BSD is modeled after the Unix file system interface and closely emulates the 4.3 BSD Socket Programming Interface. However, instead of opening a disk file, you create a socket and use its I/O handle to read, write, and close a socket similar to how you would read, write, and close a disk file. Because of the complex nature of network communications, your application must invoke several operations that are not required by the Unix file system interface. Instead of a filename, each socket that an application creates has a unique network address. To send data, your application must supply the address of the destination socket.