Introduction to Networking for NonStop S-Series Servers

Introduction to Networking for HP NonStop S-Series Servers—520670-005
6-1
6 Device-Specific Connections
Data communications permits the exchange of information among systems and
devices that work together to perform a business function. The devices can range from
workstations to automated teller machines, to factory robots, to gasoline pumps, to
hand-held devices. Each device is likely to be manufactured by a different vendor, and
each can follow a unique set of protocols for physically and logically connecting to
other devices and systems.
An HP NonStop S-series server supports a wide range of device connectivity protocols,
protecting your investment in existing equipment and allowing you to use those devices
best suited to your particular application. This section describes the HP products that
enable you to connect a wide range of devices to an HP NonStop S-series server.
A Brief Look at Communications Protocols on this page discusses the communications
protocols that govern the transmission of data between a device and a host computer.
Following that subsection, types of connections are covered in the following order:
•
Industry-Standard Connections and HP Terminals on page 6-3
•
IBM Hosts on page 6-9
•
Workstations on page 6-11
•
Other Devices on page 6-13
A Brief Look at Communications Protocols
Before addressing device connectivity, you should be acquainted with the
communications protocols that govern the transmission of data between a device and
a host computer.
Data-link control protocols are sets of rules that define how data is transferred and
received between devices on a data link and how errors are handled. There are three
main groups of data-link control protocols—asynchronous, byte-synchronous, and
bit-synchronous—that correspond to two types of data transmission, which are
described in the following subsections:
•
Asynchronous Data Transmission on this page
•
Synchronous Data Transmission on page 6-2
Asynchronous Data Transmission
In asynchronous data transmission, data is transmitted and received one character
at a time, with each character preceded by a start bit and followed by one or more stop
bits. The start bit tells the receiver that a character has arrived, and the stop bits tell the
receiver where the character ends. Some asynchronous devices have a block mode
in which the device saves characters, transmitting them only when the Enter or Return
key is pressed.
Asynchronous protocols are most commonly used to connect a host system with
devices that have limited buffer space (memory). Most of these protocols support