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48 VIP-4R/4T Installation and Configuration
VIP Port Adapter Functions
Serial 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 8 lists the IEEE-recommended maximum speeds
and distances for each 4T port adapter serial interface type. The recommended maximum rate for
V.35 is 2.048 Mbps.
Table 8 IEEE Standard EIA/TIA-449 Transmission Speed Versus Distance
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 8 are also valid for V.35, X.21, and
EIA-530. EIA/TIA-449 and EIA-530 support 2.048-Mbps rates, and V.35 supports 2.048-Mbps
rates without any problems; we do not recommend exceeding published specifications for
transmission speed versus distance. Do so at your own risk.
4T Serial Connection Equipment
The 4T port adapter supports synchronous serial connections at speeds of up to 2 Mbps per
interface; the speed depends on the type of electrical interface used. Use EIA/TIA-232 for speeds of
64 kilobits per second (kbps) and below, and use X.21, EIA/TIA-449, V.35, or EIA-530 for higher
speeds.
EIA/TIA-232 Connections
The router (VIP) end of all EIA/TIA-232 adapter cables is a high-density 60-pin plug. The opposite
(network) end of the adapter cable is a standard 25-pin D-shell connector (known as a DB-25) that
is commonly used for EIA/TIA-232 connections. Figure 23 shows the connectors at the network end
of the adapter cable. The system console and auxiliary ports on the RP in the Cisco 7000 series (or
the RSP in the Cisco 7500 series) also use EIA/TIA-232 connections; however, the 4T port adapter
interfaces support synchronous serial connections, and the console and auxiliary ports only support
asynchronous connections. Use caution when connecting EIA/TIA-232 cables to the 4T receptacles.
EIA/TIA-232
Distances
EIA/TIA-449, X.21, V.35, EIA-530
Distances
Rate (bps) Feet Meters Feet Meters
2400 200 60 4,100 1,250
4800 100 30 2,050 625
9600 50 15 1,025 312
19200 25 7.6 513 156
38400 12 3.7 256 78
56000 8.6 2.6 102 31
1544000 (T1) – – 50 15