When using ISDN as backup medium, the called ISDN terminal adapter (TA) should validate the caller's E.I64 address [Reference 18].
H.4.3.1 Kadar se ISDN uporablja kot rezervni medij v pripravljenosti, klicani terminalski adapter (TA) ISDN preveri in potrdi klicateljev naslov E.164 [Sklic 18].