But in the IP world, there is a full continuum of states in between.
Some
of these are candidates for a useful service, and some of which aren't.
- Allowing a higher packet drop rate across all the "lower priority"
calls.
Note that this scenario gives so-called *IMPORTANT* traffic
the priority that is *DESIRED* while still allowing other
traffic to get through. In a disaster scenario like the
New Orleans hurricane, the official command and control
structure was not the sole organization doing useful work.
In such a chaotic scenario, common in war and in disasters,
it would be unwise to only have the option of shutting off
everybody else's service by preemption. The low priority
traffic could still be carrying mission critical messages
that are crucial to dealing with the disaster scenario.
This reminds me of an anecdote that a friend of mine recounted
some years ago. During the a war in some African country,
maybe Angola, the international phone lines were usually so
noisy that it was impossible for the embassy to hold a conversation
with their leaders back in Africa. Faxes were also virtually
impossible to transmit. He solved this problem by installing a
UUCP email system that communicated back to Africa using Telebit
PEP modems. Unlike other modems of the day, the PEP protocol
divided the potential bandwidth of the communications channel
into 256 frequency ranges, tested each range and used as many
ranges as were functional. This testing and choosing process was
repeated periodically so that as the noise pattern shifted, PEP
would search out the cleanest parts of the channel and use those.
The bursts of data that succeeded in reaching their destination
are analogous to packets and the channel seeking behaviour is
analogous to routing/failover.
The end result was a reliable email communications channel. It
could and often did take many minutes to transmit just a few
lines of text, but it did function and this allowed the embassy
to function where before they were paralyzed.
IP networks allow this same possibility, that of finding a low
bandwidth end-to-end path amidst a cacophony of cross-traffic.
The IETF should do some more education on how the existing
protocol set could be used in disaster/war scenarios without
needing any new features tacked on to it.
--Michael Dillon
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