HP X.25/9000 Programmer's Guide

Chapter 1 3
Introduction to X.25 Programmatic Access
X.25 Product Description
X.25 Product Description
The X.25 link software and hardware enable an HP system to
communicate with other HP and non-HP hosts by way of an X.25 Packet
Switching Network (PSN).
The CCITT X.25 Recommendations describe the packet interface
between a DTE (Data Terminating Equipment) and a DCE (Data
Communications Equipment). The DTE is a device (computer or
terminal) which connects to an X.25 PSN. The DCE interface is supplied
by the PSN to enable the DTE to connect to the network. This type of
connection is usually made over telephone lines via a modem.
Figure 1-1, “Typical X.25 Network Connection,” illustrates a typical X.25
network configuration between an HP 9000 and a remote host using an
X.25 PSN.
Figure 1-1 Typical X.25 Network Connection
A direct connection can be made via a modem eliminator. A modem
eliminator provides the clocking mechanism necessary to synchronize
signals between a DTE and a DCE. Two X.25 interfaces can be connected
in this way, but one of them must be configured as a DCE. This type of
configuration is called a “back-to-back configuration.”
Figure 1-1, “Typical X.25 Network Connection,” illustrates a typical
back-to-back configuration with a remote host. The remote host can be
any type of processor, including another HP 9000, or any device capable
of fulfilling the requirements of a DTE (or DCE in the back-to-back
configuration).
DCE
HP 9000 Remote Host
DTE
X.25
DCE DTE
X.25 PSN
36960-90061.bk Page 3 Friday, November 10, 2000 3:42 PM