This soft copy for use by IBM employees only.
Additional Information
The
The architecture of the expansion unit is similar to that of the IBM 8260:
•Each module contains CAP/CAD components to interface to the ATM backplane.
•The ATM backplane is fully passive and uses female connectors to improve availability.
•The ATM backplane is
Note
This means that the IBM 8260 ATM CPSW Module is not supported in the IBM 8285 Expansion Chassis, which also means that any
However, the architecture is different in several key ways:
•
•
The control point is in a separate module (the base unit) from the switch.
The control point shares a set of CAP/CAD components with the ATM ports.
3.2 Switching Fabric
As described above, there are two switching mechanisms used in the IBM 8285, depending on whether the base unit is operating with or without an expansion unit. The following sections describe in detail the switching mechanism in each case.
3.2.1 Switching in the IBM 8285
This section describes the switching mechanism in the IBM 8285.
Before going into further details about the switching function of the 8285 switch, it is necessary to understand the internal frame format it uses. This format is described below.
3.2.1.1 Internal Cell Format
The 8285 switch uses the same internal frame format, a
•
•
The ATM cell received from a port by the SFE.
The SFE calculates a header error check value and compares it to the HEC that arrived in the cell′s header.
•If no error is detected (the calculated and transmitted HEC values match), the SFE strips the HEC from the cell′s header and sends the resulting
ATM cell to the CAP/CAD.
