awk -v bin_size=${1:-5} '
    # use a function so we can call as we process input and at the end without duplicating the code
    function dump( )                # dump out the information that we collected about the last bin
    {
        if( NR == 1 )               # we will call this for the first record; 
            return;                 # if this is the first record (NR equals 1) then we skip the print

        new_count = 0;
        for( u in unique )              # look at each unique IP we saved
            if( last_bin[u] == 0 )      # if it wasnt noticed last time, count it
                new_count++;

        bin++;
        printf( "%3d %3d %3d\n", bin, total, new_count );       # print all of the counts
    }

    {                                   # process for each record in the file (impled true condition)
        if( $1+0 >= next_bin )          # if timestamp (col 1) is in the next bin
        {
            dump( );                    # print data from the previous bin
            next_bin = $1 + bin_size;   # mark the start of the next bin

            delete last_bin;            # must delete contents of last bin
            for( u in unique )          # copy hits from this bin 
                last_bin[u] = 1;        # for comparison when we see the start of next bin
            delete unique;              # must delete the list of unique IPs from the current bin before we start
            total = 0;                  # zero number of hits in the bin
        }

        unique[$2]++                    # count the number of times this IP address was seen in the bin
        total++;                        # total number of entries in the bin
    }

    END {               # at the end of the file, one last print if we saw something in the previous bin
        if( total )
            dump( );
    }
'