IBM Power Systems 775 Manual page 134

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CAU
Figure 2-5 HFI attachment to neighboring devices
Packet processing
Serving as the interface between POWER7 chip quads and the cluster network, the HFI
moves data between PowerBus and the Integrated Switch Router (ISR). The data is in
packets of varying formats, but all packets are processed in the following manner:
Sending:
– Pulls or receives data from PowerBus-attached devices in a POWER7 chip
– Translates data into network packets
– Injects network packets into the cluster network via the ISR
Receiving:
– Receives network packets from the cluster network via the ISR
– Translates the packets into transactions
– Pushes the transactions to PowerBus-attached devices in a POWER7 chip
Packet ordering
The HFIs and cluster network provide no ordering guarantees among packets. Packets
that are sent from the same source window and node to the same destination window and
node might reach that destination in a different order.
Figure 2-6 on page 121 shows two HFIs cooperating to move data from devices attached to
one PowerBus to devices that are attached to another PowerBus through the cluster network.
120
IBM Power Systems 775 for AIX and Linux HPC Solution
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