IBM SG24-4817-00 manual This soft copy for use by IBM employees only

This soft copy for use by IBM employees only.

•The CAP/CAD adds a 2-byte internal header (called a routing header (RH)), and 1-byte trailer.

The RH contains the information necessary to route the internal cell. Basically, the switching information is contained in the Source Blade (SB) and Target Blade (TB) fields, which correspond to ports on the

switch-on-a-chip, and which the switch uses in order forward the cell to the correct blade(s). The switch itself does not use destination port or VPC/VCC number when switching the cell. However, at the module level, the CAP/CAD would forward the cell to the appropriate port(s) based on the target port (TP) contained in the format field of the RH.

Note: In this context, blade refers to the set of components that share a common CAP/CAD. This is normally a module, such as an ATM media module or the ATM Control Point and Switch module of the IBM 8260. However, by this definition, the IBM 8285 Base Unit can be considered a blade or module as well, since its ports share a common CAP/CAD.

Figure 11 on page 24 shows the internal cell format used in the IBM 8285. Note the internal cell format will be changed in future releases but the concept should remain similar and able to be referenced.

Chapter 3. Functional Overview of the IBM 8285 23