--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/doc/Codec-library-depend	Mon Nov 21 01:01:39 2022 -0800
@@ -0,0 +1,23 @@
+One important component of Themyscira Wireless system sw, specifically
+themwi-mgw, implements speech transcoding between GSM codecs on the inside and
+G.711 on the outside.  This essential function creates a dependency on some
+specialized libraries that implement the codecs which need to be supported.
+The following codec libraries are currently required:
+
+1) libgsm, the original GSM 06.10 implementation from 1990s;
+
+2) gsm-codec-lib developed by Mother Mychaela:
+
+https://www.freecalypso.org/hg/gsm-codec-lib/
+
+This gsm-codec-lib collection provides two libraries; as of this writing, one
+is already implemented while the other is in the plans:
+
+2a) libgsmfrp is the Rx DTX handler for the original FR codec, a front-end
+    preprocessor that sits in front of libgsm decoder.  This preprocessor
+    implements functions specified in GSM 06.11, 06.12 and 06.13, and these
+    functions are required (not optional) for a network-side implementation of
+    GSM FR codec in a TRAU-like component.
+
+2b) libgsmefr will be a librified (turned into a library) version of the
+    official reference implementation (from ETSI) of GSM EFR codec.