Update README.md

README.md

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 # M17_spec
 
-Protocol specification for the [M17 Project](http://m17project.org/).
+[M17 Project](http://m17project.org/) is a modern, digital radio protocol built by hams, for hams. 
+This repository contains the specification describing it exhaustively, from top to bottom. It is still a work in progress, meaning that this repository is meant to be updated now and then. After a few years of development, almost all of the changes are just to supplement the specification with new functions or improve the document.
 
-M17 is a modern, digital radio protocol built by hams, for hams. 
-It is still a work in progress, and this is the living specification of the protocol.
+The specification can be conveniently browsed [here](https://spec.m17project.org/).
 
-The specification can be viewed [here](https://spec.m17project.org/).
+# Table of contents
+**Part I - Air Interface**
+* M17 RF Protocol: Summary
+* Glossary
+* Physical Layer
+    * 4FSK generation
+        * Preamble
+        * Bit types
+        * Error correction coding schemes and bit type conversion
+* Data Link Layer
+    * Stream Mode
+    * Packet Mode
+    * BERT Mode
+* Application Layer
+    * Amateur Radio Voice Application
+    * Packet Application
+
+**Part II - Internet Interface**
+* M17 Internet Protocol (IP) Networking
+    * Standard IP Framing
+    * Control Packets
+
+**Appendix**
+* Address Encoding
+    * Callsign Encoding: base40
+    * Callsign Formats
+* Randomizer sequence
+* Convolutional Encoder
+* Golay Encoder
+* Code Puncturing
+* Interleaving
+* BERT Details
+* KISS Protocol
+    * References
+    * Glossary
+    * M17 Protocols
+    * KISS Basics
+    * Packet Protocols
+    * Stream Protocol
+    * Mixing Modes
+    * Implementation Details
+* File Formats