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+# SGSN_Tests.ttcn
+
+* external interfaces
+    * Gb (emulates PCU side NS/BSSGP + MS)
+    * GSUP (emulates HLR)
+    * VTY
+
+{% dot sgsn_tests.svg
+digraph G {
+  rankdir=LR;
+  SGSN [label="SGSN\nosmo-sgsn",shape="box"];
+  ATS [label="ATS\nSGSN_Tests.ttcn"];
+
+  ATS -> SGSN [label="Gb"];
+  SGSN-> ATS [label="Gp (GTP)"];
+  ATS -> SGSN [label="VTY"];
+}
+%}