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Cisco 2900 Series and 3900 Series Hardware Installation Guide
OL-18712-02
Chapter 2 Preparing for Router Installation
Network Cabling Specifications
Serial DTE or DCE Devices
A device that communicates over a synchronous serial interface is either a DTE or DCE device. A DCE
device provides a clock signal that paces the communications between the device and the router. A DTE
device does not provide a clock signal. DTE devices usually connect to DCE devices. The documentation
that accompanied the device should indicate whether it is a DTE or DCE device. (Some devices have a
jumper to select either DTE or DCE mode.)
Table 2-1
lists typical DTE and DCE devices.
Signaling Standards Supported
The synchronous serial ports available for the router support the following signaling standards: they are
EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA-530. You can order a Cisco DB-60 shielded serial
transition cable that has the appropriate connector for the standard you specify. The documentation for
the device you want to connect should indicate the standard used for that device. The router end of the
shielded serial transition cable has 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 a connector appropriate
for the standard you specify.
The synchronous serial port can be configured as DTE or DCE, depending on the attached cable (except
EIA-530, which is DTE only).
All serial ports configured as DTE require external clocking from a CSU/DSU or other DCE device.
Although manufacturing your own serial cables is not recommended (because of the small size of the
pins on the DB-60 serial connector), cable pinouts are provided in the
Cisco Modular Access Router
Cable Specifications
document.
Distance Limitations
Serial signals can travel a limited distance at any given bit rate; generally, the slower the data rate, the
greater the distance. All serial signals are subject to distance limits, beyond which a signal significantly
degrades or is completely lost.
Note
Only the serial WAN interface card supports bit rates above 128 Kbps.
Table 2-2
lists the recommended maximum speeds and distances for each serial interface type; however,
you might get good results at speeds and distances greater than those listed, if you understand the
electrical problems that might arise and can compensate for them. For instance, the recommended
maximum rate for V.35 is 2 Mb/s, but 4 Mb/s is commonly used.
Table 2-1
Typical DTE and DCE Devices
Device Type
Gender
Typical Devices
DTE
Male
1
1.
If pins protrude from the base of the connector, the connector is male.
Terminal
PC
DCE
Female
2
2.
If the connector has holes to accept pins, the connector is female.
Modem
CSU/DSU
Multiplexer
