Open System Services Management and Operations Guide (G06.30+, H06.08+, J06.03+)

Figure 5 OSS AF_INET Sockets Servers for NonStop TCP/IP
The application processes (Processes 1 through 4) communicate with each other through the
transport-provider ($ZTCn) processes, with data being carried back and forth by the
transport-agent processes. Transport-agent processes do not communicate with each other
directly, but through the transport-provider.
NOTE: Whenever any application process sends a message to another process, the message
is always sent through the transport-provider processes and through the network, regardless
of which processors or nodes they are running on. Even when two processes are running on
the same processor, a message from one to the other always goes to the transport-provider
process first.
For example, given the situation pictured in Figure 5 (page 42), suppose Process 2 sends a
message to Process 4. The following occurs:
1. The message is forwarded by $ZTA01 (the transport-agent process on processor 1 of
Node A, where Process 2 is running) to $ZTC0 (the transport-provider process that supports
the IP address used by Process 2).
2. The message is sent over the network and is received on Node B by $ZTC0 (the
transport-provider process that supports the IP address used by Process 4).
42 Introducing Open System Services