diff --git a/doc/protocols_around_hnbgw.txt b/doc/protocols_around_hnbgw.txt
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+Who Talks What Around the Home Node B Gateway
+=============================================
+(wip 2016-01-11)
+
+
+        +------------+           +--------+          +----------+
+ UE <-->| hNodeB     |<--Iuh---->| HNB-GW |<--IuCS-->| OsmoCSCN |
+ UE <-->| femto cell |     ...-->|        |          +----------+
+        |            |           |        |
+        +------------+<--GTP-U   |        |
+                              \  |        |          +------+           +------+
+                              |  |        |<--IuPS-->| SGSN |<--GTP-C-->| GGSN |
+                              |  +--------+          +------+   GTP-U-->|      |
+                              |                                /        +------+
+                              \_______________________________/
+
+
+
+                      Iuh                         IuCS/IuPS
+
+NAS                   +----+----+                 +----+----+
+Non-Access Stratum    | CC | MM |                 | CC | MM |
+- - - - - - - - - - - +----+----+-------+         +----+----+
+                      | RANAP   |       |    H    | RANAP   |
+Access Stratum        +---------+ HNBAP |    N    +---------+ - - SCCP USER SAP
+                      | RUA     |       |    B    | SUA     |  \
+                      +---------+-------+    -    +---------+  |
+                      |        SCTP     |    G    | SCTP    |  } SIGTRAN
+                      +-----------------+    W    +---------+  |
+                      |        IP       |         | IP      |  /
+                      +-----------------+         +---------+
+
+
+Various SIGTRAN implementations:
+
+                IuCS/IuPS
+                  usual
+                   |     simplest
+                   |       |
+                   v       v
+  +------+------+------+-----+
+  | SCCP | SCCP |      |     |
+  +------+------+ SCCP |     |
+  | MTP3 | MTP3 |      |     |
+  +------+------+------+ SUA |
+  | MTP2 |      |      |     |
+  +------+ M2UA | M3UA |     |
+  | M2PA |      |      |     |
+  +------+------+------+-----+
+  |           SCTP           |
+  +--------------------------+
+  |            IP            |
+  +--------------------------+
+
+UE (User Endpoint) == MS (Mobile Subscriber) == mobile device
+CSCN (Circuit Switched Core Network) == OsmoNITB without BSC
+