TCP/IP via X.25
10 Feb 86 08:23:00 PST


The X.25 connection you mentioned in your 8 February message describes,
what is known as "Basic Mode" DDN X.25. Although TCP/IP is used for
such things as data integrity, 'Basic Mode' service provides communication
only between a X.25 DTE and other X.25 DTE's. Specifically, only
a X.25 Host can communicate with another X.25 Host on the DDN.

As DCA has mandated that all host be interoperable with each other another
form of X.25 has been devised which is called "Standard Mode". This is
to allow hosts which have been previously connected to the net, either
with 1822 or 1822-J (HDH) connections, to communicate with X.25 hosts.
TCP/IP is used as the upper-level protocols to provide continuity and
full interoperablity.

As you may or may not know, DCA is in the process of qualifying various
vendors implementations of the DDN X.25 specification. It is important
for user evaluation to determine if the vendor has a fully qualified
product in accordance with the test scenarios of the DDN X.25 Standard
Service for achieving full interoperability.

For additional information contact the NIC and request the circular
entitled: "Defense Data Network X.25 Host Interface Specification,
December 1983.


Gary Krall

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