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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">4</font></b><font face="Arial" size="2" color="#FFFFFF"><b>.1</b></font></td>
<td bgcolor="#336666"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
<td bgcolor="#336666" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">ISDN Concepts</font></strong></td>
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<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">4.1.6</font></b></td>
<td bgcolor="#669999"><img border="0" src="../../images/transdot.gif" width="10" height="1"></td>
<td bgcolor="#669999" height="25" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">Determining the router ISDN
interface</font></strong></td>
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<font face="Arial" size="2">In the United States, the customer is
required to provide the NT1. In Europe and various other countries,
the telephone company provides the NT1 function and presents an S/T
interface to the customer. In these configurations, the customer is
not required to supply a separate NT1 device or integrated NT1
function in the terminal device. Equipment such as router ISDN modules
and interfaces must be ordered accordingly.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><p>
<font face="Arial" size="2">To select a Cisco router with the appropriate ISDN interface, do the
following:</p>
<ol>
<li>Determine whether the router supports ISDN BRI. Look on the back of
the router for a BRI connector or a BRI WAN Interface Card (WIC).</li>
<li>Determine the provider of the NT1. An NT1 terminates the local loop
to the central office (CO) of the ISDN service provider. In the United
States, the NT1 is Customer Premise Equipment (CPE), meaning that it
is the responsibility of the customer. In Europe, the service provider
typically supplies the NT1.
</li>
<li>If the NT1 is CPE, make sure the router has a U interface. If the
router has an S/T interface, then it will need an external NT1 to
connect to the ISDN provider.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></li>
</ol>
<p>
<font face="Arial" size="2">If the router has a connector labeled BRI then it is already
ISDN-enabled. With a native ISDN interface already built in, the
router is a TE1. If the router has a U interface, it also has a
built-in NT1.
<img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12"></font></p>
<p>
<font face="Arial" size="2">If the router does not have a connector labeled BRI, and it is a
fixed-configuration, or non-modular router, then it must use an
existing serial interface. With non-native ISDN interfaces such as
serial interfaces, an external TA device must be
attached to the serial interface to provide BRI connectivity. If the
router is modular it may be possible to upgrade to a native ISDN
interface, providing it has an available slot.</font></p>
<blockquote>
<p>
<font face="Arial" size="2"><b>Caution: </b>A router with a U interface should never be connected to an
NT1 as it will damage the interface.</font></p>
</blockquote>
<p>
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<TD><IMG alt="" height="1" width="3" src="../../images/s.gif"></TD><TD align="right" valign="top">
<IMG alt="" src="../../images/corner_ur_7.gif" width="7" height="7"></TD>
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<p><font color="#808080">
<img border="0" src="../../images/links_icon.gif" width="25" height="25">
<b>Web Links</b></font></p>
</font><font FACE="Arial" SIZE="2" COLOR="#808080">
<p>Integrated Services Digital Network (ISDN)<p>
<a target="_blank" href="http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/isdn.htm">
http://www.cisco.com/univercd/cc/
td/doc/ cisintwk/ito_doc/ isdn.htm</a></font></p>
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