<p>I'm just curious about this question, can any one tell me?</p>

<p>TCP is a streaming protocol between a server and clients. The protocol is reliable and requires separate state for each server<>client stream. The connect protocol, initiated with listen/accept, sets up this server<>client connection state. UDP is a connectionless, unreliable datagram, (message) protocol, so no need to listen for new connections - datagrams can come in in any order from any source.</p>

Why the listen() function call is not needed when use UDP socket?

1 Answers

TCP is a streaming protocol between a server and clients. The protocol is reliable and requires separate state for each server<>client stream. The connect protocol, initiated with listen/accept, sets up this server<>client connection state. UDP is a connectionless, unreliable datagram, (message) protocol, so no need to listen for new connections - datagrams can come in in any order from any source.