On 5/21/07, Yoz Grahame <[email protected]> wrote:
On 5/20/07, Matt McLeod <[email protected]> wrote:
> SMS is unreliable the way UDP or email is unreliable.
Um, aren't those two completely different classes of unreliability?
Email is unreliable due to shitty implementations of a reliable
protocol, whereas UDP is unreliable by design. (Unless this definition
of "unreliable" also includes "no guarantee of immediate delivery",
which would cover email)
SMS has both. No guarantee of delivery at all (UDP), no guarantee of
timeliness either (SMTP). At least with UDP you either get it quickly
or not at all, with email you're guaranteed to get it (or the sender
gets a response saying why not) but it might take a week. SMS, maybe
you get it, maybe you don't, could take a while in any event.
Most of the time delivery works and is reasonably quick, hence people
using it for things it wasn't built for. Bit like people using Excel
as a database but with nastier consequences.
> Mostly it works
> but there's no guarantee. I wouldn't use it for critical alert
> systems unless the alternatives were even worse, which AFAIK is not
> the case in my particular part of the world.
I have heard of parts of America where it's used to send missions to
air ambulance crews. I heard this from someone who was, at the time, a
sysadmin for the telco which was providing the SMS network for these
ambulances, which they had no idea about until they accidentally saw
some of the messages queued during an accidental downtime. They put a
little more effort into their downtime response after that.
I worked for a vendor-to-telcos some years ago. Saw a leaked email
from a major customer, roughly "if the vendor meets the contract
target our SMS system won't cope, but it doesn't matter because they
won't get even halfway there". Naturally when we saw that all the
stops were pulled out to make sure we met the target.
Anyone using SMS for anything genuinely critical is an idiot. It may
be that your machines keeling over isn't critical enough for it to
matter (it isn't for us) but ambluance crews? That one definitely
rates but it'll probably take a lawsuit after someone dies to correct
it.
Matt
