diff --git a/ggsn_tests/GGSN_Tests.ttcn b/ggsn_tests/GGSN_Tests.ttcn
index 203dcbf..7f6f67c 100644
--- a/ggsn_tests/GGSN_Tests.ttcn
+++ b/ggsn_tests/GGSN_Tests.ttcn
@@ -39,6 +39,7 @@
 	const integer GTP1C_PORT := 2123;
 	const integer GTP1U_PORT := 2152;
 	const integer PCRF_PORT := 3868;
+	const integer OCS_PORT := 3869;
 
 	type enumerated GGSN_Impl {
 		GGSN_IMPL_OSMOCOM,
@@ -128,6 +129,10 @@
 		var DIAMETER_Emulation_CT vc_Gx;
 		port DIAMETER_PT Gx_UNIT;
 		port DIAMETEREM_PROC_PT Gx_PROC;
+		var DIAMETER_Emulation_CT vc_Gy;
+		port DIAMETER_PT Gy_UNIT;
+		port DIAMETEREM_PROC_PT Gy_PROC;
+		var integer g_gy_validity_time := 0; /* In seconds. 0 => disabled, !0 => grant over CC-Time period */
 	}
 
 	private function f_init_vty() runs on GT_CT {
@@ -203,7 +208,10 @@
 			unitdata_cb := refers(DiameterForwardUnitdataCallback),
 			raw := true /* handler mode (single component for all IMSI)) */
 		};
-		var DIAMETER_conn_parameters pars := {
+		var DIAMETER_conn_parameters pars;
+
+		/* Gx setup: */
+		pars := {
 			remote_ip := m_ggsn_ip_gtpc,
 			remote_sctp_port := -1,
 			local_ip := m_bind_ip_gtpc,
@@ -219,7 +227,25 @@
 		connect(vc_Gx:DIAMETER_PROC, self:Gx_PROC);
 		vc_Gx.start(DIAMETER_Emulation.main(ops, pars, id));
 
+		/* Gy setup: */
+		pars := {
+			remote_ip := m_ggsn_ip_gtpc,
+			remote_sctp_port := -1,
+			local_ip := m_bind_ip_gtpc,
+			local_sctp_port := OCS_PORT,
+			origin_host := "ocs.localdomain",
+			origin_realm := "localdomain",
+			auth_app_id := c_DIAMETER_CREDIT_CONTROL_AID,
+			vendor_app_id := omit
+		};
+		vc_Gy := DIAMETER_Emulation_CT.create(id);
+		map(vc_Gy:DIAMETER, system:DIAMETER_CODEC_PT);
+		connect(vc_Gy:DIAMETER_UNIT, self:Gy_UNIT);
+		connect(vc_Gy:DIAMETER_PROC, self:Gy_PROC);
+		vc_Gy.start(DIAMETER_Emulation.main(ops, pars, id));
+
 		f_diameter_wait_capability(Gx_UNIT);
+		f_diameter_wait_capability(Gy_UNIT);
 		/* Give some time for our emulation to get out of SUSPECT list of SUT (3 watchdong ping-pongs):
 		 * RFC6733 sec 5.1
 		 * RFC3539 sec 3.4.1 [5]
@@ -425,9 +451,9 @@
 		}
 	}
 
-	private altstep as_DIA_CCR(DCC_NONE_CC_Request_Type req_type) runs on GT_CT {
+	private altstep as_DIA_Gx_CCR(DCC_NONE_CC_Request_Type req_type) runs on GT_CT {
 		var PDU_DIAMETER rx_dia;
-		[] Gx_UNIT.receive(tr_DIA_CCR(req_type := req_type)) -> value rx_dia {
+		[] Gx_UNIT.receive(tr_DIA_Gx_CCR(req_type := req_type)) -> value rx_dia {
 			var template (omit) AVP avp;
 			var octetstring sess_id;
 			var AVP_Unsigned32 req_num;
@@ -438,7 +464,7 @@
 			avp := f_DIAMETER_get_avp(rx_dia, c_AVP_Code_DCC_NONE_CC_Request_Number);
 			req_num := valueof(avp.avp_data.avp_DCC_NONE_CC_Request_Number);
 
-			Gx_UNIT.send(ts_DIA_CCA(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
+			Gx_UNIT.send(ts_DIA_Gx_CCA(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
 						 req_type, req_num));
 		}
 		[] Gx_UNIT.receive(PDU_DIAMETER:?) -> value rx_dia {
@@ -447,6 +473,34 @@
 		}
 	}
 
+	private altstep as_DIA_Gy_CCR(DCC_NONE_CC_Request_Type req_type) runs on GT_CT {
+		var PDU_DIAMETER rx_dia;
+		[] Gy_UNIT.receive(tr_DIA_Gy_CCR(req_type := req_type)) -> value rx_dia {
+			var template (value) PDU_DIAMETER tx_dia;
+			var template (omit) AVP avp;
+			var octetstring sess_id;
+			var AVP_Unsigned32 req_num;
+
+			avp := f_DIAMETER_get_avp(rx_dia, c_AVP_Code_BASE_NONE_Session_Id);
+			sess_id := valueof(avp.avp_data.avp_BASE_NONE_Session_Id);
+
+			avp := f_DIAMETER_get_avp(rx_dia, c_AVP_Code_DCC_NONE_CC_Request_Number);
+			req_num := valueof(avp.avp_data.avp_DCC_NONE_CC_Request_Number);
+			if (g_gy_validity_time > 0) {
+				tx_dia := ts_DIA_Gy_CCA_ValidityTime(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
+							 req_type, req_num, g_gy_validity_time);
+			} else {
+				tx_dia := ts_DIA_Gy_CCA(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
+							 req_type, req_num);
+			}
+			Gy_UNIT.send(tx_dia);
+		}
+		[] Gy_UNIT.receive(PDU_DIAMETER:?) -> value rx_dia {
+			Misc_Helpers.f_shutdown(__BFILE__, __LINE__, fail,
+						log2str("Received unexpected DIAMETER Gy", rx_dia));
+		}
+	}
+
 	/* send a PDP context activation */
 	function f_pdp_ctx_act(inout PdpContext ctx, template OCT1 exp_cause := '80'O) runs on GT_CT return CreatePDPContextResponse {
 		var Gtp1cUnitdata ud;
@@ -460,7 +514,10 @@
 		T_default.start;
 		d := activate(pingpong());
 		if (Gx_PROC.checkstate("Connected")) {
-			as_DIA_CCR(INITIAL_REQUEST);
+			as_DIA_Gx_CCR(INITIAL_REQUEST);
+		}
+		if (Gy_PROC.checkstate("Connected")) {
+			as_DIA_Gy_CCR(INITIAL_REQUEST);
 		}
 		alt {
 			[] GTPC.receive(tr_GTPC_MsgType(g_peer_c, createPDPContextResponse, ctx.teic)) -> value ud {
@@ -522,7 +579,10 @@
 		T_default.start;
 		d := activate(pingpong());
 		if (Gx_PROC.checkstate("Connected") and expect_diameter) {
-			as_DIA_CCR(TERMINATION_REQUEST);
+			as_DIA_Gx_CCR(TERMINATION_REQUEST);
+		}
+		if (Gy_PROC.checkstate("Connected") and expect_diameter) {
+			as_DIA_Gy_CCR(TERMINATION_REQUEST);
 		}
 		alt {
 			[] GTPC.receive(tr_GTPC_MsgType(g_peer_c, deletePDPContextResponse, expect_teid)) -> value ud {
@@ -1938,7 +1998,8 @@
 
 		T_next.start;
 		alt {
-		[Gx_PROC.checkstate("Connected")] as_DIA_CCR(INITIAL_REQUEST) { repeat; }
+		[Gx_PROC.checkstate("Connected")] as_DIA_Gx_CCR(INITIAL_REQUEST) { repeat; }
+		[Gy_PROC.checkstate("Connected")] as_DIA_Gy_CCR(INITIAL_REQUEST) { repeat; }
 		[] pingpong();
 		[] T_next.timeout {
 			f_send_gtpc(ts_GTPC_CreatePDP(g_peer_c, g_c_seq_nr, ctx[next_req_ctx].imsi, g_restart_ctr,
@@ -1992,7 +2053,8 @@
 		rx_resp_ctx := 0;
 		T_next.start;
 		alt {
-		[Gx_PROC.checkstate("Connected")] as_DIA_CCR(TERMINATION_REQUEST) { repeat; }
+		[Gx_PROC.checkstate("Connected")] as_DIA_Gx_CCR(TERMINATION_REQUEST) { repeat; }
+		[Gy_PROC.checkstate("Connected")] as_DIA_Gy_CCR(TERMINATION_REQUEST) { repeat; }
 		[] pingpong();
 		[] T_next.timeout {
 			f_send_gtpc(ts_GTPC_DeletePDP(g_peer_c, g_c_seq_nr, ctx[next_req_ctx].teic_remote, ctx[next_req_ctx].nsapi, '1'B));
@@ -2044,7 +2106,8 @@
 
 		T_next.start;
 		alt {
-		[Gx_PROC.checkstate("Connected")] as_DIA_CCR(INITIAL_REQUEST) { repeat; }
+		[Gx_PROC.checkstate("Connected")] as_DIA_Gx_CCR(INITIAL_REQUEST) { repeat; }
+		[Gy_PROC.checkstate("Connected")] as_DIA_Gy_CCR(INITIAL_REQUEST) { repeat; }
 		[] pingpong();
 		[] T_next.timeout {
 			if (cont_req) {
@@ -2093,7 +2156,7 @@
 		rx_resp_ctx := 0;
 		T_next.start;
 		alt {
-		[Gx_PROC.checkstate("Connected")] as_DIA_CCR(TERMINATION_REQUEST) { repeat; }
+		[Gx_PROC.checkstate("Connected")] as_DIA_Gx_CCR(TERMINATION_REQUEST) { repeat; }
 		[] pingpong();
 		[] T_next.timeout {
 			f_send_gtpc(ts_GTPC_DeletePDP(g_peer_c, g_c_seq_nr, teic_list[next_req_ctx], '0001'B, '1'B));
@@ -2124,6 +2187,56 @@
 		f_shutdown_helper();
 	}
 
+	/* Test charging over Gy interface. */
+	testcase TC_gy_charging_cc_time() runs on GT_CT {
+		var default d;
+
+		g_gy_validity_time := 3; /* Grant access for 3 seconds, needs to be re-validated afterwards */
+		f_init();
+		var PdpContext ctx := valueof(t_DefinePDP(f_rnd_imsi('26242'H), '1234'O, c_ApnInternet, valueof(t_EuaIPv4Dyn)));
+		ctx.pco_req := valueof(ts_PCO_IPv4_DNS_CONT);
+		f_pdp_ctx_act(ctx);
+
+		var OCT4 dns1_addr := f_PCO_extract_proto(ctx.pco_neg, '000d'O);
+
+		/* Send some UL traffic: */
+		var OCT4 saddr := ctx.eua.endUserAddress.endUserAddressIPv4.ipv4_address;
+		f_send_gtpu(ctx, f_gen_icmpv4_echo(saddr, dns1_addr));
+		f_wait_icmp4_echo_reply(ctx);
+
+		T_default.start(10.0);
+		d := activate(pingpong());
+
+		g_gy_validity_time := 2;
+		/* First update reports octests/pkt on both UL/DL (see icmp ping-pong above) */
+		as_DIA_Gy_CCR(UPDATE_REQUEST);
+
+		/* Second update: 0 ul/dl pkt/octet should be reported, since nothing was sent */
+		as_DIA_Gy_CCR(UPDATE_REQUEST);
+
+		/* Third update: make sure report contains again octets/pkts for both UL/DL: */
+		f_send_gtpu(ctx, f_gen_icmpv4_echo(saddr, dns1_addr));
+		f_wait_icmp4_echo_reply(ctx);
+		f_send_gtpu(ctx, f_gen_icmpv4_echo(saddr, dns1_addr));
+		f_wait_icmp4_echo_reply(ctx);
+		as_DIA_Gy_CCR(UPDATE_REQUEST);
+
+		/* Let the CCA reach the GGSN */
+		f_sleep(0.5);
+		deactivate(d);
+		T_default.stop;
+
+		/* Send some data and validate it is reported in the TERMINATION_REQUEST
+		 * (triggered by PFCP Session Deletion Response): */
+		f_send_gtpu(ctx, f_gen_icmpv4_echo(saddr, dns1_addr));
+		f_wait_icmp4_echo_reply(ctx);
+
+		f_pdp_ctx_del(ctx, '1'B);
+
+
+		f_shutdown_helper();
+	}
+
 	control {
 		execute(TC_pdp4_act_deact());
 		execute(TC_pdp4_act_deact_ipcp());
@@ -2170,5 +2283,10 @@
 		execute(TC_lots_of_concurrent_pdp_ctx());
 		/* Keep at the end, crashes older osmo-ggsn versions (OS#5469): */
 		execute(TC_addr_pool_exhaustion());
+
+		/* open5gs specific tests: */
+		if (m_ggsn_impl == GGSN_IMPL_OPEN5GS) {
+			execute(TC_gy_charging_cc_time());
+		}
 	}
 }
diff --git a/library/DIAMETER_Templates.ttcn b/library/DIAMETER_Templates.ttcn
index f7244d8..24b9cd8 100644
--- a/library/DIAMETER_Templates.ttcn
+++ b/library/DIAMETER_Templates.ttcn
@@ -100,6 +100,8 @@
 	DIAMETER_ERROR_EAP_CODE_UNKNOWN			(5048)
 };
 
+/* Gy : 3GPP TS 32.299 7.1.6, RFC4006 3.1 */
+const uint32_t c_DIAMETER_CREDIT_CONTROL_AID := 4;
 /* 3GPP TS 29.272 Section 7.1.8 */
 const uint32_t c_DIAMETER_3GPP_Gx_AID := 16777238;
 const uint32_t c_DIAMETER_3GPP_S6_AID := 16777251;
@@ -860,6 +862,56 @@
 	}
 }
 
+/* RFC4006 8.16 Multiple-Services-Credit-Control AVP */
+template (value) GenericAVP ts_AVP_Multiple_Services_Credit_Control(template (value) AVP_list content) := {
+	avp := {
+		avp_header := ts_DIA_Hdr(c_AVP_Code_DCC_NONE_Multiple_Services_Credit_Control),
+		avp_data := {
+			avp_DCC_NONE_Multiple_Services_Credit_Control := content
+		}
+	}
+}
+
+/* RFC4006 8.17 Granted-Service-Unit AVP */
+template (value) GenericAVP ts_AVP_Granted_Service_Unit(template (value) AVP_list content) := {
+	avp := {
+		avp_header := ts_DIA_Hdr(c_AVP_Code_DCC_NONE_Granted_Service_Unit),
+		avp_data := {
+			avp_DCC_NONE_Granted_Service_Unit := content
+		}
+	}
+}
+
+/* RFC4006 8.21 CC-Time AVP */
+template (value) GenericAVP ts_AVP_CC_Time(uint32_t cc_time_val) := {
+	avp := {
+		avp_header := ts_DIA_Hdr(c_AVP_Code_DCC_NONE_CC_Time),
+		avp_data := {
+			avp_DCC_NONE_CC_Time := int2oct(cc_time_val, 4)
+		}
+	}
+}
+
+/* RFC4006 8.23 CC-Total-Octets AVP */
+template (value) GenericAVP ts_AVP_CC_Total_Octets(uint64_t cc_total_octets_val) := {
+	avp := {
+		avp_header := ts_DIA_Hdr(c_AVP_Code_DCC_NONE_CC_Total_Octets),
+		avp_data := {
+			avp_DCC_NONE_CC_Total_Octets := int2oct(cc_total_octets_val, 8)
+		}
+	}
+}
+
+/* RFC4006 8.33 Validity-Time AVP */
+template (value) GenericAVP ts_AVP_Validity_Time(uint32_t validity_time_val) := {
+	avp := {
+		avp_header := ts_DIA_Hdr(c_AVP_Code_DCC_NONE_Validity_Time),
+		avp_data := {
+			avp_DCC_NONE_Validity_Time := int2oct(validity_time_val, 4)
+		}
+	}
+}
+
 
 
 /* 5.3.2 Capabilities Exchange Answer */
@@ -1101,7 +1153,7 @@
 
 /* RFC 4006 3.1.  Credit-Control-Request (CCR) Command */
 template (present) PDU_DIAMETER
-tr_DIA_CCR(template (present) DCC_NONE_CC_Request_Type req_type := INITIAL_REQUEST)
+tr_DIA_Gx_CCR(template (present) DCC_NONE_CC_Request_Type req_type := INITIAL_REQUEST)
 := tr_DIAMETER(flags:='11000000'B, cmd_code:=Credit_Control,
 			    app_id:=int2oct(c_DIAMETER_3GPP_Gx_AID, 4),
 	avps := superset(
@@ -1113,15 +1165,28 @@
 		tr_AVP_CcReqType(req_type),
 		tr_AVP_CcReqNum(?)
 	));
+template (present) PDU_DIAMETER
+tr_DIA_Gy_CCR(template (present) DCC_NONE_CC_Request_Type req_type := INITIAL_REQUEST)
+:= tr_DIAMETER(flags:='11000000'B, cmd_code:=Credit_Control,
+			    app_id:=int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4),
+	avps := superset(
+		tr_AVP_SessionId,
+		tr_AVP_OriginHost,
+		tr_AVP_OriginRealm,
+		tr_AVP_DestinationRealm,
+		tr_AVP_AuthAppId(int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4)),
+		tr_AVP_CcReqType(req_type),
+		tr_AVP_CcReqNum(?)
+	));
+
 
 
 /* RFC 4006 3.2.  Credit-Control-Answer (CCA) Command */
 template (value) PDU_DIAMETER
-ts_DIA_CCA(template (value) UINT32 hbh_id, template (value) UINT32 ete_id,
+ts_DIA_Gx_CCA(template (value) UINT32 hbh_id, template (value) UINT32 ete_id,
 	   template (value) octetstring sess_id,
 	   template (value) DCC_NONE_CC_Request_Type req_type,
 	   template (value) AVP_Unsigned32 req_num)
-
 := ts_DIAMETER(flags:='01000000'B, cmd_code:=Credit_Control,
 		app_id:=int2oct(c_DIAMETER_3GPP_Gx_AID, 4), hbh_id:=hbh_id, ete_id:=ete_id,
 	avps := {
@@ -1137,6 +1202,56 @@
 		// supported features
 		// origin
 	});
+template (value) PDU_DIAMETER
+ts_DIA_Gy_CCA(template (value) UINT32 hbh_id, template (value) UINT32 ete_id,
+	   template (value) octetstring sess_id,
+	   template (value) DCC_NONE_CC_Request_Type req_type,
+	   template (value) AVP_Unsigned32 req_num)
+:= ts_DIAMETER(flags:='01000000'B, cmd_code:=Credit_Control,
+		app_id:=int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4), hbh_id:=hbh_id, ete_id:=ete_id,
+	avps := {
+		ts_AVP_SessionId(sess_id),
+		ts_AVP_ResultCode(DIAMETER_SUCCESS),
+		ts_AVP_OriginHost("ocs.localdomain"),
+		ts_AVP_OriginRealm("localdomain"),
+		ts_AVP_AuthAppId(int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4)),
+		ts_AVP_CcReqType(req_type),
+		ts_AVP_CcReqNum(req_num)//,
+		// qos
+		// default eps bearer qos
+		// supported features
+		// origin
+	});
+/* Same as ts_DIA_Gy_CCA, but with extra AVP to grant access for limited amount of seconds */
+template (value) PDU_DIAMETER
+ts_DIA_Gy_CCA_ValidityTime(template (value) UINT32 hbh_id, template (value) UINT32 ete_id,
+	   template (value) octetstring sess_id,
+	   template (value) DCC_NONE_CC_Request_Type req_type,
+	   template (value) AVP_Unsigned32 req_num,
+	   uint32_t validity_time)
+:= ts_DIAMETER(flags:='01000000'B, cmd_code:=Credit_Control,
+		app_id:=int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4), hbh_id:=hbh_id, ete_id:=ete_id,
+	avps := {
+		ts_AVP_SessionId(sess_id),
+		ts_AVP_ResultCode(DIAMETER_SUCCESS),
+		ts_AVP_OriginHost("ocs.localdomain"),
+		ts_AVP_OriginRealm("localdomain"),
+		ts_AVP_AuthAppId(int2oct(c_DIAMETER_CREDIT_CONTROL_AID, 4)),
+		ts_AVP_CcReqType(req_type),
+		ts_AVP_CcReqNum(req_num),
+		ts_AVP_Multiple_Services_Credit_Control({
+			ts_AVP_Validity_Time(validity_time),
+			ts_AVP_Granted_Service_Unit({
+				//ts_AVP_CC_Time(validity_time*2),
+				ts_AVP_CC_Total_Octets(1000)
+				})
+			})
+		//,
+		// qos
+		// default eps bearer qos
+		// supported features
+		// origin
+	});
 
 /* RFC 6733, section 5.5.1 "Device-Watchdog-Request" */
 template (value) PDU_DIAMETER
diff --git a/library/Osmocom_Types.ttcn b/library/Osmocom_Types.ttcn
index 472b389..b698a2e 100644
--- a/library/Osmocom_Types.ttcn
+++ b/library/Osmocom_Types.ttcn
@@ -16,6 +16,7 @@
 type integer uint16_t (0..65535) with { variant "unsigned 16 bit" };
 type integer uint24_t (0..16777215) with { variant "unsigned 24 bit" };
 type integer uint32_t (0..4294967295) with { variant "unsigned 32 bit" };
+type integer uint64_t (0..18446744073709551615) with { variant "unsigned 64 bit" };
 
 type integer int8_t (-128..127) with { variant "8 bit" };
 type integer int16_t (-32768..32767) with { variant "16 bit" };
diff --git a/pgw/PGW_Tests.ttcn b/pgw/PGW_Tests.ttcn
index a65ca43..9846dab 100644
--- a/pgw/PGW_Tests.ttcn
+++ b/pgw/PGW_Tests.ttcn
@@ -221,7 +221,7 @@
 
 private altstep as_DIA_CCR(DCC_NONE_CC_Request_Type req_type) runs on PGW_Session_CT {
 	var PDU_DIAMETER rx_dia;
-	[] DIAMETER.receive(tr_DIA_CCR(req_type := req_type)) -> value rx_dia {
+	[] DIAMETER.receive(tr_DIA_Gx_CCR(req_type := req_type)) -> value rx_dia {
 		var template (omit) AVP avp;
 		var octetstring sess_id;
 		var AVP_Unsigned32 req_num;
@@ -232,7 +232,7 @@
 		avp := f_DIAMETER_get_avp(rx_dia, c_AVP_Code_DCC_NONE_CC_Request_Number);
 		req_num := valueof(avp.avp_data.avp_DCC_NONE_CC_Request_Number);
 
-		DIAMETER.send(ts_DIA_CCA(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
+		DIAMETER.send(ts_DIA_Gx_CCA(rx_dia.hop_by_hop_id, rx_dia.end_to_end_id, sess_id,
 					 req_type, req_num));
 	}
 	[] DIAMETER.receive(PDU_DIAMETER:?) -> value rx_dia {