Ref: 10630001
Title: GS/X.25-IP Version 2.0 Functionality
date: 11/07/89

Copyright 3Com Corporation, 1991.  All rights reserved.

This topic explains the functions of the newly released GS/X.25-IP.

The GS/X.25-IP Version 2.0 supersedes the product GS/1-IP SW/20-IP-X.25
release 10000.  The previous product was strictly a X.25 IP router.
The new product, in addition to X.25 IP routing, will have Connection Service
support for PAD-connected terminals.

The Connection Service provides a X.3 PAD-Telnet gateway function.  This
new function will ONLY allow incoming calls from PAD-connected terminals
over X.25 networks to TCP/IP hosts.  The capability to issue OUTGOING
calls to X.25 hosts from a TCP/IP host wherein the GS/X.25-IP gateway
acts as a PAD is not yet available.  The maximum number of PAD-connected
terminals is 48.


Scenarios for Establishing a Connection

The user can establish connections to TCP/IP hosts via two methods,
Automatic Connection Service and Extended Connection Service.  The
Automatic Connection Service allows a user to make an end-to-end
connection to the target host in one step.  The Extended Connection
Service allows the user to connect to the GS/X.25-IP gateway first, and
then make use of the Communication Server Connection Services to get
more flexibility.

Both the Automatic Connection Service and the Extended Connection
Service can be disabled.  The default is for both services to be on.


Automatic Connection Service

When specifying the gateway X.25 address, the PAD user includes the eventual
destination of the call in the Call User Data portion of the X.28 selection
command.  The destination can be a NAME for use by a Name Server or an actual
destination IP address.  Since the Call User Data field is limited to 12
characters, NAMEs can be up to twelve characters.  Also, IP addresses must
fill the 12-character Call User Data.  Thus, all leading and trailing
zeros should be included, but decimal points should be excluded.  For
example, the IP address 192.10.205.5 would be specified in the Call User
Data field as "192010205005".


Automatic Connection Service Using the Subaddress Field

When specifying the GS/X.25-IP X.25 address, the PAD user appends two
subaddress digits.  The X.25 network over which the connection is to be
made must support subaddressing.  When receiving an incoming call, the
GS/X.25-IP will check the called two digits; the gateway does not support
one-digit subaddress and it reserves the subaddress 00 for backward
compatibility.  The GS/X.25-IP will then use the subaddress as an index into
a table defined by the network manager on the GS/X.25-IP to get the
appropriate Call User Data information.   This will allow up to 99 host
names, port numbers, rotary numbers or IP addresses to be reached
automatically without the user having to bother about the Call User Data
field itself.  This mechanism will occur only if the Call User Data field is
limited to the PAD Identifier.  The 99 entries are on a per line basis and
are defined in the table as they would be defined in the Call User Data
field.

When a successful connection has been established, a PAD profile is issued
to the PAD by the GS/X.25-IP Connection Service.  The PAD profile can
be set up on a per line or a per port basis.


Extended Connection Service

When specifying the gateway X.25 address, the PAD user includes a port
number, a rotary number, or no number in the Call User Data field of the
X.28 selection command.  When the user is connected to the
GS/X.25-IP Connection Service User Interface, the Connection Service
will issue a PAD profile to set up a transparent connection between the
PAD and the GS/X.25-IP gateway.  Connections can then be established to
TCP/IP hosts as described in the "TCP/IP Connection Service Users
Guide".

