IAX Settings

IAX stands for Inter-Asterisk eXchange protocol. IAX uses a single port for call signaling and transmission of a VoIP audio stream while SIP uses multiple different ports for signalling and audio traffic. The IAX default port configuration is UDP port (4569).

The IAX Settings page defines the rules that your UCx will use to establish IAX connections to other devices and servers.
To access your IAX Settings page, perform the following steps:

  1. Open the UCX Web-based Configuration Utility
  2. From the PBX tab, select PBX Configuration
  3. From the left side column, under Settings, select IAX Settings

Audio Codecs

Field Description
Codecs Check the desired codecs, all others will be disabled unless explicitly enabled in a device or trunk configuration. Drag to re-order.
Codec Priority Controls the codec negotiation of an inbound IAX call. This option is inherited by all entities and can also be defined in each entity which will override the setting here. Valid values are:
  • host - consider the host's preferred order ahead of the caller's
  • caller - consider the caller's preferred order ahead of the host's
  • disabled - disable the consideration of codec preference
  • regonly - same as disabled, but do not consider capabilities if the requested format is not available, i.e. call will only be accepted if the requested format is available
Bandwidth Specify the bandwidth to control which codecs are used in general. Valid values are:
  • low
  • medium
  • high
  • unset

Video Codecs

Field Description
Video Support Click to enable or disable video support and select the desired codecs when Enabled.
Drag to re-order.
  • h264 - most commonly used format for HD video
  • h263p - an enhanced version of H.263 with better video quality
  • h263 - lower bit rates designed for video conferencing
  • h261 - obsolete but remains for backwards compatibility


Registration Settings

Field Description
Registration Times Defines the Minimum and Maximum length of time that IAX peers can request as a registration expiration interval in seconds.
  • minregexpire - default 60
  • maxregexpire - default 3600

Jitter Buffer Settings

Field Description
Jitter Buffer Click to enable or disable jitter buffer. When Enabled, you can adjust several parameters relating to jitter buffer to compensate for varying network delays.
Jitter buffer works for incoming audio, outbound audio will be managed by the jitter buffer at the other end.
Force Jitter Buffer When Enabled, it will force the use of jitter buffer on the receiving side of an IAX channel. Avoid enabling this in the middle of a VoIP call path, as you may end up having two jitter buffers, adding too much latency into the stream, 
Jitter Buffer Size maxjitterbuffer - Max length of the jitter buffer in milliseconds.
resyncthreshold - When the jitter buffer notices a significant change in delay that continues over a few frames, it will resync, assuming that the change in delay was caused by a timestamping mix-up. The threshold for noticing a change in delay is measured as twice the measured jitter plus this resync threshold. Resyncing can be disabled by setting this parameter to -1.
Max Interpolations The maximum number of interpolation frames the jitter buffer should return in a row. Since some clients do not send CNG/DTX frames to indicate silence, the jitter buffer will assume silence has begun after returning this many interpolations. This prevents interpolating throughout a long silence.

Advanced General Settings

Field Description
Language The default language for a channel
Bind Address The IP address to bind to and listen for calls on the bind port. If set to, Asterisk will listen on all addresses. To bind to multiple IP addresses or ports, use the “Other IAX Settings” field below where you can put a setting such as “bindaddr=” It is recommended to leave this blank.
Bind Port Local incoming UDP port that Asterisk will bind to and is listed for IAX messages. The IAX standard is “4569” and in most cases this is what you want. It is recommended to leave this blank.
Delay Auth Rejects For increased security against brute force password attacks, enable this to delay the sending of authentication reject for REGREQ or AUTHREP if there is a password.
Other IAX Settings You may set any other IAX setting not present on this page. There will be no error checking against these settings, so check them carefully. They should be entered as “[setting] = [value]” in the available boxes. Click the Add field box to add additional fields. Blank boxes will be deleted when submitted.

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