Layer
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... For example, retrieving mail is a type of application service that
can be implemented by different application-layer protocols (e.g.,
POP3, IMAP4 ...
... domain to a specific server,
SRV records are limited to one layer of indirection and are focused
on server administration rather than on application naming.
Furthermore, although the DDDS ...
... host and port. The use cases described herein require an
additional layer -- from some service label to servers that may in be
hosted within different administrative domains ...