Cisco Systems CISCO1841-HSEC/K9-RF manual Distance Limitations

Chapter 5 Cable Information and Specifications for Cisco 1800 Series Routers (Modular)

Preparing to Connect to a Network

The synchronous serial port can be configured as DTE or DCE, depending on the attached cable (except EIA-530, which is DTE only). To order a shielded cable, contact customer service. See the “Obtaining Documentation and Submitting a Service Request” section on page 1-15.

Note All serial ports configured as DTE require external clocking from a channel service unit/data service unit (CSU/DSU) or other DCE device.

Although we do not recommend manufacturing your own serial cables (because of the small size of the pins on the DB-60 serial connector), cable pinouts are provided in Cisco Modular Access Router Cable Specifications.

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 is significantly degraded or completely lost.

Table 5-2lists 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 Mbps, but 4 Mbps is commonly used.

Table 5-2	Serial Signal Transmission Speeds and Distances
				Distance for
		Distance for		EIA/TIA-449, X.21, V.35,
		EIA/TIA-232		and EIA-530
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
38400		12	3.7	256	78
56000		8.6	2.6	102	31
1544000 (T1)		—	—	50	15

Balanced drivers allow EIA/TIA-449 signals to travel greater distances than EIA/TIA-232 signals. Typically, EIA/TIA-449 and EIA-530 can support a 2-Mbps rate, and V.35 can support a 4-Mbps rate.

Asynchronous/Synchronous Serial Module Baud Rates

The following baud-rate limitations apply to the slow-speed serial interfaces in the asynchronous/synchronous serial modules:

•Asynchronous interface—Maximum baud rate is 115.2 kbps.

•Synchronous interface—Maximum baud rate is 128 kbps, full-duplex.

Cisco 1800 Series Routers (Modular) Hardware Installation Guide

5-4 OL-5876-03