Application Notes; Serial Protocol Standards; What Is A Terminal Server? - GE Multinet 4 Instruction Manual

Digital Energy
Multilin
7.1

What is a Terminal Server?

7.1.1

Serial Protocol Standards

MULTINET4 MULTI-PORT SERIAL SERVER & MANAGED SWITCH – INSTRUCTION MANUAL
Multinet4 Multi-Port Serial Server
& Managed Switch
Chapter 7: Terminal Server
Terminal Server Application Notes
A Terminal Server is a device or software application that can pass data between a
standard serial protocol link and an IP-based network. The Terminal Server functionality of
the Multinet4 Series provides a service that encapsulates asynchronous serial data in a
TCP/IP stream. Service provisioning is flexible and allows a number of different
configurations as described below.
There are many techniques for passing serial binary data between two or more digital
systems. A number of popular methods based on standards published by the ITU-T are
commonly referred to as "serial" protocols. Two of the most popular of these interfaces are
EIA-232 (also know as RS-232) and EIA-485 (also known as RS-485).
Interfaces that support RS-232 (or some subset of the standard) are ubiquitous and found
on nearly all personal computers. They also appear on many embedded computing
devices where they are used to carry streaming data or provide access to a user console.
An RS-232 link provides full-duplex data and asymmetric control. One device on the link is
defined as the DTE (Data Terminal Equipment) and the other device is defined as the DCE
(Data Communications Equipment). Traditionally, a DTE was a computer system and a DCE
was a communications device such as a modem. Handshaking signals provide for flow
control as well as valid link detection. Data rates typically range from 150bps to 115Kbps
over distances up to 10 meters.
Interfaces that support RS-485 are less common; however, this protocol has a number of
advantages over RS-232. RS-485 can be configured as a 4-wire, full duplex channel or a 2-
wire, half duplex channel. It may also be operated in point-to-point or multi-point
topologies (RS-232 only supports point-to-point). Because the standard uses differential

Application Notes

7–1