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I remember that outage. It was finally blamed (as described in this brief) on phone switch manufacturer DSC. IIRC this killed the company. Their SLA with the
by gumby 4y ago
I remember that outage. It was finally blamed (as described in this brief) on phone switch manufacturer DSC. IIRC this killed the company. Their SLA with their customers was something like three minutes of downtime per decade.
DSC was our customer at Cygnus. They were interesting as a customer (tough requirements but they paid a lot for them). For example if they reported a bug and got a fix they diffed the binaries and looked at every difference to be sure that the change was a result of the fix, and nothing else (no, they didn’t want upgrades).
- JosephRedfern 4y ago> For example if they reported a bug and got a fix they diffed the binaries and looked at every difference to be sure that the change was a result of the fix, and nothing else (no, they didn’t want upgrades). That sounds pretty diligent!
- yunohn 4y ago> Their SLA with their customers was something like three minutes of downtime per decade. That is insane. I really feel like modern SLAs are only getting worse - so much so that most companies fudge them, and try their hardest to never declare any sort of outage.
- wincy 4y agoWhat do you mean, Microsoft 358 is an excellent product that has uptime for exactly what they’ve got on the label!
- deleted 4y ago[deleted]
- gumby 4y agoThe Bell System standard was an extremely high Erlang number, which of course they strove to provide at the lowest cost which meant extremely high utilization rate on hardware which in turn meant extreme uptime (compare to the then contemporary PTT QoS even in major economies like France). This is also why the software itself was designed with so many internal defenses and what I would consider an “immune system”. I’ve never seen anything like it even on an aircraft control system. That is mentioned in passing in the brief article but is easily missed if you don’t know what it’s referring to. Most of what is done on the Internet at, say, “layer 5 or above” isn’t at all important so there’s no need for this level of SLA, but the actual backbone carriers do still carry SLAs at around that level. With packet switching it’s easier for them to provide than it was in the days of the 4ESS and 5ESS.
- vatys 4y ago> The Bell System standard was an extremely high Erlang number I wasn't aware of erlang the unit (measuring telephone circuit load) and at first thought this had something to do with the language. https://en.wikipedia.org/wiki/Erlang_(unit) https://en.wikipedia.org/wiki/Erlang_(unit)
- gumby 4y agoWell, they are related in that they are both telephony related: the language was an internal Ericsson language for building fast switches and such devices. I am always surprised (though I shouldn’t be) when I see it mentioned in a non-telecom context.
- 4y ago
- hexbus 4y agoAccording to a tech that actually applied tbe updates (Long Lines group in FB), “The DSC incident occurred in June 1991, unrelated to this AT&T incident.”
- gumby 4y agoThanks. It was reported otherwise in the news back then, but TBH I'd trust someone likely to have been the person responsible, or close to that person. (it might sound crazy these days to trust "someone on the Internet" but really: what's the incentive not to tell the truth about something like this?)