# &adminguide;

## Overview

The proto_tcp module is a built-in transport module which implements SIP TCP-based communication. It does not handle TCP connections management, but only offers higher-level primitives to read and write SIP messages over TCP.

Once loaded, you will be able to define TCP listeners in your script, by adding its IP, and optionally the listening port, in your configuration file, similar to this example:

    ...
    listen=tcp:127.0.0.1 		# change the listening IP
    listen=tcp:127.0.0.1:5080	# change with the listening IP and port
    ...

## Dependencies

### &osips; Modules

The following modules must be loaded before this module:

- None.

### External Libraries or Applications

The following libraries or applications must be installed before running &osips; with this module loaded:

- None.

## Exported Parameters

### `tcp_port` (integer)

The default port to be used by all TCP listeners.

Default value is 5060.

#### Set `tcp_port` parameter

    ...
    modparam("proto_tcp", "tcp_port", 5065)
    ...

### `tcp_send_timeout` (integer)

Time in milliseconds after a TCP connection will be closed if it is not available for blocking writing in this interval (and &osips; wants to send something on it).

Default value is 100 ms.

#### Set `tcp_send_timeout` parameter

    ...
    modparam("proto_tcp", "tcp_send_timeout", 200)
    ...

### `tcp_max_msg_chunks` (integer)

The maximum number of chunks that a SIP message is expected to arrive via TCP. If a packet is received more fragmented than this, the connection is dropped (either the connection is very overloaded and this leads to high fragmentation - or we are the victim of an ongoing attack where the attacker is sending the traffic very fragmented in order to decrease our performance).

Default value is 4.

#### Set `tcp_max_msg_chunks` parameter

    ...
    modparam("proto_tcp", "tcp_max_msg_chunks", 8)
    ...

### `tcp_crlf_pingpong` (integer)

Send CRLF pong (\r\n) to incoming CRLFCRLF ping messages over TCP. By default it is enabled (1).

Default value is 1 (enabled).

#### Set `tcp_crlf_pingpong` parameter

    ...
    modparam("proto_tcp", "tcp_crlf_pingpong", 0)
    ...

### `tcp_crlf_drop` (integer)

Drop CRLF (\r\n) ping messages. When this parameter is enabled, the TCP layer drops packets that contains a single CRLF message. If a CRLFCRLF message is received, it is handled according to the tcp_crlf_pingpong parameter.

Default value is 0 (disabled).

#### Set `tcp_crlf_drop` parameter

    ...
    modparam("proto_tcp", "tcp_crlf_drop", 1)
    ...

### `tcp_async` (integer)

If the TCP connect and write operations should be done in an asynchronous mode (non-blocking connect and write). If disabled, OpenSIPS will block and wait for TCP operations like connect and write.

Default value is 1 (enabled).

#### Set `tcp_async` parameter

    ...
    modparam("proto_tcp", "tcp_async", 0)
    ...

### `tcp_async_max_postponed_chunks` (integer)

If tcp_async is enabled, this specifies the maximum number of SIP messages that can be stashed for later/async writing. If the connection pending writes exceed this number, the connection will be marked as broken and dropped.

Default value is 32.

#### Set `tcp_async_max_postponed_chunks` parameter

    ...
    modparam("proto_tcp", "tcp_async_max_postponed_chunks", 16)
    ...

### `tcp_async_local_connect_timeout` (integer)

If tcp_async is enabled, this specifies the number of milliseconds that a connect will be tried in blocking mode (optimization). If the connect operation lasts more than this, the connect will go to async mode and will be passed to TCP MAIN for polling.

Default value is 100 ms.

#### Set `tcp_async_local_connect_timeout` parameter

    ...
    modparam("proto_tcp", "tcp_async_local_connect_timeout", 200)
    ...

### `tcp_async_local_write_timeout` (integer)

If tcp_async is enabled, this specifies the number of milliseconds that a write op will be tried in blocking mode (optimization). If the write operation lasts more than this, the write will go to async mode and will be passed to TCP MAIN for polling.

Default value is 10 ms.

#### Set `tcp_async_local_write_timeout` parameter

    ...
    modparam("proto_tcp", "tcp_async_local_write_timeout", 100)
    ...