Many of the programs in this directory are named according to the 
conventions described below.

A prefix identifies the socket domain in which the program operates, 
and the socket type employed. The socket domain is indicated by one
or two letters:

    u  UNIX
    i   Internet (both v4 and v6)
    i6  Internet v6 only

The socket type is one of the following:

    d   datagram
    s   stream

A suffix indicates whether the program is a client or server:

    cl client
    sv server

Thus, id_echo_sv.c is a server program that uses datagram sockets in 
the Internet domain.