The ifIndex of the peer associated ifEntry. The ifIndex
appears after the associated ifEntry is created
successfully.
This ifIndex will be used to access the objects in the
Voice over Telephony or Voice over IP peer specific table.
In addition, the ifIndex is also used to access the
associated peer configuration entry of the IETF Dial
Control MIB. If the peer associated ifEntry had not been
created, then this object has a value of zero.