This is only understood from the perspective of Internet services.
Summary: Dial test is a test method of network link quality. Dial test is very similar to crawlers, and more accurately, it is very similar to hackers controlling "broilers" to launch DDos attacks. The "broiler" here is the client of a certain Internet service, such as PC and mobile.
Purpose: To detect the link status of users in various regions to various service access points, so that the service scheduling system can provide users with the best access points based on the detection results.
Note: Dial test will take up network resources and should be performed during idle time; dial test will also consume "broiler" network traffic, but there are generally restrictions, such as mobile phones are limited to a few hundred KB to avoid being discovered by users.