267Network Topology and Implementation
The notion of a real-time protocol is that one asks the eld, what the value of input
238 is, and it replies what the value of input 238 is right now. There is no history.
During a denial of service attack, it is likely that one would lose and never be able to
retrieve data of what happened during the attack.
With event-oriented protocols such as DNP3, the actual interrogation is analo-
gous to “what’s new?” The remote device can reply not only what the current reading
is but also what it did in the past, or that not much has changed. A reply comparable
to the example above might say something like: Input 238 was 21323 at 12:02:03,
21400 at 12:03:23, and 22312 at 12:04:27. In effect, it includes the eve ...