msc {
  hscale="2";
  hnb[label="HNB"],rua[label="OsmoHNBGW\nRUA FSM / HNBAP"],sccp[label="OsmoHNBGW\nSCCP FSM"],cn[label="CN"];

  hnb <=> rua [label="RANAP/RUA\n(Iuh)"];
  rua <=> sccp [label="FSM events"];
  sccp <=> cn [label="RANAP/SCCP/M3UA\n(IuCS, IuPS)"];

  ...;
  ...;
  --- [label="Create a new context map (always from HNB)"];
  hnb => rua [label="RUA Connect\nRANAP InitialUE-Message\nDTAP Location Updating Request"];
  rua rbox sccp [label="hnbgw_context_map_alloc()"];
  rua abox rua [label="MAP_RUA_ST_INIT"];
  sccp abox sccp [label="MAP_SCCP_ST_INIT"];
  rua rbox rua [label="MAP_RUA_EV_RX_CONNECT\ndata = ranap_msg"];
  rua abox rua [label="MAP_RUA_ST_CONNECTED"];
  rua => sccp [label="MAP_SCCP_EV_TX_RANAP_MSG\ndata = ranap_msg"];
  sccp abox sccp [label="MAP_SCCP_ST_WAIT_CC"];
  sccp => cn [label="SCCP Connection Request\nRANAP InitialUE-Message\nDTAP Location Updating Request"];
  ...;
  sccp <= cn [label="SCCP Connection Confirm"];
  sccp abox sccp [label="MAP_SCCP_ST_CONNECTED"];
  --- [label="if SCCP CC with payload"];
  rua <= sccp [label="MAP_RUA_EV_TX_RANAP_MSG\ndata = ranap_msg"];
  hnb <= rua [label="RUA DirectTransfer"];

  ...;
  ...;
  --- [label="Layer 3 communication"];
  sccp <= cn [label="SCCP Data Form 1"];
  rua <= sccp [label="MAP_RUA_EV_TX_RANAP_MSG\ndata = ranap_msg"];
  hnb <= rua [label="RUA DirectTransfer"];
  ...;
  hnb => rua [label="RUA DirectTransfer"];
  rua => sccp [label="MAP_SCCP_EV_TX_RANAP_MSG\ndata = ranap_msg"];
  sccp => cn [label="SCCP Data Form 1"];

  ...;
  ...;
  --- [label="Usual release"];
  sccp <= cn [label="SCCP Data Form 1\nIu-ReleaseCommand"];
  rua <= sccp [label="MAP_RUA_EV_TX_RANAP_MSG\ndata = ranap_msg"];
  hnb <= rua [label="RUA DirectTransfer\nIu-ReleaseCommand"];
  ...;
  hnb => rua [label="RUA Disconnect\nIu-ReleaseComplete"];
  rua rbox rua [label="MAP_RUA_EV_RX_DISCONNECT"];
  rua abox rua [label="MAP_RUA_ST_DISCONNECTED"];
  rua => sccp [label="MAP_SCCP_EV_RAN_DISC\ndata = ranap_msg"];
  sccp => cn [label="SCCP Data Form 1\nIu-ReleaseComplete\nNOT 'SCCP Released'! See 3GPP TS 48.006 9.2"];
  sccp abox sccp [label="MAP_SCCP_ST_WAIT_RLSD"];
  ...;
  sccp <= cn [label="SCCP Released"];
  sccp abox sccp [label="MAP_SCCP_ST_DISCONNECTED"];
  rua rbox sccp [label="map_check_released()"];
  rua rbox sccp [label="hnbgw_context_map_free()"];

  ...;
  ...;
  --- [label="Ungraceful release from CN"];
  sccp <= cn [label="SCCP Released"];
  sccp => cn [label="SCCP Release Complete\n(implicit by libosmo-sigtran)"];
  sccp rbox sccp [label="MAP_SCCP_EV_RX_RELEASED"];
  sccp note sccp [label="In SCCP there is no \"link loss\".\nIn every case, we will be notified\nvia N-Disconnect prim per SCCP conn."];
  sccp abox sccp [label="MAP_SCCP_ST_DISCONNECTED"];
  rua <= sccp [label="MAP_RUA_EV_CN_DISC"];
  hnb <= rua [label="RUA Disconnect"];
  rua abox rua [label="MAP_RUA_ST_DISCONNECTED"];
  rua rbox sccp [label="map_check_released()"];
  rua rbox sccp [label="hnbgw_context_map_free()"];

  ...;
  ...;
  ...;
  --- [label="PCSTATE handling"];
  sccp << cn [label="N-PCSTATE.indication\npoint-code unreachable"];
  sccp note sccp [label="currently ignored"];

  ...;
  ...;
  --- [label="Ungraceful release from HNB"];
  hnb -x rua [label="link loss"];
  rua rbox rua [label="MAP_RUA_EV_HNB_LINK_LOST"];
  rua => sccp [label="MAP_SCCP_EV_RAN_DISC"];
  sccp => cn [label="SCCP Released"];
  sccp abox sccp [label="MAP_SCCP_ST_DISCONNECTED"];
  rua abox rua [label="MAP_RUA_ST_DISCONNECTED"];
  rua rbox sccp [label="map_check_released()"];
  rua rbox sccp [label="hnbgw_context_map_free()"];

  ...;
  ...;
  --- [label="Ungraceful release from HNB De-Register"];
  hnb => rua [label="HNBAP HNB De-Register"];
  --- [label="or"];
  hnb => rua [label="HNBAP HNB Register\n(HNB restarted)"];
  ---;
  rua rbox rua [label="MAP_RUA_EV_HNB_LINK_LOST"];
  hnb <= rua [label="RUA Disconnect"];
  hnb note rua [label="TODO: does it make sense to send\nRUA Disconnect per context when HNB is/was gone?\nOr has the HNB implicitly discarded these?"];
  rua abox rua [label="MAP_RUA_ST_DISCONNECTED"];
  rua => sccp [label="MAP_SCCP_EV_RAN_DISC\nfrom map_rua_disconnected_onenter()"];
  sccp abox sccp [label="MAP_SCCP_ST_WAIT_RLSD"];
  rua => sccp [label="MAP_SCCP_EV_RAN_DISC\nto skip waiting for SCCP Released from CN"];
  sccp => cn [label="SCCP Released"];
  sccp abox sccp [label="MAP_SCCP_ST_DISCONNECTED"];
  rua rbox sccp [label="map_check_released()"];
  rua rbox sccp [label="hnbgw_context_map_free()"];
}