3Com 3C13701 Installation Manual page 32

32 C 4: I
HAPTER NSTALLATION OF THE
R
OUTER
Table 17 Transmission rate and transmission distance of V.24 (RS232)/V.35 cable
V.24 (RS232)
Maximum
transmission
Baud rate (bps) distance (m)
2400 60
4800 60
9600 30
19200 30
38400 20
64000 20
115200 10
— —
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.
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
■
V.35
Maximum transmission
Baud rate (bps) distance (m)
2400 1250
4800 625
9600 312
19200 156
38400 78
56000 60
64000 50
2048000 30