What does cascade and drill through mean?
The Cascade / Cascading is the term used for describing the method for allowing the two or more participants to enter the conference as the single multipoint Control Unit (MCU) can support. Cascade is usually meant to connect 2 separate MCUs, where the second MCU is acting and it will treat as other participants.
The host MCU will send the joining MCU the processed data streams which are then distributed to it video conference participants. While Drill through is a term that is used to describe the acting of exploring or browsing items like folders, files, related components. Generally associated with drill down which you move horizontally between 2 items via a related link.
To drill though is in the case of two reports that are in a master / detail relation with each other and by clicking master item on the master report you reach the details of the clicked item on the detailed report.