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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