The maximum concurrency number of browsers is 6, in order to avoid a large number of requests to deplete system resources, so minimize the number of interface requests and merge interface requests. The maximum number of concurrency is for the same domain name, so you can also request it by different domain names. It is common to open multiple tabs on a website at the same time. Multiple tabs share the 6 connection numbers, and the tab pages behind will be blocked and cannot be opened.