3Com 5000 Series Installation Manual page 41

3Com Router 5000 Family
Installation Guide
Caution:
The baud rate should not exceed 64kbps when the V.24 cable operates in synchronous
mode.
DTE and DCE
Synchronous serial interface can operate in both DTE and DCE mode. For two devices
connected directly, one should operate in DTE mode, and the other should operate in
DCE mode. The device at the DCE side provides a synchronous clock and specifies the
transmission rate, while the device at the DTE side accepts the synchronous clock and
communicates at the specified baud rate. Usually, the router serves as a DTE device.
To determine whether the device connected to the router is a DTE or DCE, please refer
to the manual that came with the device. Also the following table will be helpful in
identifying DTE and DCE. Usually, the PC or Router serves as a DTE device and the
Modem, Multiplexer or CSU/DSU serves as a DCE device.
In general, the asynchronous serial interface is connected to an external Modem or a
Terminal Adapter (TA) to work as the dial-up interface. In this case, it is unnecessary to
determine whether the device is DTE or DCE, and just choose an appropriate baud
rate.
2) Synchronous/asynchronous serial interface cable
The WAN interface of the router is a DB50 receptacle. Proper connection cable needs
to be selected for the protocol applied. By far, nine types of synchronous/asynchronous
serial interface cables are available. One end of all the nine types of cables is DB50
connector, the other end (network end) varies with the cable type, which can be:
V.24 (RS232) DTE cable: DB25 (male) connector
V.24 (RS232) DCE cable: DB25 (female) connector
V.35 DTE cable: 34PIN (male) connector
V.35 DCE cable: 34PIN (female) connector
X.21 DTE cable: DB15 (male) connector
X.21 DCE cable: DB15 (female) connector
RS449 DTE cable: DB37 (male) connector
RS449 DCE cable: DB37 (female) connector
RS530 DTE cable: DB25 (male) connector
The following figures show the cable assembly of all these types:
V.24 (RS232) DTE cable assembly
3Com Corporation
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Chapter 4 Installation of the Router