 14a of the end of the frame in the stream read from the corresponding signal holding unit 13d.

When each signal relay processing unit 14a, 14b, 14c, 14d reads a stream in the 100 Gbit band from the corresponding signal holding unit 13 in the 400 Gbit band, the end of the frame in the read stream is processed by signal relay processing other than itself. The unit 14 may be notified.

Further, each signal relay processing unit 14a, 14b, 14c, 14d is selectively switched and controlled by the signal monitoring unit 15, and when a stream in the 100 Gbit band is read from the corresponding signal holding unit 13 in the 400 Gbit band, the switching control is performed. It has a function to perform alignment so that the frame is not interrupted at a halfway position in the stream.

The signal monitoring unit 15 has a function of monitoring the holding state of a stream in a 100 Gbit band of each signal holding unit 13 (13a, 13b, 13c, 13d), and a plurality of signal relay processing units 14 (14a, 14b, 14c, 14d). It has a function of switching and controlling so as to select one signal relay processing unit (any of 14a, 14b, 14c, 14d) from among them.

Further explaining, the signal monitoring unit 15 has each signal holding unit 13a, 13b, 13c, 13d so that the 100 Gbit band stream held by each signal holding unit 13a, 13b, 13c, 13d is not exhausted and the buffer is not emptied. It constantly monitors whether or not the holding state of the stream of 100 Gbit band is maintained.

Further, when the signal monitoring unit 15 receives the notification of the end of the frame from the signal relay processing unit 14 (any of 14a, 14b, 14c, 14d) that is currently selected and switched, the signal monitoring unit 15 maintains the holding state of the stream in the 100 Gbit band. Switching control is performed so that one signal relay processing unit 14 is selected from the signal relay processing units 14 corresponding to the signal holding unit 13.

Further, in the present embodiment, the signal monitoring unit 15 switches and controls the signal relay processing unit 14a to be selected in the initial state, and the stream of the 100 Gbit band of each signal holding unit 13a, 13b, 13c, 13d. When the holding state is constantly monitored and the signal relay processing unit 14, which is currently selected and switched, notifies the end of the frame, the signal holding unit 13 confirms that the stream holding state is maintained, and then signals are relayed. The processing unit 14 is selected and switched in the order of 14a → 14b → 14c → 14d → 14a → ....

The timing of the switching control is the end position of the frame and the GAP when the signal relay processing unit 14 notifies the end of the frame. Further, in order to simplify the circuit configuration, the end of the frame is set to 8 byte units.

Further, when the signal holding unit 13 (13a, 13b, 13c, 13d) has a signal holding unit 13 in which the stream holding state is not maintained, the signal monitoring unit 15 displays the stream having the largest capacity. It is also possible to give priority to the holding signal holding unit 13 and selectively switch control the signal relay processing unit 14 corresponding to the signal holding unit 13.

The signal selection unit 16 has an operating clock frequency of 200 MHz as a 2048-bit stream obtained by ORing the effective streams from a plurality of signal relay processing units 14 (14a, 14b, 14c, 14d) that are sequentially switched and controlled. A stream of × 2048 bits is selectively output as a stream of a 400 Gbit band.

The signal output unit 17 processes the 400 Gbit band stream from the signal selection unit 16 for each layer such as MAC, PCS, and FEC and outputs the stream.

Returning to FIG. 1, the input / output unit 4 transmits a data frame of the test signal between the signal generation unit 3 and the object W to be measured, and the data of the test signal between the object W to be measured and the signal measurement unit 5. Receive a frame. The input / output unit 4 includes, for example, an optical transceiver module such as a QSFP-DD, a CFP8, or an OSFP, and includes an E / O converter and an O / E converter that mutually convert an electric signal and an optical signal.

For example, when an optical transceiver module of QSFP DD (DR4, LR4, FR4) is adopted, the 8-lane parallel electric signal generated by the signal generation unit 3 is converted into a 4-lane parallel optical signal to be measured. The 4-lane parallel optical signal from W is converted into an 8-lane parallel electric signal.

When the optical transceiver module of QSFP DD (LR8, FR8, SR8) is adopted, the 8-lane parallel electric signal generated by the signal generation unit 3 is converted into a 4-lane parallel optical signal to be measured. The 8-lane parallel optical signal from the object W is converted into an 8-lane parallel electric signal.

The signal measurement unit 5 performs various measurements including error detection based on the data frame of the electric signal converted by the optical transceiver module of the input / output unit 4. When performing error detection, for example, the signal measuring unit 5 sets a data frame (for example, 160-bit data) of an electric signal transmitted to the object W to be measured and an input / output unit 4 according to a preset timing set in the operation unit 2. The presence or absence of an error is detected by synchronizing with a data frame of an electric signal from the optical transceiver module (for example, 160-bit data) and comparing the bits. That is, the signal measuring unit 5 bit-compares the data frame transmitted to the measured object W and the data frame from the optical transceiver module of the input / output unit 4 received from the measured object W, and if both match, there is no error: If 0 and both do not match, there is an error: 1 and error detection is performed.

The setting timing is, for example, set in advance by the operation unit 2 on a setting screen (not shown) of the display unit 7, and is, for example, a timing for receiving data of a pattern matching a specific pattern including an error, and a measurement to be performed. This is the timing at which the object W generates the trigger signal, the timing at which the trigger signal is generated by the user's instruction (for example, button operation), and the timing at which an error is detected.

The control unit 6 is composed of, for example, a microcomputer including a CPU, ROM, RAM, etc., and controls each unit constituting the network test apparatus in an integrated manner, and is a data frame in the signal generation unit 3 based on the settings of the operation unit 2. Generation control, data frame transmission / reception control in the input / output unit 4, switching control of the switching unit 13 based on the setting of the operation unit 2, various measurement control in the signal measurement unit 5 based on the setting of the operation unit 2, to the display unit 7. Controls the display of the setting screen and measurement results.

The display unit 7 is composed of a display device such as a liquid crystal display or electroluminescence (EL), for example, displays a setting screen for performing various tests based on the operation of the operation unit 2, and various measurements by the signal measurement unit 5. Display the results.

Next, as a stream generation method of the network test apparatus 1 configured as described above, FIG. 3 shows an example of a method of bundling a plurality of 100 Gbit band streams and extending the transmission band to a 400 Gbit band stream to generate a stream. It will be explained with reference to it.

First, each stream generation unit 12a, 12b, 12c, 12d individually generates a stream having a 100 Gbit band (ST1).

Subsequently, each signal holding unit 13a, 13b, 13c, 13d individually holds a stream of a 100 Gbit band generated by the corresponding stream generation units 12a, 12b, 12c, 12d (ST2).

The signal monitoring unit 15 selectively switches and controls the initial state, that is, the signal relay processing unit 14 that first reads the stream (ST3). In the present embodiment, the signal monitoring unit 15 selectively switches and controls the signal relay processing unit 14a corresponding to the signal holding unit 13a as the signal relay processing unit 14 that first reads out the stream.

Then, the signal relay processing unit 14a, which is selectively switched and controlled by the signal monitoring unit 15, reads out the stream of the 100 Gbit band held by the corresponding signal holding unit 13a in the 400 Gbit band (ST4).

After that, the signal monitoring unit 15 constantly monitors the holding state of the stream of each signal holding unit 13a, 13b, 13c, 13d, and receives a notification of the end of the frame in the stream from the signal relay processing unit 14 currently selected and switched. Then, at the timing of receiving the notification of the end of this frame, the signal relay processing unit 14 that next reads the stream is selected and switched from the signal relay processing units 14 corresponding to the signal holding unit 13 that keeps the stream holding state. Control (ST5).

Then, the signal relay processing unit 14 whose selection is sequentially switched reads out the stream of the 100 Gbit band held by the corresponding signal holding unit 13 in the 400 Gbit band (ST6). At that time, the signal relay processing unit 14 performs alignment so that the frame is not interrupted at a halfway position in the stream at the time of switching control by the signal monitoring unit 15.

More specifically, in the present embodiment, the signal monitoring unit 15 controls the signal relay processing unit 14 in the order of 14a → 14b → 14c → 14d → 14a → .... Then, the signal relay processing unit 14 whose selection is switched in order reads the stream of the 100 Gbit band held by the corresponding signal holding unit 13 in the 400 Gbit band, and the frame is interrupted at a halfway position in the stream at the time of switching control. Align so that there is no such thing.

Then, the signal selection unit 16 obtains a 2048-bit stream obtained by ORing the effective streams from the signal relay processing units 14a, 14b, 14c, and 14d, which are sequentially selected and switched and controlled by the signal monitoring unit 15. Selectively output as a 400 Gbit band stream with an operating clock frequency of 200 MHz (ST7).

By the way, in the above-described embodiment, a configuration in which four each of the stream generation unit 12, the signal holding unit 13, and the signal relay processing unit 14 are provided to generate a stream having a 400 Gbit band has been described as an example, but the stream generation unit 12 has been described. , The signal holding unit 13 and the signal relay processing unit 14 may be provided at least two or more, and if the number is N, the Gbit band of the generated stream = 100 Gbit band stream × N (N ≧ 2). It becomes.

Further, in the above-described embodiment, after the signal monitoring unit 15 confirms that the stream holding state of the signal holding unit 13 is maintained, the signal relay processing unit 14 is moved to 14a → 14b → 14c → 14d → 14a → The case where the selection switching control is performed in the order of ... has been described as an example, but the order is not limited to this, and the signal relay processing unit 14 selected in the initial state may be any of 14a, 14b, 14c, and 14d. Then, after the signal relay processing unit 14 selected in the initial state reads the stream, the signal monitoring unit 15 constantly monitors the stream holding state of the signal holding unit 13 and receives a notification of the end of the frame. The signal relay processing unit 14 that reads the stream next at the same timing controls selection switching, and the signal relay processing unit 14 that has been selected and switched is aligned so that the frame is not interrupted at a halfway position in the stream during switching control. I do.

As described above, according to the present embodiment, as the stream generation circuit 11, it is possible to utilize a conventionally used circuit for generating a stream of 100 Gbit band and to expand the transmission band to generate the stream. It will be possible to easily and inexpensively respond to future increases in transmission rate.

Although the best form of the network test apparatus and the network test method according to the present invention has been described above, the present invention is not limited by the description and drawings in this form. That is, it goes without saying that all other forms, examples, operational techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

1 Network test equipment 2 Operation unit 3 Signal generation unit 4 Input / output unit 5 Signal measurement unit 6 Control unit 7 Display unit 11 Stream generation circuit 12 (12a, 12b, 12c, 12d) Stream generation unit 13 (13a, 13b, 13c, 13d) Signal holding unit 14 (14a, 14b, 14c, 14d) Signal relay processing unit 15 Signal monitoring unit 16 Signal selection unit 17 Signal output unit W Measured object (DUT)

Claims (2)

A data frame of a test signal generated corresponding to the communication standard of the object to be measured (W) is input to the object to be measured, and a data frame received from the object to be measured in accordance with the input of the data frame of the test signal. In the network test device (1) that measures various tests based on
A plurality of stream generators (12) that generate streams in the first bit band, and
A plurality of signal holding units (13) for holding a stream input from the corresponding stream generation unit among the plurality of stream generation units, and a plurality of signal holding units (13).
A plurality of signal relay processing units (14) for reading a stream held in the corresponding signal holding unit among the plurality of signal holding units in a second bit band larger than the first bit band.
The stream holding state of each of the plurality of signal holding units is monitored, and switching control is performed so as to select one signal relay processing unit from the signal relay processing units corresponding to the signal holding units that maintain the stream holding state. Signal monitoring unit (15) and
It is provided with a signal selection unit (16) that selects a valid stream read by the plurality of signal relay processing units in accordance with the switching control of the signal monitoring unit and sets the stream in the second bit band.
The signal relay processing unit notifies the signal monitoring unit and the signal relay processing unit to be the next switching control target of the end of the frame in the stream read in the second bit band from the corresponding signal holding unit, and the signal monitoring. Alignment is performed so that the frame is not interrupted in the stream during switching control by the unit.
The signal monitoring unit is characterized in that it switches and controls one signal relay processing unit from the signal relay processing units corresponding to the signal holding unit that maintains the holding state of the stream at the timing when the notification of the end of the frame is received. Network test equipment. A data frame of a test signal generated corresponding to the communication standard of the object to be measured (W) is input to the object to be measured, and a data frame received from the object to be measured in accordance with the input of the data frame of the test signal. In the network test method that measures various tests based on
A step of individually generating a stream of the first bit band by a plurality of stream generation units (12), and
A step of individually holding the streams individually generated by the plurality of stream generation units in the plurality of signal holding units (13), and
A step of reading a stream individually held by the plurality of signal holding units in a second bit band larger than the first bit band by the corresponding signal relay processing unit of the plurality of signal relay processing units (14). ,
A step of monitoring the holding state of the stream individually held by the plurality of signal holding units by the signal monitoring unit (15), and a step of monitoring each of them.
The signal relay processing for which the signal relay processing unit is subject to the next switching control with the signal monitoring unit for the end of a frame in the stream read in the second bit band from the corresponding signal holding unit among the plurality of signal holding units. Steps to notify the department and
A step of switching and controlling the signal relay processing unit corresponding to the signal holding unit that holds the stream holding state at the timing when the signal monitoring unit receives the notification of the end of the frame to one signal relay processing unit.
The step of aligning the frame so that the frame is not interrupted in the stream during the switching control, and
A network including a step of selecting a valid stream read by the plurality of signal relay processing units in accordance with switching control of the signal monitoring unit and converting it into a stream of the second bit band. Test method.

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