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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">3</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">Serial Point-to-Point Links</font></strong></td>
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<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">3.1.4</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">DTE-DCE</font></strong></td>
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<font face="Arial" size="2">A serial connection has a data terminal
equipment (DTE) device at one end of the connection and a data
communications equipment (DCE) device at the other end. The connection
between the two DCEs is the WAN service provider transmission network. The CPE, which is generally a router, is the DTE.
Other DTE examples could be a terminal, computer, printer, or fax
machine. The DCE, commonly a modem or CSU/DSU, is the device used to
convert the user data from the DTE into a form acceptable to the WAN
service provider transmission link. This signal is received at the
remote DCE, which decodes the signal back into a sequence of bits.
This sequence is then signaled to the remote DTE.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font><p>
<font face="Arial" size="2">Many standards have been developed to
allow DTEs to communicate with DCEs. The Electronics Industry
Association (EIA) and the International
Telecommunication Union Telecommunications Standardization Sector (ITU-T) have been most active
in the development of these standards.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"></font></p>
<p><font face="Arial" size="2">The DTE-DCE interface for a particular
standard defines the following specifications:</font></p>
<ul>
<li><font face="Arial" size="2"><b>Mechanical/physical</b> � Number
of pins and connector type</font></li>
<li><font face="Arial" size="2"><b>Electrical</b> � Defines voltage
levels for 0 and 1</font></li>
<li><font face="Arial" size="2"><b>Functional</b> � Specifies the
functions that are performed by assigning meanings to each of the
signaling lines in the interface</font></li>
<li><font face="Arial" size="2"><b>Procedural</b> � Specifies the
sequence of events for transmitting data</font></li>
</ul>
<p><font face="Arial" size="2">If two DTEs must be connected together,
like two computers or two routers in the lab, a special cable called a
null-modem is necessary to eliminate the need for a DCE. For
synchronous connections, where a clock signal is needed, either an
external device or one of the DTEs must generate the clock signal.</font></p>
<p><font face="Arial" size="2">The synchronous serial port on a router
is configured as DTE or DCE depending on the attached cable, which is
ordered as either DTE or DCE to match the router configuration. If the
port is configured as DTE, which is the default setting, external
clocking is required from the CSU/DSU or other DCE device.</font></p>
<p><font face="Arial" size="2">The cable for the DTE to DCE connection
is a shielded serial transition cable. The router end of the shielded
serial transition cable may be a DB-60 connector, which connects to
the DB-60 port on a serial WAN interface card. The other end of the
serial transition cable is available with the connector appropriate
for the standard that is to be used. The WAN provider or the CSU/DSU
usually dictates this cable type. Cisco devices support the EIA/TIA-232,
EIA/TIA-449, V.35, X.21, and EIA/TIA-530 serial standards.</font></p>
<p><font face="Arial" size="2">To support higher densities in a
smaller form factor, Cisco has introduced a smart serial cable. The
serial end of the smart serial cable is a 26-pin connector
significantly more compact than the DB-60 connector.</font> </p>
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Interactive Media Activity</a></b></font></p>
</font><font FACE="Arial" SIZE="2" COLOR="#808080">
<p>PhotoZoom: DCE/DTE Cable</p>
<p>In this
PhotoZoom, the student will view DCE and DTE cable.</p>
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<p><font color="#808080">
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<b>Web Links</b></font></p>
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<p>High-Speed Serial Interface (HSSI)<p>
<a target="_blank" href="http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/hssi.htm">
http://www.cisco.com/univercd/cc/
td/doc/ cisintwk/ito_doc/ hssi.htm</a></font></p>
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