PROTO_TCP module
Admin Guide
Section titled “Admin Guide”Overview
Section titled “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 IPlisten=tcp:127.0.0.1:5080 # change with the listening IP and port...Dependencies
Section titled “Dependencies”OpenSIPS Modules
Section titled “OpenSIPS Modules”The following modules must be loaded before this module:
- None.
External Libraries or Applications
Section titled “External Libraries or Applications”The following libraries or applications must be installed before running OpenSIPS with this module loaded:
- None.
Exported Parameters
Section titled “Exported Parameters”tcp_port (integer)
Section titled “tcp_port (integer)”The default port to be used by all TCP listeners.
Default value is 5060.
...modparam("proto_tcp", "tcp_port", 5065)...tcp_send_timeout (integer)
Section titled “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 OpenSIPS wants to send something on it).
Default value is 100 ms.
...modparam("proto_tcp", "tcp_send_timeout", 200)...tcp_max_msg_chunks (integer)
Section titled “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.
...modparam("proto_tcp", "tcp_max_msg_chunks", 8)...tcp_crlf_pingpong (integer)
Section titled “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).
...modparam("proto_tcp", "tcp_crlf_pingpong", 0)...tcp_crlf_drop (integer)
Section titled “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).
...modparam("proto_tcp", "tcp_crlf_drop", 1)...tcp_async (integer)
Section titled “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).
...modparam("proto_tcp", "tcp_async", 0)...tcp_async_max_postponed_chunks (integer)
Section titled “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.
...modparam("proto_tcp", "tcp_async_max_postponed_chunks", 16)...tcp_async_local_connect_timeout (integer)
Section titled “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.
...modparam("proto_tcp", "tcp_async_local_connect_timeout", 200)...tcp_async_local_write_timeout (integer)
Section titled “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.
...modparam("proto_tcp", "tcp_async_local_write_timeout", 100)...Frequently Asked Questions
Section titled “Frequently Asked Questions”Q: After switching to OpenSIPS 2.1, I’m getting this error: “listeners found for protocol tcp, but no module can handle it”
You need to load the “proto_tcp” module. In your script, make sure you do a loadmodule “proto_tcp.so” after setting the mpath.
Q: I cannot locate “proto_tcp.so”. Where is it?
The “proto_udp” and “proto_tcp” modules are simply built into the opensips binary by default. They are not available as shared libraries, but look like modules for code consistency reasons.
Contributors
Section titled “Contributors”By Commit Statistics
Section titled “By Commit Statistics”Top contributors by DevScore(1), authored commits(2) and lines added/removed(3)
| # | Name | DevScore | Commits | Lines++ | Lines— |
|---|---|---|---|---|---|
| 1. | Bogdan-Andrei Iancu (@bogdan-iancu) | 61 | 25 | 2249 | 1017 |
| 2. | Razvan Crainea (@razvancrainea) | 25 | 16 | 796 | 98 |
| 3. | Stefan Darius (@dariusstefan) | 7 | 3 | 285 | 44 |
| 4. | Vlad Paiu (@vladpaiu) | 5 | 3 | 17 | 11 |
| 5. | Liviu Chircu (@liviuchircu) | 4 | 2 | 3 | 3 |
| 6. | Julián Moreno Patiño | 3 | 1 | 6 | 6 |
(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)
(2) including any documentation-related commits, excluding merge commits
(3) ignoring whitespace edits, renamed files and auto-generated files
By Commit Activity
Section titled “By Commit Activity”| # | Name | Commit Activity |
|---|---|---|
| 1. | Stefan Darius (@dariusstefan) | Jun 2026 - Jul 2026 |
| 2. | Razvan Crainea (@razvancrainea) | Jan 2015 - Jun 2026 |
| 3. | Liviu Chircu (@liviuchircu) | Apr 2015 - May 2016 |
| 4. | Julián Moreno Patiño | Feb 2016 - Feb 2016 |
| 5. | Bogdan-Andrei Iancu (@bogdan-iancu) | Feb 2015 - Mar 2015 |
| 6. | Vlad Paiu (@vladpaiu) | Mar 2015 - Mar 2015 |
(1) including any documentation-related commits, excluding merge commits
Documentation
Section titled “Documentation”Contributors
Section titled “Contributors”Last edited by: Razvan Crainea (@razvancrainea), Liviu Chircu (@liviuchircu), Bogdan-Andrei Iancu (@bogdan-iancu).
License
Section titled “License”All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0