原创 Do you still see erlangs?

I was reading a technical-review article the other day and saw the word "erlangs." All I could think was, "wow, I haven't seen that word in a while!" Back in the day, if you were involved at all with telecommunications, system analysis, or telephony (another fading term, BTW), you knew about erlangs.

"What's an erlang, anyway?" you're asking. To quote from this site, "an Erlang is a unit of telecommunications traffic measurement. Strictly speaking, an Erlang represents the continuous use of one voice path.ÿIn practice, it is used to describe the total traffic volume of one hour."

The erlang parameter is based on the idea of a circuit-switched network, with a physical line dedicated to the voice call in progress. By knowing how many erlangs of traffic you had, you could determine how many physical circuit lines you needed in a phone system, whether to serve a business office, or a phone company central office, or for trunk lines between central offices. There are tables and formulas which showed resources needed to provide different thresholds of system availability, for any given number of erlangs of voice traffic.

Things have certainly changed. A dedicated circuit line for a voice call is largely an anachronism, as we now digitize voice, break the resultant data streams into packets, and route them via a packet-switching network. We think of system capacity in terms of bandwidth, data rates, bit error rate, throughput, and other parameters—not erlangs.

So the erlang, which served the industry well and was the basis for so much system design and provisioning, has dimmed severely in the lexicon of the telecom engineer. That's how things go in our high-tech world: for a while, you're vital; later on, you're perhaps just a footnote.

Are there any technical terms that you used to see, but no longer do? Are there terms you see which wished you knew what they were about, and why they were used?