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This soft copy for use by IBM employees only.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
┌────────────────┬───────────────┬───────┬───────┬────────────────┐
│ TB │ TBE │LCBAul │ SB │ LCBAuh │ ─┐
├────────┬───────┴───────────────┼───────┴───────┼────────────────┤ │ RH (8 byte)
│ │ NBA │ F1 │ F2 │ ─┘
├────────┼───────────────┬───────┴───────────────┴───────┬─────┬──┤
│ GFC │ VPI │ VCI │ PT │CL│ ── ATM Header
├────────┴───────────────┴───────────────────────────────┴─────┴──┤ (4 byte: without HEC)
││
││
││
││
││
││
│ ATM payload (48 byte) │
││
││
││
││
││
││
├─────────────────────────────────────────────────────────────────┤
│ Future Use │
└─────────────────────────────────────────────────────────────────┘
TB: Target Blade
TBE: Target Blade Extension
LCBAul: Leaf Control Block Address up(inbound) lower port
LCBAuh: Leaf Control Block Address up(inbound) higher port
NBA: Next Buffer Address
F1: Format Field 1st
F2: Format Field 2nd
GFC: Generic Flow Control
VPI: Virtual Path Identifier
VCI: Virtual Channel Identifier
PT: Payload Type
CL: Cell Loss Priority
HEC: Header Error Control
Figure 11. Internal Cell Format of the IBM 8285 Nways ATM Workgroup Switch
3.2.1.2 Switching without the Switch Chip
When no expansion chassis is connected, the IBM 8285 Base Unit implements a
direct connection between CAD_up and CAD_down. This means that inbound
cells would undergo the following process:
1. The SFE_up strips the HEC from valid cells and forwards the cell to the
CAD_up.
2. The CAD_up prepares the internal cell and forwards it directly to the
CAD_down.
3. The CAD_down uses the RH information to determine which ports to forward
the cell to, strips the internal header, and forwards the 52-byte cell to the
SFE_down.
24 ATM Workgroup Solutions: Implementing the 8285 ATM Switch