Cisco WS-C2950T-24 Hardware Installation Guide - Page 76

Network Cabling Specifications Chapter 2 Preparing for Router Installation Serial DTE or DCE Devices A device that communicates over a synchronous serial interface is either a DTE or DCE device. A DCE device provides a clock signal that paces the communications between the device and the router. A DTE device does not provide a clock signal. DTE devices usually connect to DCE devices. The documentation that accompanied the device should indicate whether it is a DTE or DCE device. (Some devices have a jumper to select either DTE or DCE mode.) Table 2-2 lists typical DTE and DCE devices. Table 2-2 Typical DTE and DCE Devices Device Type DTE Gender Male1 Typical Devices Terminal DCE Female2 PC Modem CSU/DSU Multiplexer 1. If pins protrude from the base of the connector, the connector is male. 2. If the connector has holes to accept pins, the connector is female. Signaling Standards Supported The synchronous serial ports available for the router support the following signaling standards: they are EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA-530. You can order a Cisco DB-60 shielded serial transition cable that has the appropriate connector for the standard you specify. The documentation for the device you want to connect should indicate the standard used for that device. The router end of the shielded serial transition cable has a DB-60 connector, which connects to the DB-60 port on a serial WAN interface card. The other end of the serial transition cable is available with a connector appropriate for the standard you specify. The synchronous serial port can be configured as DTE or DCE, depending on the attached cable (except EIA-530, which is DTE only). 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 Cisco Modular Access Router Cable Specifications document. 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 significantly degrades or is completely lost. Note Only the serial WAN interface card supports bit rates above 128 Kbps. Table 2-3 lists 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 Mb/s, but 4 Mb/s is commonly used. 2-10 Cisco 2900 Series and 3900 Series Hardware Installation Guide OL-18712-02