Table of Contents

How to Select a Serial Cable

DTE or DCE
Signaling Standards
Connector Gender
Serial Connection Example

Serial Cable Part Numbers

Selecting a Serial Cable

This appendix provides the following information:

• How to select a serial cable to connect your serial device

• Cisco part numbers for serial cables that you can order

How to Select a Serial Cable

To select a serial cable, you must answer the following questions about the serial device that you plan to connect to the router serial port:

DTE or DCE

There are two types of devices that can communicate over a serial interface: DCE and DTE. A DCE provides a physical connection to a network and forwards traffic. A DTE connects to a network through a DCE device. Typically, a DTE device is connected to a DCE device (or vice versa) rather than another DTE device.

Check the documentation that ships with your serial device to determine if it is a DTE or DCE device. If you cannot find the information in the serial device documentation, refer to Table A-1. This table summarizes serial devices that can be connected to the router serial port and whether the device is considered a DTE or DCE device. The Cisco 805 router is a DTE device by default. Table A-2 describes the type of cable needed to connect a DTE or DCE device to your router.

Table A-1: DTE and DCE Devices

Serial Device	DTE	DCE	Selectable DTE or DCE1
Modems (asynchronous and synchronous)		X
Channel service unit/data service unit (CSU/DSU)		X
Multiplexers		X
Terminals	X
Routers			X
Hubs			X
Switches			X
Access server			X

1These serial devices usually have a jumper, switch, or software command that selects the DTE or DCE mode.

Table A-2: Cable Type Needed to Connect Serial Devices

Serial Device Type	Cable Type Needed
DTE	DCE
DCE	DTE

Signaling Standards

Several standards define the signaling over the serial connectors on the router and serial device, the serial cable, and the cable connectors. You can connect a serial device with the following types of connectors to the router serial port:

• EIA/TIA-232

• EIA/TIA-449

• EIA/TIA-530

• EIA/TIA-530A

• X.21

• V.35

Check the documentation that ships with your serial device to determine the type of serial connector on your serial device.

Connector Gender

If pins protrude from the base of a connector, the connector is male. If the connector has holes to accept the pins, the connector is female.

A DTE device typically has a male connector, while a DCE device typically has a female connector.

Examine the serial connector on your serial device to determine its gender.

Serial Connection Example

Figure A-1 shows a typical serial connection for the Cisco 805 router. In this example, the router, which is a DTE device, is connected to a CSU/DSU or modem, which are DCE devices.

Because the serial devices are DCE, you should use a DTE cable to connect the router and the CSU/DSU or modem. (For more information on the cable type needed to connect a serial device, refer to Table A-2.)

Given these characteristics, the appropriate serial cable to connect the router and the CSU/DSU or modem is a DTE V.35 male cable.

Serial Cable Part Numbers

Table A-3 summarizes serial cables that you can order from Cisco.

Posted: Wed Jun 16 11:29:54 PDT 1999
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