Minimal version of the LTE downgrade analyzer

This also renames the lte_parser crate to telcom_parser, since it'll
handle any 2G or 3G parsing going forward.

telcom-parser/README.md

@@ -0,0 +1,26 @@
+# Autogenerated telcom packet parsing
+
+This crate contains [ASN.1](https://en.wikipedia.org/wiki/ASN.1) specs for various telcom message payloads, as well as autogenerated
+Rust code for parsing these messages. We're using [hampi](https://github.com/ystero-dev/hampi/) as a parser generator, and it seems
+3GPP protocols are encoded in the unaligned Packed Encoding Rules (or uPER) codec.
+
+## Generating the parser
+
+To install the hampi compiler, run:
+
+```
+> cargo install asn1-compiler
+```
+
+To generate the parser for LTE RRC, run:
+
+```
+> hampi-rs-asn1c --codec uper --derive clone --derive partial-eq --derive serialize --module src/lte_rrc.rs -- specs/EUTRA* specs/PC5-RRC-Definitions.asn
+```
+
+## Sourcing the ASN.1 files
+
+3GPP, who develops the standards for 4G (and all the other G's) publishes ASN.1 specs for their protocols in these horrific Microsoft Word docs (e.g. [here](https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2440)). The ASN.1 blocks are denoted by `--ASN1START` and `--ASN1STOP` text, so extracting them automatically is possible using a script like [hampi's](https://github.com/ystero-dev/hampi/blob/master/examples/specs/parse_spec.py). Instead of doing this ourselves, we just sourced ours from [these](https://obj-sys.com/products/asn1apis/lte_3gpp_apis.php#lte_4g_apis).
+
+# TODO
+* implement proof of concept binary using this to parse QMDL, summarize the packets