PBX and Bridges

PBX Engines And Bridges

PBX engines execute dialplans. Bridge modules connect channels once call setup has selected both sides of a call.

PBX Engines

Module	Source	Purpose
pbx_config.so	pbx/pbx_config.c	Classic extensions.conf dialplan engine.
pbx_ael.so	pbx/pbx_ael.c	AEL dialplan engine.
pbx_lua.so	pbx/pbx_lua.c	Lua dialplan support.
pbx_realtime.so	pbx/pbx_realtime.c	Realtime PBX switch.
pbx_spool.so	pbx/pbx_spool.c	Outgoing spool call files.
pbx_loopback.so	pbx/pbx_loopback.c	Loopback switch.
pbx_dundi.so	pbx/pbx_dundi.c	DUNDi support.

Important config files:

configs/extensions.conf.sample
configs/extensions.ael.sample
configs/extensions.lua.sample
configs/dundi.conf.sample

Bridge Modules

Module	Source	Purpose
bridge_simple.so	bridges/bridge_simple.c	Simple two-party bridge behavior.
bridge_softmix.so	bridges/bridge_softmix.c	Softmix bridge for conferences/mixing.
bridge_multiplexed.so	bridges/bridge_multiplexed.c	Multiplexed bridge technology.
bridge_builtin_features.so	bridges/bridge_builtin_features.c	Built-in bridge features.

Dialplan Configuration

Classic dialplan:

/etc/gabpbx/extensions.conf

Example:

[internal]
exten => 100,1,Dial(SIP/phone100,30)
same => n,Hangup()

With chan_sofia, the public channel name remains SIP, so existing dialplan syntax stays compatible.

Bridge Role In SIP Calls

For SIP calls, channel drivers handle signaling and media negotiation; bridge modules handle channel-to-channel media flow after call setup.

Transfers, direct media decisions, hold behavior, call recording and call features all interact with bridge state, so bridge behavior is central to production SIP correctness.