# File lib/snmp/pdu.rb, line 275
    def trap_oid
        varbind = @varbind_list[1]
        if varbind && (varbind.name == SNMP_TRAP_OID_OID)
            return varbind.value
        else
            raise InvalidTrapVarbind, "Expected snmpTrapOID.0, found " + varbind.to_s 
        end
    end