Why call it “IMPLICIT” tagging”?

• If a TLV has the default tag, a dumb line-monitor knows the type of the value

• If a tag is overridden (IMPLICIT tagging) with an arbitrary tag, the tag only implies the type.

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The word “IMPLICIT” is quite meaningful - the tag no longer identifies the type, but rather implies it.

If only default tags are used, a dumb line-monitor examining the passing TLVs, can display each V part in an appropriate fashion (as a boolean, as n integer, or as a character string).

But if the tag has been overridden by “implicit tagging”, it needs to know the type definition (the new tag that has been used) to determine the type of the element - the tag only implies the type.