Ref: 10630009
Title: GS1-XNS Virtual Circuit Assignment and Limitations
Date: 11/29/90

Copyright 3Com Corporation, 1991.  All rights reserved.

This topic explains how the 128 virtual circuits available on
the GS1-XNS (MCPU12) gateway can be allocated.

The gateway has two functions in which virtual circuits are allocated:
Connection Service and Routing.  Connection Service maps one virtual circuit
for each incoming or outgoing X.25 Incoming Call or X.25 Call Request.  The
number of users that issue Connection Service calls is limited to the number
of ports that are available.  On the MCPU12 GS1-XNS, 48 ports are available.
Thus, if all 48 ports are to be defined for Connection Service, then 48
virtual circuits must be available to allow all ports to be active at the
same time.

When defining the routing function, there is a limit of four virtual circuits
per remote network.  If 20 remote networks are defined with four
virtual circuits per remote network, 80 virtual circuits are required.  If
you add the 80 virtual circuits to the 48 used for Connection Service on an
MCPU12 GS1-XNS, this would result in a total of 128 virtual circuits.

If only routing is to be supported, then the limitation of 128 virtual
circuits is based upon the combination of the defined virtual circuits per
remote network, multiplied by the number of remote networks defined.  The
range of virtual circuits assigned to a remote network is from 1 to 4.

The specification of virtual circuits per remote networks is defined during
Sysgen.  To enable the specification, use Option 3, IDP/XDG Parameters,
followed by Option 5, Logical Channels Per Remote Net.

The number of virtual circuits assigned for connection service use is based
on the number virtual ports assigned to a line and the number of virtual
circuits assigned to that line.  Virtual port assignment is available via
Sysgen Option 6, Virtual Terminal Parameters, followed by Option 6, Virtual
Port to Physical Line Mapping.  The number of virtual circuits assigned to a
line must take into account the total number of virtual circuits to be
dedicated to routing plus the number of virtual ports assigned to that line.
The number of virtual circuits dedicated to a line are Sysgened via Option 9,
X.25 Parameters, followed by Option 3, X.25 Level 3 Parameters.  The next
menu requires selection of Option 10, Number of Logical Channels (virtual
circuits).
