This is a read-only counter, in milliseconds, tracking the highest playout FIFO, or jitter buffer, delay reached during this voice call, and it locks at its maximum value after roughly two days rather than wrapping. An admin monitors this to catch worst-case jitter buffering spikes during a call, which is more informative for diagnosing intermittent network problems than an average delay figure alone. For example, a call with a normal average delay but a very high high-water mark would tell an admin the network experienced a brief but severe jitter spike at some point during the call.