Can you please explain the following steps in detail in the the tcp_echoclient example.
/* pass newly allocated es structure as argument to tpcb */
tcp_arg(tpcb, es);
/* initialize LwIP tcp_recv callback function */
tcp_recv(tpcb, tcp_echoclient_recv);
/* initialize LwIP tcp_sent callback function */
tcp_sent(tpcb, tcp_echoclient_sent);
/* initialize LwIP tcp_poll callback function */
tcp_poll(tpcb, tcp_echoclient_poll, 1);
/* send data */
tcp_echoclient_send(tpcb,es);
