ZyXEL Communications COMET 336, User Manual

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22 Advanced Data Communications
4
Advanced Data Communications
This chapter is included as a general reference to the connectors, interfaces, protocols,
and standards used by the Comet 336, including definitions of many of the
communications-related terms used in this manual.
Front Panel LEDs
The Comet 336 has 9 front panel LEDs. Refer to the following tables for details on the
LED status indicators and their meanings.
LED State Indicates Status
MR Modem Ready
or Self-Test in
progress. Modem is ready for data communications.
HS High Speed Modem is operating at 2400bps or higher
CD Carrier Detect Modem has detected a valid carrier signal, or &C0 is set.
OH Off Hook Modem is accessing telephone line.
SD Send Data Flashes on/off rapidly when data is being transmitted from
modem to your computer.
RD Receive Data Flashes on/off rapidly when data is being transmitted from
computer to your. modem
TR Terminal
Ready Computer is ready for data communications.
AA Auto Answer Modem will automatically answer incoming calls.
PWR Power The modem is on and has power to operate.
DTE Interface
DTE and DCE are terms used in data communication. DTE stands for Data Terminal
Equipment and DCE stands for Data Communication Equipment. The computer or
terminal is the DTE and the modem is the DCE. The DTE interface used by the Comet
336 is an RS-232 with throughput speeds up to 115.2 Kbps.
Synchronous and Asynchronous Communications
There are two kinds of serial data communication. One is called synchronous, and the
other is called asynchronous. In synchronous communication, data is transmitted and
received bit by bit and is timed by an accompanying clock signal. In asynchronous
communication, data is sent character by character (or octet by octet), and the idle time
between characters is variable. Since no clock signal is sent, character timing is
recovered from the data itself.
A PC's COM1 and COM2 are asynchronous serial ports. Most PCs' and UNIX systems'
serial data communications are asynchronous. The serial data communication on an IBM
mainframe or mini is synchronous.