This soft copy for use by IBM employees only.
The CAD function prepares the cell for transmission to the switch. The CAD builds the internal cell in its RAM according to instructions given by the CAP.
As described in 3.1, ªIBM 8285 Architecture Overviewº on page17, the IBM 8285 base unit is treated as a single module and all ports in the base unit share two sets of CAP/CAD, one set to handle the inbound cells, called CAP_up and CAD_up, and the other set to handle the outbound cells, called CAP_down and CAD_down.
•SFE (Specific Front End)
The SFE handles the ATM
There are three sets of SFE components in the base unit: an inbound/outbound pair for the ATM25 ports, called HS.SFE_up/HS.SFE_down, an inbound/outbound pair for the ATM155 port, called SFE_up/SFE_down, and a single, bidirectional SFE used by the control point, called the CP SFE.
In addition, each ATM module also uses CAP, CAD, and SFE components, but in two sets: an inbound set (CAP_Up, CAD_Up, and SFE_Up), and an outbound set (CAP_Down, CAD_Down, and SFE_Down). Note that this slightly different from the 8285 switch which has the additional CP SFE, and which connects CAD_up directly to CAD_down when operating without an expansion unit.
