2-8
Cisco Connected Grid Routers 2010 Hardware Installation Guide
OL-21559-01
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 DCE or DTE 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.)
lists typical DTE and DCE devices.
Signaling Standards Supported
The synchronous serial ports available for the router support the following signaling standards:
EIA/TIA-232 (EIA-323). You can order a Cisco DB-25 shielded serial transition cable that has the
appropriate connector for the standard you specify. The documentation for the device should indicate the
standard used for that device. The router end of the shielded serial transition cable has a DB-25
connector, which connects to the DB-25 port on a serial grid router 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.
All serial ports configured as DTE require external clocking from a CSU/DSU or other DCE device.
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.
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
Table 2-2
Serial Signal Transmission Speeds and Distances
Distance for
EIA/TIA-232
Distance for X.21 and
V.35
Distance for USB
Rate (bps)
Feet
Meters
Feet
Meters
Feet
Meters
2400
200
60
4100
1250
16.4
5
4800
100
30
2050
625
16.4
5
9600
50
15
1025
312
16.4
5
