Appendix B - Kiss Tnc Specification - AEA PK-232 Technical Reference Manual

PK-232 TECHNICAL MANUAL APPENDIX B – KISS TNC Specification
APPENDIX B – KISS TNC SPECIFICATION
The KISS TNC: A simple Host-to-TNC communications protocol
Mike Chepponis, K3MC
Phil Karn, KA9Q
Presented at the ARRL 6th Computer Networking Conference, Redondo Beach CA, 1987.
Translated to HTML by KA9Q, January 1997.
ABSTRACT
The KISS ("Keep It Simple, Stupid") TNC provides direct computer to TNC communication using a
simple protocol described here. Many TNCs now implement it, including the TAPR TNC-1 and TNC-
2 (and their clones), the venerable VADCG TNC, the AEA PK-232/PK-87 and all TNCs in the Kant-
ronics line. KISS has quickly become the protocol of choice for TCP/IP operation and multi-connect
BBS software.
1. Introduction
Standard TNC software was written with human users in mind; unfortunately, commands and re-
sponses well suited for human use are ill-adapted for host computer use, and vice versa. This is
especially true for multi-user servers such as bulletin boards which must multiplex data from sev-
eral network connections across a single host/TNC link. In addition, experimentation with new link
level protocols is greatly hampered because there may very well be no way at all to generate or re-
ceive frames in the desired format without reprogramming the TNC.
The KISS TNC solves these problems by eliminating as much as possible from the TNC software,
giving the attached host complete control over and access to the contents of the HDLC frames
transmitted and received over the air. This is central to the KISS philosophy: the host software
should have control over all TNC functions at the lowest possible level.
The AX.25 protocol is removed entirely from the TNC, as are all command interpreters and the
like. The TNC simply converts between synchronous HDLC, spoken on the full- or half-duplex radio
channel, and a special asynchronous, full duplex frame format spoken on the host/TNC link. Every
frame received on the HDLC link is passed intact to the host once it has been translated to the
asynchronous format; likewise, asynchronous frames from the host are transmitted on the radio
channel once they have been converted to HDLC format.
Of course, this means that the bulk of AX.25 (or another protocol) must now be implemented on
the host system. This is acceptable, however, considering the greatly increased flexibility and re-
duced overall complexity that comes from allowing the protocol to reside on the same machine
with the applications to which it is closely coupled.
It should be stressed that the KISS TNC was intended only as a stopgap. Ideally, host computers
would have HDLC interfaces of their own, making separate TNCs unnecessary. Unfortunately,
HDLC interfaces are rare, although they are starting to appear for the IBM PC. The KISS TNC
therefore becomes the "next best thing" to a real HDLC interface, since the host computer only
needs an ordinary asynchronous interface.
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