MIB-I was lacking in that it did not distinguish between different types of transmission media. A new group, the Transmission group, is allocated for this purpose:
transmission OBJECT IDENTIFIER ::= { mib-2 10 }
When Internet-standard definitions for managing transmission media are defined, the transmission group is used to provide a prefix for the names of those objects.
Typically, such definitions reside in the experimental portion of the MIB until they are "proven", then as a part of the Internet standardization process, the definitions are accordingly elevated and a new object identifier, under the transmission group is defined. By convention, the name assigned is:
type OBJECT IDENTIFIER ::= { transmission number }
where "type" is the symbolic value used for the media in the ifType column of the ifTable object, and "number" is the actual integer value corresponding to the symbol.