APRS101.pdf is Obsolete

APRS101.pdf was the APRS protocol reference written in 2000.  It is missing decades of corrections, clarifications, and new features. 

Implementing a product from this is likely to produce something incompatible with contemporary practices.

 

 

For Developers:

 

For a successful implementation, you need to track down and digest:

·        The original specification.

·        20+ years of corrections, clarifications, and new features.

·        Essential aspects of AX.25.

·        Tribal knowledge about AX.25 and APRS.

The tedious work of merging it all together has been done here:  https://github.com/wb2osz/aprsspec .

·        APRS12b.pdf is version 1.2 draft B.

·        APRS12c.pdf is version 1.2 draft C.

·        etc.

·        APRS-Digipeater-Algorithm.pdf

Your feedback is welcome.

 

For Everyone:

 

Trying to understand APRS packets can be confusing.  Some are fairly obvious but others are really obscure.  This introduction will help you decipher these mysterious signals and spot errors.   This deals only with the human readable TNC-2 monitoring format.  It does not cover AX.25 in HDLC frame format.

Understanding-APRS-Packets.pdf    in   https://github.com/wb2osz/aprsspec .

My goal is to produce a more approachable introduction rather than telling people to read the protocol specification. 

About 1/3 of this document is devoted to errors observed locally.  Some are caused by flawed implementations; others are caused by user error.   Read this document carefully if you don’t want to end up as an example of what not to do.