[doc] Define 'gsup' group with proper name, add intro text
Change-Id: Ieee6213dc5aad082a2d439c7418b51f281b80b1a
diff --git a/include/osmocom/gsm/gsup.h b/include/osmocom/gsm/gsup.h
index 36e5c84..8daf460 100644
--- a/include/osmocom/gsm/gsup.h
+++ b/include/osmocom/gsm/gsup.h
@@ -1,5 +1,20 @@
-/*! \file gsup.h
- * Osmocom Generic Subscriber Update Protocol message encoder/decoder. */
+/*! \defgroup gsup Generic Subscriber Update Protocol
+ * @{
+ *
+ * The Generic Subscriber Update Protocol (GSUP) is an Osmocom-specific
+ * non-standard protocol replacing MAP as the protocol between
+ * MSC/VLR/SGSN and HLR in a 3GPP cellular communications network.
+ *
+ * It was designed around the same transactions and architecture as the
+ * MAP messages/operations, but without the complexity of TCAP and MAP,
+ * and without the need for ASN.1 encoding.
+ *
+ * The purpose is to keep protocol complexity out of OsmoSGSN and
+ * OsmoMSC, while providing a clean path to an external GSUP to MAP
+ * translator.
+ *
+ * \file gsup.h
+ * Osmocom Generic Subscriber Update Protocol message encoder/decoder. */
/*
* (C) 2014 by sysmocom s.f.m.c. GmbH, Author: Jacob Erlbeck
* (C) 2016 by Harald Welte <laforge@gnumonks.org>
@@ -163,3 +178,5 @@
int osmo_gsup_decode(const uint8_t *data, size_t data_len,
struct osmo_gsup_message *gsup_msg);
void osmo_gsup_encode(struct msgb *msg, const struct osmo_gsup_message *gsup_msg);
+
+/*! @} */