每一次请求都要在网络上传输一些数据；如果请求未在服务器上发现任何更新，那么这个数据传输就是浪费的。

Each request carries some data over the network; if the request does not find any updates on the server, this data transfer is a waste.

youdao

相反，您必须发起一个传输请求将数据复制到本地存储中。

Instead, you must initiate a transfer request to copy data into your local store.

youdao

在普通HTTP通信中，客户端始终通过打开到服务器的连接并发送请求来发起数据传输。

In normal HTTP communication, the client always initiates the data transfer by opening a connection to the server and sending a request.

youdao