Serial Connections - Cisco EF4116 Hardware Installation And Maintenance Manual

Serial Connections

When setting up your router, consider distance limitations and potential electromagnetic
interference (EMI) as defined in the Electronic Industries Association's (EIA) and
Telecommunications Industry Association (TIA) standards, such as EIA/TIA-232.
Serial Line Distance Limitations
Serial signals can travel a limited distance at any given bit rate; generally, the slower the baud rate,
the greater the distance. All serial signals are subject to distance limits, beyond which a signal
degrades significantly or is completely lost. Table 2-4 lists the IEEE-recommended maximum
speeds and distances for each serial interface type; however, 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. If you understand the electrical problems that might arise
and can compensate for them, you can get good results with rates and distances greater than those
shown. However, do so at your own risk.
Table 2-4
EIA/TIA-232
Distance
Rate (bps)
2400
4800
9600
19200
38400
56000
1544000 (T1)
Balanced drivers allow EIA/TIA-449 signals to travel greater distances than EIA/TIA-232. The
recommended distance limits for EIA/TIA-449 shown in Table 2-4 are also valid for V.35, X.21, and
EIA-530. However, you can get good results at distances and rates greater than those shown in
Table 2-4. Typically, EIA/TIA-449 and EIA-530 support 2-Mbps rates, and V.35 can support
4-Mbps rates.
EIA/TIA-232 Connections
EIA/TIA-232, the most common interface standard in the United States, supports unbalanced
circuits at signal speeds up to 64 Kbps. The network end of the adapter cable is a standard 25-pin
D-shell connector known as a DB-25. (See Figure 2-13.) The router Console and Auxiliary ports
also use EIA/TIA-232 connections; however, the serial module ports support synchronous
connections, and the console and auxiliary ports support asynchronous connections.
IEEE Standard Transmission Speeds and Distances
EIA/TIA-449, X.21, V.35,
EIA-530 Distance
Feet Meters Feet
200 60 4100
100 30 2050
50 15 1025
25 7.6 513
12 3.7 256
8.6 2.6 102
N/A N/A 50
Network Connection Considerations
Meters
1250
625
312
156
78
31
15
Preparing for Installation 2-15