Test example・Aging test on poor quality channels

21/09/2021Test qualityy

If there is a communication function with the outside, aging on a poor quality communication path is also important.

In order to confirm the stable operation of the embedded software, it is necessary to confirm the operation of the embedded software in various states . Following the startup test , secondary storage degradation test, and high-load aging test that focus on startup processing , this article introduces the need for aging tests on poor quality channels . Communication errors , communication delays , data loss , response delays from servers, etc. occur in poor quality communication channels . Aging tests on poor quality channels confirm the stability of the equipment when such a situation occurs.

The communication path in the test environment is very clean and comfortable

If the embedded device has a communication function, the test items will naturally include a test related to that communication function . Various features and performance tests will be planned. However, perform their test test environment is prepared communication channel for testing and the level of the communication device that is prepared for the test (in the case of most server on the other side of the network) now being built using the ..

The communication path prepared for this test is made up of communication cables and communication equipment (hubs, modems, etc.) installed in the test room, so it is securely connected with a short cable , and the quality of the communication path is Very good . There will be almost no signal deterioration due to cables , noise contamination , or signal interruptions due to poor contact . In addition, the high-level communication equipment prepared for the test is also operating with a margin because it only deals with the other party to be tested .

The communication channel in the production environment is wilder than you can imagine

However, there are various production environments in which embedded devices are actually used . Even if the metal channel even if the light (copper wire), the communication device of the upper which is a counterpart of communication is installed in production from the station built device location that is placed up, long A communication cable is pulled over the distance , and there are many branches and signal converters in the middle . Long cables may be affected by noise on the way, and if the cable connection point is underground, it will be vibrated by the running of a large drag, and if it is an overhead wire in the air, it will be shaken by a strong wind due to a typhoon, causing poor contact at the connection part. It is possible to do it.

Even if it is a high-end communication device, even though it is composed of a load balancer and a large number of servers , the entire system is designed on the assumption that it will provide services to many users with best effort . Therefore, sometimes the load is concentrated beyond the design capacity, and the response may be severely delayed or the response may not be returned . In short, in a production environment , both the communication path itself and the higher-level communication equipment can be very wild compared to the test environment .

The wireless LAN function cannot avoid interference in the production environment.

In addition, recent built-in device function of the wireless LAN , but is often marked with, when there is a wireless LAN function is interference in the radio section often is also the actual operation that takes place is. In the test environment, an environment is created in which the wireless connection can be made stably so that the functions using the wireless LAN can be confirmed to operate correctly . However, in the production environment where the embedded device is actually placed , there are cases where the wireless connection is frequently cut off due to interference from the radio waves of other stations .

In particular, WiFi and Bluetooth, which use 2.4GHz radio waves, are flooded with many devices even in ordinary living spaces these days. For wireless LAN routers, there are times when overseas products with high output that exceed the upper limit of output regulated by Japanese wireless regulations are used in the vicinity, and when such products and communication channels overlap, wireless communication There is also a situation where it cuts sharply .

Communication delay, packet loss, communication error, and communication interruption occur in the actual communication path.

In this way, if the production environment is a poor quality communication path , data loss or signal weakening due to temporary disconnection due to poor contact in the physical layer of communication (hard communication path such as optical cable or copper wire) And noise causes transmission errors . Errors in these physical layers are detected in the upper protocol layer and error recovery processing such as retransmission is executed. If the error recovery process is successful, the data will be correctly passed to the higher-level application software, but there will be a delay due to the time required for the resend process . If the error is not recovered even after resending, an error response such as packet loss or loss of connection status will be returned to the higher-level application software . As a result, the app will execute the corresponding semi-normal processing.

Sometimes the server on the other side of the production channel is out of order.

In a production environment, the servers on the other side of the communication path are not always in a state where they can afford it. Also service the beginning there was a surplus in processing capacity in a small number of users server, of the time is just prior to a growing number service subscribers will require server enhancement, are somehow operating at high load conditions also state that happen. When it hits the rapid increase of the load due to the time zone or there is a big event at such time, server processing beyond the physical load and the Sister Islands. As a result, processing may be discarded due to processing delay or timeout within the server .

When viewed from the embedded device side, processing delays and processing discards inside the server are often seen as timeouts or loss of responses for processing requests issued via the communication channel. You will have to do it.

Create a poor quality communication path and perform an aging test so that multiple errors occur at the same time.

As introduced so far, if you deal with a poor quality communication path or server, the embedded software will execute a lot of quasi-normal processing . This quasi-normal system processing is a test that is difficult to cover because the number of tests will explode immediately when trying to cover various combinations of errors .

That is why it is possible to occur in the production environment by preparing a poor quality communication path or server , creating an operating environment similar to the production environment where the embedded device is actually used , and performing a long-term aging test there. It is important to create as many states as possible where various sexual errors occur at the same time and at various timings, and to confirm stable operation.

Use jigs to make poor quality communication channels

Special equipment is required to create a poor quality communication path in the test environment . In order to lower the quality of the physical channel, even when the electrical signal even in the case of optical signals, attenuator lowers the strength of the signal , such as to connect momentarily cut or signals also soon instantaneous interruption simulator as Special jigs (tools made for special purposes) are required. To mix noise into a signal, you need a noise generator that produces the mixed noise and a mixer that mixes the signal and noise .

To reduce the quality at the packet level, you need a network simulator or delay simulator device that has the ability to delay or drop specific packets . It is relatively easy to reduce the responsiveness of the server, and it is a special load that physically reduces the memory of the server to reduce the processing performance, or consumes a large amount of CPU and memory to put a load on it. All you have to do is create an app and run it.

Think about the quality of the communication path, packet, and server, and think about the test plan.

Various jigs and test equipment are required to prepare poor quality communication channels and servers in the test environment. So, the communication path, packet, such as a server response whether the drop to what extent the quality of which part go-between to, and consideration at the stage of test plan prepare the necessary fixtures and equipment will need to keep increase. Once you have a plan for the equipment you need, think about a combination of quality deterioration settings such as what quality to reduce and how much time to age, and test time according to the purpose of the test, and follow it. Let’s carry out an aging test on a poor quality communication path.

Next to the test on the poor quality channel is the hard resource depletion test.

In the aging test in which a poor quality communication path was prepared, the stability was confirmed by giving an error from the outside of the embedded device and operating the quasi-normal system of the embedded software. It is hardware resource depletion that causes an error inside the embedded software, not outside. In the next article, I will introduce the hardware resource depletion error.

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Posted by グータラ親父