The best way to find the ideal datagram size is to do exactly what TCP itself does to find the ideal packet size: Path MTU discovery. TCP also has a widely used option where both sides tell the other what their MSS (basically, MTU minus headers) is.
In theory SMTP can be handled by either TCP, UDP, or some 3rd party protocol. As defined in RFC 821, RFC 2821, and RFC 5321: SMTP is independent of the particular transmission subsystem and requires only a reliable ordered data stream channel. In addition, the Internet Assigned Numbers Authority has allocated port 25 for both … Read more
Strictly speaking, packet duplication in IP network is allowed behavior of the network and you have to be able to deal with it in your software even if you will somehow get rid of it this time. If you are just wondering about why this happens in your particular case… at a first glance I … Read more
accept() is for TCP. It has nothing to do with UDP. connect() in UDP doesn’t do anything to the other end, it just conditions the local API to know who you are sending to and receiving from. If you don’t already know that, or don’t care, or want to send to multiple destinations with the … Read more
You can bind to a port multiple times using the ReuseAddress socket option. UdpClient udpClient = new UdpClient(); udpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true); You’ll need to set the same option on the UDP server socket as well.
The SO_RCVTIMEO option expects a struct timeval defined in sys/time.h, not an integer like you’re passing to it. The timeval struct has as field for seconds and a field for microseconds. To set the timeout to 100ms, the following should do the trick: struct timeval tv; tv.tv_sec = 0; tv.tv_usec = 100000; if (setsockopt(rcv_sock, SOL_SOCKET, … Read more
The interface/API presented to you the user(programmer) of these protocols are: UDP Message oriented, you have an API (send/recv and similar) that provide you with the ability to send one datagram, and receive one datagram. 1 send() call results in 1 datagram sent, and 1 recv() call will recieve exactly 1 datagram. TCP Stream oriented, … Read more
No, you can’t. TCP is a protocol for communication between exactly two endpoints. Compared to UDP it features reliable transport, that means, that packets get not only send, but it is expected that the peer acknowledges the receipt of the data and that data will be retransmitted if the acknowledgment is missing. And because Broadcast … Read more
Then what is the point of UDP when we already have IP? To multiplex services. The UDP port number can differentiate between multiple services on the same host, using the same L3 identification. Using IP only it wouldn’t be possible to host multiple services on the same station and easily differentiate between them. Also, consider … Read more
Hello from the distant future which is the year 2018, to the year 2012. There’s, in fact, a reason behind connect()ing an UDP socket in practice (though blessed POSIX and its implementations don’t in theory require you to). An ordinary UDP socket doesn’t know anything about its future destinations, so it performs a route lookup … Read more