An example message exchange is shown in Fig. 2. In the example, the client performs a GET request (1) to a server, which acknowledges the request reception immediately (2)
to avoid re-transmissions. This operation mode is called separate.
Then, the server collects the document requested,possibly also contacting a remote server in case the resource is not stored locally.
When ready, it sends the response(3), with the request content embedded, to the client, whichcloses the exchange with an acknowledgment (4).
Messages(2) and (3) can be also sent a single message (piggyback mode), which in this case does not require the explicit acknowledgment in (4).