This may be appropriate when {HEAD ~ the availability information} depends on the specific communication unit which placed {TAIL ~ the request} or when such requests are relatively infrequent 
This may be appropriate when { HEAD ~ the availability information } depends on the specific communication unit which placed { TAIL ~ the request } or when such requests are relatively infrequent
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH