Flash crowds and DOS on POTS

Mon May 17 14:20:28 UTC 2004

On Mon, 17 May 2004, Iljitsch van Beijnum wrote:

: > The difference is when people get a "busy" signal on the phone
: > network, they don't think phone network is collapsing.
:
: If they knew the difference between a busy signal and a congestion
: signal they probably would...

In the US, the busy signal and reorder signal use the same tone (combined
480+620 Hz), but the reorder signal sounds every half second instead of
every second.  Reorder is used in a failure situation that is not otherwise
handled -- typically because of a dead trunk, completely full outbound
trunks, or timeout during call setup.

Most folks don't have any idea what the reorder tone means.  It just sounds
like a "fast busy signal" to them, and is often confusing.  In real
overloaded congestion situations, most local and long distance providers do
use recordings with SIT tones that typically follow one of the wordings:

    All circuits are busy now.  Please try your call again later.

    Your call did not go through.  Please try your call again.

Where they can be used, most telcos prefer these to a reorder tone, as the
human voice makes the network seem less fragile to users.

On a tangent, a morbidly amusing recording from the AT&T long distance
network that I heard in June 1992 when trying to call a relative in Laguna
after a large earthquake hit California:

    Due to a natural disaster in the area you are calling, your call did not
    go through.  Will you please try your call again later.

-- 
-- Todd Vierling <tv at duh.org> <tv at pobox.com>