This file is indexed.

/etc/dahdi/system.conf is in dahdi-linux 1:2.11.1~dfsg-1ubuntu4.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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#
# DAHDI Configuration File
#
# This file is parsed by the DAHDI Configurator, dahdi_cfg
#
# Span Configuration
# ^^^^^^^^^^^^^^^^^^
# First come the span definitions, in the format
# 
#   span=<span num>,<timing source>,<line build out (LBO)>,<framing>,<coding>[,yellow]
#
# All T1/E1/BRI spans generate a clock signal on their transmit side. The
# <timing source> parameter determines whether the clock signal from the far
# end of the T1/E1/BRI is used as the master source of clock timing. If it is, our
# own clock will synchronise to it. T1/E1/BRI connected directly or indirectly to
# a PSTN provider (telco) should generally be the first choice to sync to. The
# PSTN will never be a slave to you. You must be a slave to it.
#
# Choose 1 to make the equipment at the far end of the E1/T1/BRI link the preferred
# source of the master clock. Choose 2 to make it the second choice for the master
# clock, if the first choice port fails (the far end dies, a cable breaks, or
# whatever). Choose 3 to make a port the third choice, and so on. If you have, say,
# 2 ports connected to the PSTN, mark those as 1 and 2. The number used for each
# port should be different.
#
# If you choose 0, the port will never be used as a source of timing. This is
# appropriate when you know the far end should always be a slave to you. If
# the port is connected to a channel bank, for example, you should always be
# its master. Likewise, BRI TE ports should always be configured as a slave.
# Any number of ports can be marked as 0.
#
# Incorrect timing sync may cause clicks/noise in the audio, poor quality or failed
# faxes, unreliable modem operation, and is a general all round bad thing.
#
# The line build-out (or LBO) is an integer, from the following table:
#
#  0: 0 db (CSU) / 0-133 feet (DSX-1)
#  1: 133-266 feet (DSX-1)
#  2: 266-399 feet (DSX-1)
#  3: 399-533 feet (DSX-1)
#  4: 533-655 feet (DSX-1)
#  5: -7.5db (CSU)
#  6: -15db (CSU)
#  7: -22.5db (CSU)
#
# If the span is a BRI port the line build-out is not used and should be set
# to 0.
#
# framing:: 
#   one of 'd4' or 'esf' for T1 or 'cas' or 'ccs' for E1. Use 'ccs' for BRI.
#  'd4' could be referred to as 'sf' or 'superframe'
#
# coding:: 
#   one of 'ami' or 'b8zs' for T1 or 'ami' or 'hdb3' for E1. Use 'ami' for
#   BRI.
#
#   * For E1 there is the optional keyword 'crc4' to enable CRC4 checking.
#   * If the keyword 'yellow' follows, yellow alarm is transmitted when no
#     channels are open.
#
#span=1,0,0,esf,b8zs
#span=2,1,0,esf,b8zs
#span=3,0,0,ccs,hdb3,crc4
#
# Dynamic Spans
# ^^^^^^^^^^^^^
# Next come the dynamic span definitions, in the form:
# 
#   dynamic=<driver>,<address>,<numchans>,<timing>
#
# Where <driver> is the name of the driver (e.g. eth), <address> is the
# driver specific address (like a MAC for eth), <numchans> is the number
# of channels, and <timing> is a timing priority, like for a normal span.
# use "0" to not use this as a timing source, or prioritize them as
# primary, secondard, etc.  Note that you MUST have a REAL DAHDI device
# if you are not using external timing.
#
#   dynamic=eth,eth0/00:02:b3:35:43:9c,24,0
#
# If a non-zero timing value is used, as above, only the last span should
# have the non-zero value. 
#
# Channel Configuration
# ^^^^^^^^^^^^^^^^^^^^^
# Next come the definitions for using the channels.  The format is:
# <device>=<channel list>
#
# Valid devices are:
#
# e&m::
#   Channel(s) are signalled using E&M signalling (specific
#   implementation, such as Immediate, Wink, or Feature Group D
#   are handled by the userspace library).
# fxsls:: 
#   Channel(s) are signalled using FXS Loopstart protocol.
# fxsgs:: 
#   Channel(s) are signalled using FXS Groundstart protocol.
# fxsks:: 
#   Channel(s) are signalled using FXS Koolstart protocol.
# fxols:: 
#   Channel(s) are signalled using FXO Loopstart protocol.
# fxogs:: 
#   Channel(s) are signalled using FXO Groundstart protocol.
# fxoks:: 
#   Channel(s) are signalled using FXO Koolstart protocol.
# sf:: 
#   Channel(s) are signalled using in-band single freq tone. 
#   Syntax as follows: 
#    
#     channel# => sf:<rxfreq>,<rxbw>,<rxflag>,<txfreq>,<txlevel>,<txflag>
#   
#   rxfreq is rx tone freq in Hz, rxbw is rx notch (and decode)
#   bandwith in hz (typically 10.0), rxflag is either 'normal' or
#   'inverted', txfreq is tx tone freq in hz, txlevel is tx tone 
#   level in dbm, txflag is either 'normal' or 'inverted'. Set 
#   rxfreq or txfreq to 0.0 if that tone is not desired.
#
# unused:: 
#   No signalling is performed, each channel in the list remains idle
# clear::
#   Channel(s) are bundled into a single span.  No conversion or
#   signalling is performed, and raw data is available on the master.
# bchan:: 
#   Like 'clear' except all channels are treated individually and
#   are not bundled.  'inclear' is an alias for this.
# rawhdlc::
#   The DAHDI driver performs HDLC encoding and decoding on the 
#   bundle, and the resulting data is communicated via the master
#   device.
# dchan::
#   The DAHDI driver performs HDLC encoding and decoding on the
#   bundle and also performs incoming and outgoing FCS insertion
#   and verification.  'fcshdlc' is an alias for this. 
# hardhdlc::
#   The hardware driver performs HDLC encoding and decoding on the
#   bundle and also performs incoming and outgoing FCS insertion
#   and verification.  Is subject to limitations and support of underlying
#   hardware. BRI spans serviced by the wcb4xxp driver must use hardhdlc
#   channels for the signalling channels. 
# nethdlc::
#   The DAHDI driver bundles the channels together into an
#   hdlc network device, which in turn can be configured with
#   sethdlc (available separately). In 2.6.x kernels you can also optionally
#   pass the name for the network interface after the channel list.
#   Syntax:
#   
#     nethdlc=<channel list>[:interface name]
#   Use original names, don't use the names which have been already registered 
#   in system e.g eth.
#
# dacs::
#   The DAHDI driver cross connects the channels starting at
#   the channel number listed at the end, after a colon
# dacsrbs::
#   The DAHDI driver cross connects the channels starting at
#   the channel number listed at the end, after a colon and 
#   also performs the DACSing of RBS bits
#
# The channel list is a comma-separated list of channels or ranges, for
# example:
#
#   1,3,5 (channels one, three, and five)
#   16-23, 29 (channels 16 through 23, as well as channel 29)
#
# So, some complete examples are:
#
#   e&m=1-12
#   nethdlc=13-24
#   fxsls=25,26,27,28
#   fxols=29-32
#
# An example of BRI port:
# 
#   span=1,1,0,ccs,ami
#   bchan=1,2
#   hardhdlc=3
#
# NOTE: When using BRI channels in asterisk, use the bri_cpe, bri_net, or
# bri_cpe_ptmp (for point to multipoint mode). libpri does not currently
# support point to multipoint when in NT mode. Otherwise, the bearer channel
# are configured identically to other DAHDI channels.
#
#fxoks=1-24
#bchan=25-47
#dchan=48
#fxols=1-12
#fxols=13-24
#e&m=25-29
#nethdlc=30-33
#clear=44
#clear=45
#clear=46
#clear=47
#fcshdlc=48
#dacs=1-24:48
#dacsrbs=1-24:48
#
# Tone Zone Data
# ^^^^^^^^^^^^^^
# Finally, you can preload some tone zones, to prevent them from getting
# overwritten by other users (if you allow non-root users to open /dev/dahdi/*
# interfaces anyway.  Also this means they won't have to be loaded at runtime.
# The format is "loadzone=<zone>" where the zone is a two letter country code.
# 
# You may also specify a default zone with "defaultzone=<zone>" where zone
# is a two letter country code.
#
# An up-to-date list of the zones can be found in the file zonedata.c
#
loadzone = us
#loadzone = us-old
#loadzone=gr
#loadzone=it
#loadzone=fr
#loadzone=de
#loadzone=uk
#loadzone=fi
#loadzone=jp
#loadzone=sp
#loadzone=no
#loadzone=hu
#loadzone=lt
#loadzone=pl
defaultzone=us
#
# PCI Radio Interface
# ^^^^^^^^^^^^^^^^^^^
# (see http://www.zapatatelephony.org/app_rpt.html)
#
# The PCI Radio Interface card interfaces up to 4 two-way radios (either
# a base/mobile radio or repeater system) to DAHDI channels. The driver
# may work either independent of an application, or with it, through
# the driver;s ioctl() interface. This file gives you access to specify
# load-time parameters for Radio channels, so that the driver may run
# by itself, and just act like a generic DAHDI radio interface.
#
# Unlike the rest of this file, you specify a block of parameters, and
# then the channel(s) to which they apply. CTCSS is specified as a frequency
# in tenths of hertz, for example 131.8 HZ is specified as 1318. DCS
# for receive is specified as the code directly, for example 223. DCS for
# transmit is specified as D and then the code, for example D223.
#
# The hardware supports a "community" CTCSS decoder system that has
# arbitrary transmit CTCSS or DCS codes associated with them, unlike
# traditional "community" systems that encode the same tone they decode.
# 
# this example is a single tone DCS transmit and receive
#
# specify the transmit tone (in DCS mode this stays constant):
#tx=D371
#
# specify the receive DCS code:
#dcsrx=223
#
# this example is a "community" CTCSS (if you only want a single tone, then
# only specify 1 in the ctcss list)
#
# specify the default transmit tone (when not receiving):
#tx=1000
#
# Specify the receive freq, the tag (use 0 if none), and the transmit code.
# The tag may be used by applications to determine classification of tones.
# The tones are to be specified in order of presedence, most important first.
# Currently, 15 tones may be specified..
#
#ctcss=1318,1,1318
#ctcss=1862,1,1862
#
# The following parameters may be omitted if their default value is acceptible
#
# Set the receive debounce time in milliseconds:
#debouncetime=123
#
# set the transmit quiet dropoff burst time in milliseconds:
#bursttime=234
#
# set the COR level threshold (specified in tenths of millivolts)
# valid values are {3125,6250,9375,12500,15625,18750,21875,25000}
#corthresh=12500
#
# Invert COR signal {y,n}
#invertcor=y
# Set the external tone mode; yes, no, internal {y,n,i}
#exttone=y
#
# Now apply the configuration to the specified channels:
#
# We are all done with our channel parameters, so now we specify what
# channels they apply to
#channels=1-4
#
# Overiding PCM encoding
# ^^^^^^^^^^^^^^^^^^^^^^
# Usually the channel driver sets the encoding of the PCM for the
# channel (mulaw / alaw. That is: g711u or g711a). However there are
# some cases where you would like to override that. 'mulaw' and 'alaw'
# set different such encoding. Use them for channels you have already
# defined with e.g. 'bchan' or 'fxoks'.
#mulaw=1-4
#alaw=1-4
#
# 'deflaw' is similar, but resets the encoding to the channel driver's
# default. It must be useful for something, I guess.
#mulaw=1-10
#deflaw=5
#
# Echo Cancellers
# ^^^^^^^^^^^^^^^
# DAHDI uses modular echo cancellers that are configured per channel. The echo
# cancellers are compiled and installed as part of the dahdi-linux package.
# You can specify in this file the echo canceller to be used for each
# channel. The default behavior is for there to be NO echo canceller on any
# channel, so it is very important that you specify one here if you do
# not have hardware echo cancellers and need echo cancellation.
#
# Valid echo cancellers are: mg2, kb1, sec2, and sec.
# If compiled, 'hpec' is also a valid echo canceller.
# 
# To configure the default echo cancellers, use the format:
# echocanceller=<echocanceller name>,<channel(s)>
#
# Example:
# Configure channels 1 through 8 to use the mg2 echo canceller
#echocanceller=mg2,1-8 
#
# And change channel 2 to use the kb1 echo canceller.
#echocanceller=kb1,2
#