* sockets -- especially UDP

    - difference between TCP and UDP
        TCP -- connection oriented; stream oriented
               reliable but might not be timely
            socket
            bind
            listen
            accept
                then read/write or send/recv
        UDP -- message oriented
               unreliable but usually more timely
            socket
            bind
                recvfrom/recvmsg or sendto/sendmsg
    - in practice
        stream -- server listens for connections
                  accept a client connection (new fd)
                  bi-direction data flow on that fd
                    recv or read
                    send or write
        datagram -- server just binds to addr/port
                  uses recv* (e.g., recvmsg)
                  each message can come from a different client
                  only difference between a server and a typical client
                  is that the server binds to a well know port and the
                  client doesn't (it usually just gets one assigned)
                  typically would use
                    recvfrom or recvmsg
                    sendto or sendmsg

* handling multiple clients

    - TCP -- use poll across all client fds + accept fd to figure
             out which ones to read from
    - UDP -- use recvfrom/recvmsg to get a dgram + sender's address
             use a data structure to keep track of active client addrs