Create a connectionless socket

Connectionless sockets use User Datagram Protocol (UDP) instead of TCP/IP.

The following figure illustrates the client/server relationship from the socket APIs used in the code examples for a connectionless socket design.

Socket flow of events: Connectionless server

The following sequence of the socket calls provide a description of the figure and the following example programs. It also describes the relationship between the server and client application in a connectionless design. Each set of flows contain links to usage notes on specific APIs. If you need more details on the use of a particular API, you can use these links. The first example uses the following sequence of function calls:

1. The socket() function returns a socket descriptor representing an endpoint. The statement also identifies that the INET (Internet Protocol) address family with the UDP transport (SOCK_DGRAM) is used for this socket.
2. After the socket descriptor is created, a bind() function gets a unique name for the socket. In this example, the user sets the s_addr to zero, which means that the UDP port of 3555 is bound to all IPv4 addresses on the system.
3. The server uses the recvfrom() function to receive that data. The recvfrom() function waits indefinitely for data to arrive.
4. The sendto() function echoes the data back to the client.
5. The close() function ends any open socket descriptors.

Socket flow of events: Connectionless client

The second example uses the following sequence of function calls:

1. The socket() function returns a socket descriptor representing an endpoint. The statement also identifies that the INET (Internet Protocol) address family with the UDP transport (SOCK_DGRAM) is used for this socket.
2. In the client example program, if the server string that was passed into the inet_addr() function was not a dotted decimal IP address, then it is assumed to be the hostname of the server. In that case, use the gethostbyname() function to retrieve the IP address of the server.
3. Use the sendto() function to send the data to the server.
4. Use the recvfrom() function to receive the data back from the server.
5. The close() function ends any open socket descriptors.