<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>FXO and FXS Channels</title><link rel="stylesheet" href="styles.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /><link rel="start" href="index.html" title="Asterisk™: The Future of Telephony" /><link rel="up" href="asterisk-CHP-4.html" title="Chapter 4. Initial Configuration of Asterisk" /><link rel="prev" href="setting_up_dialplan.html" title="Setting Up the Dialplan for Some Test Calls" /><link rel="next" href="asterisk-CHP-4-SECT-5.html" title="Configuring an FXO Channel for a PSTN Connection" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">FXO and FXS Channels</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="setting_up_dialplan.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Initial Configuration of Asterisk</th><td width="20%" align="right"> <a accesskey="n" href="asterisk-CHP-4-SECT-5.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="asterisk-CHP-4-SECT-4"></a>FXO and FXS Channels</h2></div></div></div><p>The difference<a id="I_indexterm4_tt451" class="indexterm"></a><a id="I_indexterm4_tt452" class="indexterm"></a> between an FXO channel and an FXS channel is simply which
end of the connection provides the dial tone. An FXO port does not
generate a dial tone; it accepts one. A common example is the dial tone
provided by your phone company. An FXS port provides both the dial tone
and ringing voltage to alert the station user of an inbound call. Both
interfaces provide bidirectional communication<a id="I_indexterm4_tt453" class="indexterm"></a><a id="I_indexterm4_tt454" class="indexterm"></a><a id="I_indexterm4_tt455" class="indexterm"></a> (i.e., communication that is transmitted and received in
both directions simultaneously).<sup>[<a id="id4116436" href="#ftn.id4116436">52</a>]</sup></p><p>If your Asterisk server has a compatible FXO port, you can plug a
telephone line from your <a id="I_indexterm4_tt456" class="indexterm"></a>telephone company (or “telco”) into this port. Asterisk can
then use the telco line to place and receive telephone calls. By the same
token, if your Asterisk server has a compatible FXS port, you may plug an
analog telephone into your Asterisk server, so that Asterisk may call the
phone and you may place calls.</p><p>Ports<a id="I_indexterm4_tt457" class="indexterm"></a> are defined in the configuration by the signaling they use,
as opposed to the physical type of port they are. For instance, a physical
FXO port will be defined in the configuration with FXS signaling, and an
FXS port will be defined with FXO signaling. This can be confusing until
you understand the reasons for it. FX_ cards are named not according to
what they are, but rather according to what is connected to them. An
FX<span class="emphasis"><em>S</em></span> card, therefore, is a card that connects to a
<span class="emphasis"><em>s</em></span>tation. Since that is so, you can see that in order
to do its job, an FXS card must <span class="emphasis"><em>behave</em></span> like a central
office and use FXO signaling. Similarly, an FX<span class="emphasis"><em>O</em></span> card
connects to a central <span class="emphasis"><em>o</em></span>ffice (CO), which means it
will need to behave like a station and use FXS signaling. The modem in
your computer is a classic example of an FXO device.</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>The older <a id="I_indexterm4_tt458" class="indexterm"></a><a id="I_indexterm4_tt459" class="indexterm"></a>Digium<a id="I_indexterm4_tt460" class="indexterm"></a> X100P card used a Motorola chipset, and the X101P (which
Digium sold before completely switching to the TDM400P) is based on the
Ambient/Intel MD3200 chipset. These cards are modems with drivers
adapted to utilize the card as a single FXO device (the telephone
interface cannot be used as an FXS port). Support for the X101P card has
been dropped in favor of the TDM series of cards.</p><p>These cards (or their clones) <span class="bold"><strong>SHOULD
NOT</strong></span> be used in production environments. They are $10 on eBay
for a reason.</p><p>The X100P/X101P cards are poor cards for production use due to
their tendency to introduce echo into your telephone calls, and their
lack of remote disconnect supervision. Do yourself a favor and don’t
waste your time with this hardware. You will find that if you ask the
community for support of these cards, many responses will be hostile.
You have been warned.</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="asterisk-CHP-4-SECT-4.1"></a>Determining the FXO and FXS Ports on Your TDM400P</h3></div></div></div><p><a href="asterisk-CHP-4-SECT-4.html#asterisk-CHP-4-FIG-1" title="Figure 4.1. A TDM400P with an FXS module (1 across) and an FXO module (2 across)">Figure 4.1, “A TDM400P with an FXS module (1 across) and an FXO module (2
across)”</a> contains a picture of a
TDM400P with an FXS<a id="I_indexterm4_tt461" class="indexterm"></a> module and an FXO module. You can’t see the colors, but
module 1 is a green FXS module, and module 2 is an orange-red FXO
module. In the bottom-right corner of the picture is the Molex
connector, where power is supplied from the computer’s power
supply.</p><div class="figure"><a id="asterisk-CHP-4-FIG-1"></a><p class="title"><b>Figure 4.1. A TDM400P with an FXS module (1 across) and an FXO module (2
across)</b></p><div class="mediaobject"><a id="I_mediaobject4_tt462"></a><img src="figs/web/ast2_0401.png" alt="A TDM400P with an FXS module (1 across) and an FXO module (2 across)" /></div></div><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title"><a id="asterisk-CHP-4-NOTE-20"></a>Warning</h3><p>Plugging an FXS port (the green module) into the PSTN may
destroy the module and the card due to voltage being introduced into a
system that wants to produce voltage, not receive it!</p></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title"><a id="asterisk-CHP-4-NOTE-21"></a>Tip</h3><p>Be sure to connect your computer’s power supply to the
<a id="I_indexterm4_tt463" class="indexterm"></a>Molex connector on the TDM400P if you have FXS modules,
as it is used to supply the voltage needed to drive the ring generator
on the FXS ports. The Molex connector is not required if you have only
FXO modules.</p></div></div><div class="footnotes"><br /><hr width="100" align="left" /><div class="footnote"><p><sup>[<a id="ftn.id4116436" href="#id4116436">52</a>] </sup>Bidirectional communication is also known as <span class="emphasis"><em>full
duplex</em></span> in some circles. <span class="emphasis"><em>Half duplex</em></span>
means communication is only traveling in one direction at a
time.</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="setting_up_dialplan.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="asterisk-CHP-4.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="asterisk-CHP-4-SECT-5.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Setting Up the Dialplan for Some Test Calls </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Configuring an FXO Channel for a PSTN Connection</td></tr></table></div><div xmlns="" id="svn-footer"><hr /><p>You are reading <em>Asterisk: The Future of Telephony</em> (2nd Edition for Asterisk 1.4), by Jim van Meggelen, Jared Smith, and Leif Madsen.<br />
This work is licensed under the <a href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Attribution-Noncommercial-No Derivative Works License v3.0</a>.<br />
To submit comments, corrections, or other contributions to the text, please visit <a href="http://oreilly.com/catalog/9780596510480/">http://www.oreilly.com/</a>.</p></div></body></html>
distrib
>
Mandriva
>
2008.1
>
i586
>
media
>
contrib-updates
>
by-pkgid
>
c7095aefea7b97fbd2a596dcbfb9d481
>
files
>
446
