Ref: 99980084
Title: New Products - GS/1-X.25 Overview
Date: 6/1/87

Copyright 3Com Corporation, 1991.  All rights reserved.

Overview

Bridge Communications has combined the GS/1 and the CS/1-X.25
into one new product, the GS/1-X.25.  The GS/1-X.25 is a
versatile product that combines the functions of:

*   X.25-to-Ethernet gateway

*   XNS router across an X.25 network

*   Virtual PAD

*   X.25 switch

*   Front-end processor

Its high-performance 68000-based architecture supports up to
eight synchronous ports with an aggregate line rate of 304K bps.
The GS/1-X.25 offers three different loading options: RS-232, RS-
422, and V.35.

The GS/1-X.25 is compatible with all Bridge XNS-based products
and fully participates in the Bridge network management
functions.

.h1;Features and Benefits

.h2;Versatile Configuration

The predominant feature of the GS/1-X.25 is its great
flexibility, making it useful for many different applications.
In addition, most of the options are configurable on a per-line
basis.  Each X.25 link can be individually configured as a DTE
(Data Terminal Equipment) or as a DCE (Data Circuit Terminating
Equipment).  In DTE mode, the GS/1-X.25 allows devices located on
a Bridge Ethernet/XNS network to communicate either with X.25
devices connected to the PDN or with other devices attached to a
remote Bridge LAN.

*   In DCE mode, the GS/1-X.25 serves as a front-end processor to
connect minicomputers, mainframes, and workstations
supporting an X.25 interface to a Bridge XNS-based network.

*   The interconnection service allows two remote Bridge LANs to
be interconnected through an X.25 network.  In this
configuration, the GS/1-X.25 acts as an XNS router.  XNS
packets including IDP and SPP headers are carried as data
across the X.25 network.

*   The connection service provides end-to-end connection at the
presentation level (layer 6 of the ISO model), as well as
X.29 compatibility.  This is achieved by translating X.3
parameters into VT parameters.  The connection service
feature opens up a wide variety of applications.  For
example:

-   A terminal connected to a PAD attached to a PDN can
connect to any device located on the Bridge Ethernet/XNS
network.  This can be performed either via a direct
passthrough service using the ClearingHouse name
mechanism or in two steps connecting first to the Bridge
user interface and then to the final destination.  The
access to the user interface can also be used to perform
network management functions.

-   A terminal on a Bridge Communications Server can connect
to an X.25 host on the PDN.

-   A Terminal on a Communications Server can connect to an
X.25 host attached to the Ethernet via a GS/1-X.25.

-   The GS/1-X.25 configured as a DCE can be used as a front-
end processor to any X.25 host.

-   A host on the PDN can execute a file transfer from a host
located on the Ethernet.

.h2;Standard Protocols

The interface to the X.25 host and the public data network is
through certified X.25 Level 1 to 3 protocols.  In addition, X.3/
X.28/X.29 protocols are used to support the selection of terminal-
to-host parameters.  The GS/1-X.25 provides dynamic internetwork
routing using the RIP (Routing Internetwork Protocol).

.h2;High Performance

The GS/1-X.25 supports 48 sessions.  They can either be
dispatched among different physical lines or concentrated on one.
When the GS/1-X.25 is configured for interconnection service,
more than 48 Communications Server sessions can go through the GS/
1-X.25.  In this case, a GS/1-X.25 session can be considered as a
pipe in which XNS packets for possibly more than one session
travel from one network to the other.  The number of sessions
created increases as the traffic becomes heavier.

.h2;Network Management and Security

The GS/1-X.25 offers full participation in Bridge Network
Management, audit trail, and name service:

*   Network management commands show Ethernet network
statistics and connection information, as well as X.25
line status.

*   The GS/1-X.25 participates in the Network Control Server
audit trail.

*   Although floppy-based, the GS/1-X.25 can be rebooted from
a Network Control Server using the reboot command.

*   The lines can be configured to bar incoming and outgoing
calls.  This feature allows unauthorized calls to be
screend for security purposes.

*   A passthrough service using ClearingHouse names is
offered for incoming calls.  This greatly simplifies
connections made from the X.25 network.  The GS/1-X.25
also supports nested ClearingHouse names.

*   Total transparency for prcoessing incoming calls.  When
this net feature is selected on a line, two X.25 devices
connected together through the GS/1-X.25 communicate on
an end-to-end basis.  X.25 transactions such as X.3
parameters reading or setting, transmission of interrupt
or reset packets, or transmission of packets with the Q-
bit or the M-bit set are passed transparently by the GS/1-
X.25.

*   The GS/1-X.25 supports global rotaries when the
connection is established from the user interface and
when the incoming call uses the passthrough mechanism.

.h1;Applications

In order to best use the GS/1-X.25, it is important to understand
its versatility and its many possible applications.  Below is a
list of typical configurations.

.h2;Interconnection Service

Two GS/1s act as XNS routers.  XNS packets are encapsulated in
X.25 packets and carried from one LAN to the other across the
X.25 network.

.h2;Front-End Processor (Connection Service)

The GS/1-X.25 can act as a front-end processor to any host with
an X.25 interface.  If appropriate software packages reside in
the respective operating systems, host-to-host file transfer can
be performed.  A terminal on the LAN can also connect to the X.25
hosts.  The Communications Server is then considered as a PAD by
the host, which can read and set X.3 parameters.

.h2;PAD on a PDN to a LAN (Connection Service)

A terminal attached to a PAD on the PDN can connect to any device
on the LAN.  The connection can be performed using the total
transparency feature.  In this case, X.25 transactions will be
done on an end-to-end basis.  If total transparency is not
selected, the user can connect either to the GS/1-X.25 user
interface and then to the final destination or to the host
directly using the passthrough and ClearingHouse name mechanism.

.h2;Term on the LAN to X.25 Host on the PDN (Connection
Service)

This configuration can be useful to connect to a large database
located on an X.25 host on a PDN.

.h1;Certifications

The GS/1-X.25 has been certified with the following public and
private data networks:

*   Telenet (U.S.)

*   Tymnet (U.S.)

*   Uninet (U.S.)

*   PSS (U.K.)




