doc/manuals/images/sgs-mo_sms_idle.msc

msc {
	hscale=2;
	UE, MME, VLR [label="MSC/VLR"], HSS [label="HSS/HLR"], SMSC;

	UE box HSS	[label="EPS/IMSI attach procedure"];
	...;
	UE box MME	[label="UE triggered Service Request"];
	UE => MME	[label="UL NAS Transport"];
	MME => VLR	[label="SGsAP UPLINK UNITDATA\n(CP-DATA/RP-DATA/TPDU)"];
	VLR => SMSC	[label="MAP/GSUP Forward SM"];
	MME <= VLR	[label="SGsAP DOWNLINK UNITDATA"];
	UE <= MME	[label="DL NAS Transport"];
	...;

	VLR <= SMSC	[label="Delivery Report"];
	MME <= VLR	[label="SGsAP DOWNLINK UNITDATA"];
	UE <= MME	[label="DL NAS Transport"];
	UE => MME	[label="UL NAS Transport"];
	MME => VLR	[label="SGsAP UPLINK UNITDATA"];
	MME <= VLR	[label="SGsAP RELEASE REQ"];
}