Connecting Serial Network Modules to a Network 6-3
Distance Limitations
The synchronous serial port can be configured as DTE or DCE (except EIA-530, which is
DTE only), depending on the attached cable. To order a shielded cable, contact customer
service. (See the Cisco Information Packet publication that came with your router.)
Note 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 online
document Cisco Modular Access Router Cable Specifications. This document is located on
the Documentation CD-ROM that accompanied your router, and on Cisco Connection
Online.
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 degrades significantly or is completely lost.
Table 6-2 lists the recommended maximum speeds and distances for each serial interface
type; however, if you understand potential electrical problems and compensate for them,
you may get good results at speeds and distances greater than those listed. For instance, the
recommended maximum rate for V.35 is 2 Mbps, but 4 Mbps is commonly used.
Table 6-2 Serial Interace Speeds and Distances
EIA/TIA-232
Distance
EIA/TIA-449, X.21, V.35, EIA-530
Distance
Rate (bps) Feet Meters Feet Meters
2400 200 60 4100 1250
4800 100 30 2050 625
9600 50 15 1025 312
19200 25 7.6 513 156
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