Voip is a read-only Counter32 giving the number of Voice Over Internet Protocol (VoIP) frames counted for the monitored network; per the MIB a value of 4294967294 means the count is unknown rather than genuinely zero. Because it is broken out on its own instead of folded into a generic IP total, an admin can watch this counter to see how much of the monitored network's traffic is voice-call traffic, which is sensitive to latency and loss. If this Voip counter climbs sharply on the segment this probe watches while total traffic stays flat, that shift shows voice-call traffic, which is sensitive to latency and loss is displacing whatever other protocol mix was there before.