freq[mac, ip]++
if (!seen_last[mac, ip] || ts > seen_last[mac, ip] ) seen_last[mac, ip] = ts
if (!seen_first[mac, ip] || ts < seen_first[mac, ip]) seen_first[mac, ip] = ts
freq[mac, ip]++
if (!seen_last[mac, ip] || ts > seen_last[mac, ip] ) seen_last[mac, ip] = ts
if (!seen_first[mac, ip] || ts < seen_first[mac, ip]) seen_first[mac, ip] = ts