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Zapata Telephony Interface Driver

Zaptel is a short for ZAPata TELephony.

1. Supported Hardware

1.1. Digital Cards

1.2. Analog Cards

1.3. Other Drivers

2. Build Requirements

You will need a matching kernel source tree and a working Linux build system. Some of the programs require some additional libraries.

The script install_prereq should help you install the required packages. To see what it suggests, run:

./install_prereq test

You can either copy/paste that code to a terminal to run it, or just run:

./install_prereq install

2.1. Kernel Source / "Headers"

2.2. Kernel Configuration

If you build a custom kernel, note the following configuration items:

2.3. Build System

gcc and friends. Generally you will need to install the package gcc. There may be cases where you will need a specific version of gcc to build kernel modules.

2.4. Extra Libraries

Some libraries are needed for extra utilities that are provided with Zaptel

2.5. Distribution-Specific Instructions

2.5.1. Debian 4.0 (Etch)

apt-get install linux-headers-`uname -r` build-essential libnewt-dev libusb-dev

2.5.2. Debian 3.1 (Sarge)

apt-get install kernel-headers-`uname -r` build-essential libnewt-dev libusb-dev

2.5.3. RHEL4 / CentOS 4

You need the following non-kernel-related packages:

yum install gcc newt-devel libusb-devel

If the following command produces an error, you need to install the kernel devel package:

ls /lib/modules/`uname -r`/build/.config

The right one depends on your kernel version. If the following command produces output you have an SMP kernel:

uname -r | grep smp

and thus need to run:

yum install kernel-smp kernel-smp-devel

If that command produced no output, you have a non-SMP kernel:

yum install kernel kernel-devel

At this point you should probably reboot to get the new kernel in effect.

3. Installation

Note: If using sudo to build/install, you may need to add /sbin to your PATH.

# optional step: select custom configuration:
#make menuconfig
make install
# To install init scripts and config files:
#make config

3.1. Build Tweaks

3.1.1. Selecting Modules and Utilities

You can select the modules and utilities you wish to build and firmwares you wish to download by running make menuselect . The selection of modules that you build (or rather: not build) is saved in the file menuselect.makeopts.

3.1.2. Extra Modules

To build extra modules / modules directory not included in the Zaptel distribution, use the optional variables MODULES_EXTRA and SUBDIRS_EXTRA:

make MODULES_EXTRA="mod1 mod2"
make MODULES_EXTRA="mod1 mod2" SUBDIRS_EXTRA="subdir1/ subdir1/"

Note that those names are not guaranteed to continue to work on newer versions. Hopefully there will be no need for such extra configuration.

3.1.3. Partial Build/Install

There are some make targets that are provided to build or install just parts of Zaptel:

  1. Build targets:

    • make modules: build just the kernel modules.

    • make programs: Build just the Zaptel userspace programs. partial targets of it:

      • make utilname: builds utilname alone (e.g: make ztdiag)

      • make utils: Build libtonezone.

      • make libs: Build libtonezone.

  2. Install targets:

    • make install-modules: install just kernel modules.

    • make firmware: download and install firmwares for Digium cards

    • make install-programs: Userspace: Partial targets of it are:

      • make install-utils: install Zaptel userspace programs and and basic support files.

      • make install-libs: install libtonezone

      • make install-include: install zaptel.h

    • make config: should be run once to configure

3.1.4. Building to a Subtree

The following may be useful when testing the package or when preparing a package for a binary distribution (such as an rpm package) installing onto a subtree rather than on th real system.

make install DESTDIR=targetdir

This can be useful for any partial install target of the above (e.g: install-modules or install-programs).

the targetdir must be an absolute path, at least if you install the modules. To install to a relative path you can use something like:

make install-modules DESTDIR=$PWD/target

The install target might fail if run as a user to a DESTDIR when attempting to generate device files. In that case, try:

make install DESTDIR=$PWD/target DYNFS=

3.1.5. Test Install: live_zap

If you need to test a version of Zaptel without touching the version installed on your system, you can use the script live_zap . Note, however, that it may take some extra configuration to be used right.

Basic usage:

./live_zap install # instead of 'make install'
./live_zap config  # instead of 'make config'
./live_zap unload  # instead of '/etc/init.d/zaptel stop'
./live_zap load    # instead of '/etc/init.d/zaptel start'

Everything is installed under the subdirectory live/ . You will probably need to adjust MODULES . Generally you should not edit the script itself, but , rather, edit live/live.conf . Please let me know if you needed to change anything in the script beyond changing live.conf so I can include useful fixes.

Testing on a different machine:

./live_zap install # instead of 'make install'
./live_zap config  # instead of 'make config'
./live_zap rsync root@remotehost
ssh root@remotehost
# in the remote host:
cd /tmp
./live_zap unload
./live_zap load

live_zap also has a command called "exec" to execute commands from the installed environment. e.g.:

./live_zap exec lszaptel

This sets PATH, PERL5LIB (for the Zaptel-perl modules) and some other settings.

For Xorcom Astribank you may need to load a different version of firmware from that installed on the system. In this case, start with editing the real system's /etc/default/zaptel (on Debian) or /etc/sysconfig/zaptel (on RedHat/SUSE) and set:


and then run:

./live_zap unload
./live_zap exec ./live/usr/share/zaptel/xpp_fxloader reset
./live_zap exec ./live/usr/share/zaptel/xpp_fxloader load
# wait a few seconds, see the output of lsusb
./live_zap load

3.1.6. ./configure Options

The configure script various several tests and based on them generates some files ( build_tools/menuselect-deps and makeopts). You can pass it —with options and variable settings, for instance:

./configure --without-ncurses CC="gcc-4.10"

If you just want to recreate the same files without a full detection run, use:


To re-run ./configure with the same parameters it was run with last time, use:

./ocnfig.status --recheck

4. Configuration

4.1. zaptel.conf

The main method to configure Zaptel devices is using the utility ztcfg. ztcfg reads data from the configuration file /etc/zaptel.conf , figures out what configuration to send to channels, and send it.

A sample annotated zaptel.conf is included in this directory and installed by default to /etc/zaptel.conf . Edit it to suit your configuration. Alternatively use the script genzaptelconf to generate one that should work with your system.

4.2. sysconfig/default

The configuration file of the zaptel init.d script is either /etc/default/zaptel (Debian systems) or /etc/sysconfig/zaptel (most others). That file is used to override defaults that are set at the beginning of the init.d script.

For instance, to define for the init.d script to load the modules wctdm and xpp_usb (in that order) add the following line to that file:

MODULES="wctdm xpp_usb"

Currently that file must set "TELEPHONY=yes" for the zaptel init.d to work.

4.3. Module Parameters

The kernel modules can be configured through module parameters. Module parameters can optionally be set at load time. They are normally set (if needed) by a line in a file under /etc/modprobe.d/ or in the file /etc/modprobe.conf (Or /etc/modules.conf in kernel 2.4).

Example line:

options zaptel debug=1

The module parameters can normally be modified at runtime through sysfs:

pungenday:~# cat /sys/module/zaptel/parameters/debug
pungenday:~# echo 1 >/sys/module/zaptel/parameters/debug
pungenday:~# cat /sys/module/zaptel/parameters/debug

Viewing and setting parameters that way is possible as of kernel 2.6 . In kernels older than 2.6.10, the sysfs "files" for the parameters reside directly under /sys/module/module_name .

Useful module parameters:

debug (most modules)

Sets debug mode / debug level. With most modules debug can be either disabled (0, the default value) or enabled (any other value). wctdm and wcte1xp print several extra debugging messages if the value of debug is more than 1. Some modules have "debugging flags" bits - the value of debug is a bitmask and several messages are printed if some bits are set:

  • ztdummy:

    • 1: DEBUG_GENERAL - general error messages.

    • 2: DEBUG_TICKS - Show that the module is alive :-)

  • wctdm24xxp:

    • 1: DEBUG_CARD


  • wct4xxp:

    • 1: DEBUG_MAIN

    • 2: DEBUG_DTMF

    • 4: DEBUG_REGS

    • 8: DEBUG_TSI


    • 32: DEBUG_RBS

    • 64: DEBUG_FRAMER

  • xpp: Previously (before 1.2.26 / 1.4.11) it was called "print_dbg". See also README.Astribank:

    • 1: GENERAL - General debug comments.

    • 2: PCM - PCM-related messages. Tend to flood logs.

    • 4: LEDS - Anything related to the LEDs status control. The driver produces a lot of messages when the option is enabled.

    • 8: SYNC - Synchronization related messages.

    • 16: SIGNAL - Zaptel signalling related messages.

    • 32: PROC - Messages related to the procfs interface.

    • 64: REGS - Reading and writing to chip registers. Tends to flood logs.

    • 128: DEVICES - Device instantiation, destruction and such.

    • 256 - COMMANDS - Protocol commands. Tends to flood logs.

deftaps (zaptel)

The default size for the echo canceller. The number is in "taps", that is "samples", 1/8 ms. The default is 64 - for a tail size of 8 ms. Asterisk's chan_zap tends to pass its own value anyway, with a different default size. So normally setting this doesn't change anything.

To get a list of parameters supported by a module, use

modinfo module_name

Or, for a module you have just built:

modinfo ./module_name.ko

For the xpp modules this will also include the description and default value of the module. You can find a list of useful xpp module parameters in README.Astribank .

5. Reference Configuration

Zaptel Configuration File

This file is parsed by the Zaptel Configurator, ztcfg

5.1. 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 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 is used as the master source of clock timing. If it is, our own clock will synchronise to it. T1/E1's 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 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. 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)

one of d4 or esf for T1 or cas or ccs for E1 and BRI. d4 could be referred to as sf or superframe


one of ami or b8zs for T1 or ami or hdb3 for E1 and 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.


5.2. Dynamic Spans

Next come the dynamic span definitions, in the form:


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 zaptel device if you are not using external timing.


If a non-zero timing value is used, as above, only the last span should have the non-zero value.

5.3. Channel Configuration

Next come the definitions for using the channels. The format is: <device>=<channel list>

Valid devices are:


Channel(s) are signalled using E&M signalling (specific implementation, such as Immediate, Wink, or Feature Group D are handled by the userspace library).


Channel(s) are signalled using FXS Loopstart protocol.


Channel(s) are signalled using FXS Groundstart protocol.


Channel(s) are signalled using FXS Koolstart protocol.


Channel(s) are signalled using FXO Loopstart protocol.


Channel(s) are signalled using FXO Groundstart protocol.


Channel(s) are signalled using FXO Koolstart protocol.


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.

No signalling is performed, each channel in the list remains idle


Channel(s) are bundled into a single span. No conversion or signalling is performed, and raw data is available on the master.


Like clear except all channels are treated individually and are not bundled. inclear is an alias for this.


The zaptel driver performs HDLC encoding and decoding on the bundle, and the resulting data is communicated via the master device.


The zaptel 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.


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.


The zaptel 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.

The zaptel driver cross connects the channels starting at the channel number listed at the end, after a colon


The zaptel 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:


5.4. 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/zap/* 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 zaptel/zonedata.c

loadzone = us
#loadzone = us-old

5.5. PCI Radio Interface


The PCI Radio Interface card interfaces up to 4 two-way radios (either a base/mobile radio or repeater system) to Zaptel 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 Zaptel 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):


specify the receive DCS code:


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):


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..


The following parameters may be omitted if their default value is acceptible

Set the receive debounce time in milliseconds:


set the transmit quiet dropoff burst time in milliseconds:


set the COR level threshold (specified in tenths of millivolts) valid values are {3125,6250,9375,12500,15625,18750,21875,25000}


Invert COR signal {y,n}


Set the external tone mode; yes, no, internal {y,n,i}


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


5.6. 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.


deflaw is similar, but resets the encoding to the channel driver's default. It must be useful for something, I guess.


5.7. Tonezones

The file zonedata.c contains the information about the tone zones used in libtonezone (and hence also in ztcfg). Here is a list of those zones:

6. Zaptel PERL modules

The directory xpp/utils has, in addition to helper utilities for the Xorcom Astribank, a collection of perl modules to provide information related to Zaptel. The perl modules themselves are under xpp/utils/zconf . In xpp/utils there are several utilities that use those modules: - xpp-specific: zt_registration, xpp_sync, xpp_blink . - General: lszaptel, zapconf, zaptel_hardware

The zaptel perl modules will currently only be automatically installed if you happen to isntall the xpp module. This should be the defualt, but you can also initiate it manually by running:

make -C xpp/utils install

Those utilities require the perl modules to be installed, however they will also look for them in the directory zconf, and thus can be run directly from the zaptel source tree. For example:


To get usage information on a program, you can also use perldoc (sometimes provided in a package separate from perl itself). For instance:

perldoc ./xpp/utils/lszaptel

Some of them are specific for the Xorcom Astribank and described in its docuemntation. the others are:


A somewhat glorified cat /proc/zaptel/*.


An currently experimental and intended to eventually replace genzaptelconf by a more maintainable code.


A two-liner script (not installed by default) that simply returns the modules that should be modprobed on this system.


Uses the information from sysfs and its own knowledge to show what PCI/USB Zaptel hardware is connected and if it is currently used by a driver. Shows also some more information for Astrobanks from /proc/xpp .

7. Internals

7.1. Zaptel Device Files

Userspace programs will usually interact with Zaptel through device files under the /dev/zap directory (pedantically: characted device files with major number 196) . Those device files can be generated statically or dynamically through the udev system.

7.2. Zaptel Timing

A PBX system should generally have a single clock. If you are connected to a telephony provider via a digital interface (e.g: E1, T1) you should also typically use the provider's clock (as you get through the interface). Hence one important job of Asterisk is to provide timing to the PBX.

Zaptel "ticks" once per millisecond (1000 times per second). On each tick every active zaptel channel reads and 8 bytes of data. Asterisk also uses this for timing, through a zaptel pseudo channel it opens.

However, not all PBX systems are connected to a telephony provider via a T1 or similar connection. With an analog connection you are not synced to the other party. And some systems don't have Zaptel hardware at all. Even a digital card may be used for other uses or is simply not connected to a provider. Zaptel cards are also capable of providing timing from a clock on card. Cheap x100P clone cards are sometimes used for that pupose.

If all the above fail, you can use the module ztdummy to provide timing alone without needing any zaptel hardware. It will work with most systems and kernels.

You can check the zaptel timing source with zttest, which is a small utility that is included with zaptel. It runs in cycles. In each such cycle it tries to read 8192 bytes, and sees how long it takes. If zaptel is not loaded or you don't have the device files, it will fail immedietly. If you lack a timing device it will hang forever in the first cycle. Eitherwise it will just give you in each cycle the percent of how close it was. Also try running it with the option -v for a verbose output.

To check the clock source that is built into ztdummy, you can either look at title of its span in /proc/zaptel file for a "source:" in the description. Or even run:

strings zaptel.ko | grep source:

7.3. Spans and Channels

Zaptel provides telephony channels to the userspace applications. Those channels are channels are incoreperated into logical units called spans.

With digital telephony adapters (e.g: E1 or T1), a span normally represents a single port. With analog telephony a span typically represents a PCI adapter or a similar logical unit.

Both channels and spans are identified by enumerating numbers (beginning with 1). The number of the channel is the lowest unused one when it is generated, and ditto for spans.

See also the span configuration directive.

7.4. PROCFS Interface: /proc/zaptel

A simple way to get the current list of spans and channels each span contains is the files under /proc/zaptel . /proc/zaptel is generated by zaptel as it loads. As each span registers to Zaptel, a file under /proc/zaptel is created for it. The name of that file is the number of that span.

Each file has a 1-line title for the span followed by an empty line and then a line for each channel of the span.

The title line shows the number of the span, its name and title, and (potentially) the alarms in which it is.

The title shows the span number and name, followed by any allarms the span may have: For example, here is the first span in my system (with no alarms):

Span 1: XBUS-00/XPD-00 "Xorcom XPD #0/0: FXS"

The channel line for each channel shows its channel number, name and the actual signalling assigned to it through ztcfg. Before being configured by ztcfg: This is Zaptel channel 2, whose name is XPP_FXS/0/0/1.

2 XPP_FXS/0/0/1

After being configured by ztcfg: the signalling FXOLS was added. FXS channels have FXO signalling and vice versa:


If the channel is in use (typically opened by Asterisk) then you will see an extra (In use):

2 XPP_FXS/0/0/1 FXOLS (In use)

7.5. ABI Compatibility

Like any other kernel code, Zaptel strives to maintain a stable interface to userspace programs. The API of Zaptel to userspace programs, zaptel.h, has remained backword-compatible for a long time and is expected to remain so in the future. With the ABI (the bits themselves) things are slightly trickier.

Zaptel's interface to userspace is mostly ioctl(3) calls. Ioctl calls are identified by a number that stems from various things, one of which is the size of the data structure passed between the kernel and userspace.

Many of the Zaptel ioctl-s use some sepcific structs to pass information between kernel and userspace. In some cases the need arose to pass a few more data members in each call. Simply adding a new member to the struct would have meant a new number for the ioctl, as its number depends on the size of the data passed.

Thus we would add a new ioctl with the same base number and with the original struct.

So suppose we had the following ioctl:

struct zt_example {
        int sample;

#define ZT_EXAMPLE     _IOWR (ZT_CODE, 62, struct zt_example)

And we want to add the field int onemore, we won't just add it to the struct. We will do something that is more complex:

/* The original, unchanged: */
struct zt_example_v1 {
        int sample;

/* The new struct: */
struct zt_example {
        int sample;
        int onemore;

#define ZT_EXAMPLE_V1  _IOWR (ZT_CODE, 62, struct zt_example_v1)
#define ZT_EXAMPLE     _IOWR (ZT_CODE, 62, struct zt_example)

We actually have here two different ioctls: the old ZT_EXAMPLE would be 0xC0044A3E . ZT_EXAMPLE_V1 would have the same value. But the new value of ZT_EXAMPLE would be 0xC0084A3E .

Programs built with the original zaptel.h (before the change) use the original ioctl, whether or not the kerenl code is actually of the newer version. Thus in most cases there are no compatibility issues.

When can we have compatibility issues? if we have code built with the new zaptel.h, but the loaded kernel code (modules) are of the older version. Thus the userspace program will try to use the newer ZT_EXAMPLE (0xC0084A3E). But the kernel code has no handler for that ioctl. The result: the error 25, ENOTTY, which means "Inappropriate ioctl for device".

As a by-product of that method, for each interface change a new #define is added. That definition is for the old version and thus it might appear slightly confusing in the code, but it is useful for writing code that works with both versions of Zaptel.

7.5.1. Past Incompatibilities

Zaptel 1.4.10:
Zaptel 1.4.8:
Zaptel 1.4.6:

ZT_SPANINFO_V1 was originally called (up to zaptel 1.4.8) "ZT_SPANINFO_COMPAT".

8. PPP Support

Zaptel digital cards can provide data channels through ppp as point-to-point connections. This requires a plugin to the ppp daemon that is included in the ppp/ subdirectory. To install it:

  1. Make sure you have the PPP source / headers installed. On Debian:

    apt-get install ppp-dev
  2. Run make on the ppp subdirectory:

    make -C ppp
    make -C ppp install
  3. Make sure your kernel has support for both PPP (which is common is distribution kernels and for HDLC (much less common) - CONFIG_PPP and CONFIG_HDLC .

9. License

This package is distributed under the terms of the GNU General Public License Version 2, except for some components which are distributed under the terms of the GNU Lesser General Public License Version 2.1. Both licenses are included in this directory, and each file is clearly marked as to which license applies.

If you wish to use the Zaptel drivers in an application for which the license terms are not appropriate (e.g. a proprietary embedded system), licenses under more flexible terms can be readily obtained through Digium, Inc. at reasonable cost.

10. How do I report bugs or contribute?

Please report bug and patches to the bug tracker at in the "Zaptel" category.

11. Does anything use this library so far?

Yes, the Asterisk Open Source PBX does.