StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>This is is indeed networking question, but it may be appropriate here after all.</p> <p>The confusion arises from distinction between packet-oriented and stream-oriented connections.</p> <p>Internet is often called "TCP/IP" network. At the low level (IP, Internet Protocol) the Internet is packet-oriented. Hosts send packets to other hosts.</p> <p>However, on top of IP we have TCP (Transmission Control Protocol). The entire purpose of this layer of the internet is to hide the packet-oriented nature of the underlying medium and to present the connection between two hosts (hosts and ports, to be more correct) as a stream of data, similar to a file or a pipe. We can then open a socket in the OS API to represent that connection, and we can treat that socket as a file descriptor (literally an FD in Unix, very similar to file HANDLE in Windows).</p> <p>Most of the rest of Internet client-server protocols (HTTP, Telnet, SSH, SMTP) are layered on top of TCP. Thus a client opens a connection (a socket), writes its request (which is transmitted as one or more pockets in the underlying IP) to the socket, reads the response from a socket (and the response can contain data from multiple IP packets as well) and then... Then the choice is to keep the connection open for the next request or to close it. Pre-KeepAlive HTTP always closed the connection. New clients and servers can keep it open.</p> <p>The advantage of KeepAlive is that establishing a connection is expensive. For short requests and responses it may take more packets than the actual data exchange.</p> <p>The slight disadvantage may be that the server now has to tell the client where the response ends. The server cannot simply send the response and close the connection. It has to tell the client: "read 20KB and that will be the end of my response". Thus the size of the response has to be known in advance by the server and communicated to the client as part of higher-level protocol (e.g. <code>Content-Length:</code> in HTTP). Alternatively, the server may send a delimiter to specify the end of the response - it all depends on the protocol above TCP.</p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload