The hash values for {HEAD ~ the connections} detected during {TAIL ~ the predetermined time period} preceding the current time period are stored in the second table 
detected during
The hash values for { HEAD ~ the connections } detected during { TAIL ~ the predetermined time period } preceding the current time period are stored in the second table
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH