2 ms·
The 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 r
by gumby 4y ago
The 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.
- smingo 4y agoSomeone must have felt very clever when they concluded Erlang would be dimensionless. Calls per second X seconds per call = no unit. But that's wrong. Clearly the number of calls ongoing maps on to lines being used for a circuit-switched network, or datagrams in flight, or whatever. Far from dimensionless. Call_starts per second X call.seconds per call_start = calls as the unit Much more plausible, IMHO.