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.
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.
I wasn't aware of erlang the unit (measuring telephone circuit load) and at first thought this had something to do with the language.
Calls per second X seconds per call = no unit.
Call_starts per second X call.seconds per call_start = calls as the unit
As a result, five or six nines availability is pretty standard. Six nines means you can lose no more than 31 seconds a year. As a result, traditional telco had all kinds of cool tech in it, eg the Nortel DMS had live code patching as early as 1990 iirc.
At one time I worked at a vendor of IP telco switches, aiming to replace the legacy Nortel and Lucent with smaller tech. We had to learn some very, very hard lessons about reliability, but we eventually got there.
Today, I see cloud hyperscalers claiming that can run telco workloads, but I remain pretty skeptical until they can prove that they can switch a call, mid stream, from one node to another, without losing the audio, while transcoding it from one codec to another. Im not saying that public cloud needs to make the same tech choices re resilience, but today's web tech absolutely will not cut it.
The thing is, traditional telco can't do it anymore either. CenturyLink (aka Lumen) has broken 911 at least twice since 2018 when I moved into their territory. I've got the county emergency dispatch center in my address book, cause chances are, they'll do it a couple more times.
Networking is the last bastion of SLAs that actually seem to matter.