well-known

tunnettu, kuuluisa, nimekäs

tuttu familiar Familiar, famous, renowned or widely known.
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{{quote-magazine|year=2013|month=July-August|author=http://www.americanscientist.org/authors/detail/philip-j-bushnell Philip J. Bushnell
puhekieltä Generally recognised; reserved for some usual purpose.
1972, Vint Cerf, Jon Postel, RFC 322 - Well known socket numbers

We would like to catalog other sockets which are supposed to be well-known

If the call to this function fails, you can assume the SID was invalid — even if it's a well-known SID.

A common approach is for the server to accept messages at a well-known port.