IBM SG24-4817-00 User Manual
Page 40
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 I B M 8285 Nways A T M 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