{HEAD ~ This request} may be originated by the user, by {TAIL ~ the system operator}, or by the subscriber identity module 
{ HEAD ~ This request } may be originated by the user , by { TAIL ~ the system operator } , or by the subscriber identity module
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH