DEC VAX 4000 300 Manual page 34

NOTE: Printers equipped with a microprocessor (intelligent printers) may
require modem control signals to function correctly. Do not attach a printer
requiring modem control signals to a controller with no modem support.
Check your printer documentation to determine the proper communications
interface for your printer.
Communications controllers with modem support allow you to communicate
over telephone lines. With a modem connected to your system, you can
access other computers and you can dial into your system from a remote
terminal or computer.
Computers transmit digital signals, while telephone lines (with the
exception of digital leased lines) transmit analog signals. When two
computers communicate over telephone lines, a modem is required at both
the transmitting and receiving ends of the line. At the transmitting end, the
modem converts digital signals from the computer (or terminal) to analog
signals prior to transmission. At the receiving end, another modem converts
the analog signals back into digital signals the computer can process.
The degree of modem support depends on the number of modem control
signals recognized by the device. Full modem support (according to Digital
standards) requires recognition of eleven signals. The CXY08 module
supports up to eight serial lines with full modem support.
Synchronous Serial Controllers
Synchronous serial controllers provide high-speed connections between
systems. Communication between synchronous devices depends on time
intervals that are synchronized before transmission of data begins.
Synchronous devices can also have modem support.
DECservers
DECservers are terminal servers (a combination of hardware and software)
that allow you to connect multiple terminals or printers to hosts in an
Ethernet Local Area Network (LAN).
Terminal servers perform the functions of traditional data terminal
switches but multiplex the lines over the Ethernet. Using a DECserver
offloads communications processing from the host system.
Network Controllers
Network communications controllers allow you to connect to an Ethernet
LAN or other network type. With a network connection and appropriate
DECnet software, you can use network services, such as mail; access data
stored on other systems; perform operations, such as editing and printing on
remote systems; and share resources, such as laser printers. The network
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