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