Transmission Control Protocol for IP

See also: api

Common functions for the TCP implementation, such as functions for manipulating the data structures and the TCP timer functions. TCP functions related to input and output is found in tcp_in.c and tcp_out.c respectively.

TCP connection setup

The functions used for setting up connections is similar to that of the sequential API and of the BSD socket API. A new TCP connection identifier (i.e., a protocol control block - PCB) is created with the tcp_new() function. This PCB can then be either set to listen for new incoming connections or be explicitly connected to another host.

tcp_new()
tcp_bind()
tcp_listen() and tcp_listen_with_backlog()
tcp_accept()
tcp_connect()

Sending TCP data

TCP data is sent by enqueueing the data with a call to tcp_write() and triggering to send by calling tcp_output(). When the data is successfully transmitted to the remote host, the application will be notified with a call to a specified callback function.

tcp_write()
tcp_output()
tcp_sent()

Receiving TCP data

TCP data reception is callback based - an application specified callback function is called when new data arrives. When the application has taken the data, it has to call the tcp_recved() function to indicate that TCP can advertise increase the receive window.

tcp_recv()
tcp_recved()

Application polling

When a connection is idle (i.e., no data is either transmitted or received), lwIP will repeatedly poll the application by calling a specified callback function. This can be used either as a watchdog timer for killing connections that have stayed idle for too long, or as a method of waiting for memory to become available. For instance, if a call to tcp_write() has failed because memory wasn't available, the application may use the polling functionality to call tcp_write() again when the connection has been idle for a while.

tcp_poll()

Closing and aborting connections

tcp_close()
tcp_abort()
tcp_err()