Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-36
Multi-CPU Routing Examples
Combination 1: Local Source Node and Neighbor
Destination Node
In this scenario, the source node is the local node and the destination node is a
neighbor; a message is sent directly from one node to the other. When the first
message destined for each processor in the neighbor node is sent, the originating
processor selects a local path to the destination node and selects a pair of Expand
line-handlers for the source and destination processor combination. Subsequent
messages from that originating processor to that destination processor use the same
path.
For example, in Figure 18-11, if the process named PRCB on node \B sends a
message to the process named PRCC on node \C and $NCP determines that multi-
CPU path 1 is the best-path route, the NRT in processor 0 selects the Expand line-
handler process in processor 2 to transmit the message because its remote Expand
line-handler process is in the same processor as PRCC.
If PRCB (or any other process in processor 0 on node \B) sends another message to
PRCC (or any other process in processor 1 on node \C), $NCP immediately uses the
same Expand line-handler to transmit the message, this time because an Expand line-
handler pairing has been initiated.
Combination 2: Local Source Node and Non-Neighbor
Destination Node
In this scenario, the source node is the local node and the destination node is a non-
neighbor node. An Expand line-handler process is selected by $NCP when the
connection between the nodes is first established and all processors in the system use
this Expand line-handler process.
For example, in Figure 18-11, when $NCP on node \B first detects the existence of
node \F and determines that the best-path route to node \F is through the multi-CPU
path 1, $NCP selects an Expand line-handler process from one of those on processors
1, 2, or 4 based on the communications load and then updates the NRT in all
processors in the system. If the process named PRCB on node \B (or any other
process on node \B) sends a message to the process named PRCF on node \F (or any
other process on node \F), the NRT in processor 0 returns the Expand line-handler
process selected by $NCP, regardless of the current communications load.
Combination 3: Passthrough Traffic to a Neighbor
Destination Node
In this scenario, a message is received that is destined for a neighbor node connected
by a multi-CPU path. The message is routed to the Expand line-handler process
specified by the reverse pairing table (RPT)—if one exists. The RPT is established
when the neighbor connects to the originator of the passthrough message. The
Connect Request, Reply, and Ack messages are forward by $NCP, which sets the RPT