doc/manuals/images/sgs-imsi_attach_lu.msc

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

	UE => MME [label="Attach Request"];
	UE box HSS [label="Steps 3..16 of LTE Attach procedure TS 23.401"];
	MME box MME [label="Derive VLR Number"];
	MME => VLR [label="LU Request"];
	VLR box VLR [label="Create SGs Association"];
	VLR box HSS [label="MAP/GSUP UL / ISD"];
	MME <= VLR [label="LU Accept"];
	UE box HSS [label="Steps 17..16 of LTE Attach procedure TS 23.401"];
	|||;
	...;
	MME <= VLR [label="Paging Request"];
}