add DOT graph showing NITB data structures and their references
diff --git a/openbsc/doc/osmo-nitb-data_structures.dot b/openbsc/doc/osmo-nitb-data_structures.dot
new file mode 100644
index 0000000..81955e8
--- /dev/null
+++ b/openbsc/doc/osmo-nitb-data_structures.dot
@@ -0,0 +1,33 @@
+digraph G {
+ net [label="gsm_network"]
+ bts [label="gsm_bts"]
+ trx [label="gsm_bts_trx"]
+ ts [label="gsm_bts_trx_ts"]
+ lchan [label="gsm_lchan"]
+ sub [label="gsm_subscriber"]
+ subcon [label="gsm_subscriber_conn"]
+ sccpcon [label="osmo_bsc_sccp_con"]
+ subgrp [label="gsm_subscriber_group"]
+
+ net -> bts
+ bts -> trx
+ trx -> ts
+ ts -> lchan
+
+ lchan -> ts
+ ts -> trx
+ trx -> bts
+ bts -> net
+
+ lchan -> subcon
+
+ subcon -> sub
+ subcon -> sccpcon
+ subcon -> lchan
+ subcon -> lchan [label="ho_lchan"]
+ subcon -> bts
+ subcon -> lchan [label="secondary_lchan"]
+
+ sub -> subgrp
+ subgrp -> net
+}