When the URL is available; initiating, using the URL, a first contact attempt with the communications unit; and contacting, using the URN, {HEAD ~ a home location register} to validate {TAIL ~ the URL} 
When the URL is available ; initiating , using the URL , a first contact attempt with the communications unit ; and contacting , using the URN , { HEAD ~ a home location register } to validate { TAIL ~ the URL }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL