[rcpilot-devs] RFC for AX.25 Private Unnumbered Information Frame Type

[Michael J. P. <mi...@vi...>]

I started a rough layout for the RFC.

Feel free to comment and add info.

Mike


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                                                                                                                           Michael J. Pawlowsky
Request for Comments:	                                                                                       Montreal, Quebec, Canada
Category: Informational	                                                                                       February 25, 2004



                                                  Private Unnumbered Information AX.25 Frame




Status of this Memo

This memo describes a new frame type for the AX.25 (Amateur Packet-Radio Link-Layer Protocol). This technique is experimental for the amateur UAV community.
Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.


AX.25

(Description of AX.25)




Abstract

For telemetry information to be useful in amateur UAVs the data refresh rate needs to be as high as possible. Current limitations imposed by over air data transfer rates make obtaining a refresh rate sufficient to be used for real time navigation difficult. By reducing some of the unnecessary portions of the AX.25 UI frame, we can increase the refresh rate significantly. The current UI Frame with no data in it requires 160 bits.
By removing the Address and PID fields, a savings of 120 bits can be achieved.

As an example using an information field of 48 bits the new total size for the frame would be 88 bits as opposed to 208 bits.  Using the UI frame at 1200 baud the maximum refresh rate obtainable would be approximately 5.8Hz. Using the new PUI frame type a refresh rate of approximately 13.6Hz is possible.

We may eliminate the address field since these frames are intended to be received by a single party. The PID may be eliminated as well since no layer 3 protocol is used.

(Suggest a new control for this frame type)




The Private Unnumbered Information Frame Format

The current format of the AX.25 UI frame is as follows:

Flag         | Address     | Control | PID     | Info.       | FCS    |Flag
01111110 |112/560 Bits| 8 Bits   | 8 Bits | N*8 Bits | 16 Bits | 01111110

The proposed format for the PUI is as follows:

Flag 	   |  Control |   Info.       | FCS     | Flag
01111110 |   8 Bits  |   N*8 Bits |	16 Bits | 01111110




Reference

[1] AX.25 Amateur Packet-Radio Link-Layer Protocol Version 2.0
October 1984.  Available from TAPR http://www.tapr.org/tapr/html/Fax25.html




Contributors

Val Petrov
Marlise Meyer



Author's Address

Michael J. Pawlowsky