Expand Configuration and Management Manual (H06.21+, J06.10+)

Subsystem Description
Expand Configuration and Management Manual — 529522-013
17 - 56
Sending and Receiving Data
Sending and Receiving Data
After a connection has been established, the local and remote Expand-over-IP line-
handler processes communicate through their associated NonStop TCP/IP or
TCP6SAM processes using the QIO mechanism. You can control how many packets
the Expand-over-IP line-handler process can send to the NonStop TCP/IP process
before waiting for a reply by specifying the TXWINDOW modifier.
To detect loss of connection through the IP network, the Expand-over-IP line-handler
process sends a Probe message to the remote Expand-over-IP line-handler process at
periodic intervals of inactivity.
If the Expand-over-IP line-handler process does not receive a response to its Probe
message, it will consider the line down after exceeding the maximum number of Probe
message retries.
The default inactivity interval (the amount of time the Expand-over-IP line-handler
process will wait before sending a Probe message to the remote Expand-over-IP line-
handler process) is 60 seconds. You can alter the inactivity interval with the Expand
SCF TIMERPROBE attribute.
The default number of Probe messages retries is 3. You can control the number of
times the Expand-over-IP line-handler process will retry Probe messages with the
Expand SCF RETRYPROBE attribute.
Forwarding Expand-over-IP Packets to Other Expand Line-
Handler Processes
Packets received by an Expand-over-IP line-handler process can be forwarded to
another type of Expand line-handler process, either on the same processor or on a
different processor. Packet forwarding is performed via the message system; this
allows servers without Expand-over-IP line-handler processes and pre-D40 systems to
access an IP network.
Figure 17-17 on page 17-57 illustrates the flow of packets between two applications,
one of which is running an Expand-over-IP line-handler process and one of which is
not. In the figure, Expand-over-IP line-handler processes are running on nodes 1 and
2.
Note. The RXWINDOW modifier is meaningless for Expand-over-IP connections but is
provided to maintain commonality among the different line types. Because the Expand-over-IP
line-handler process uses QIO to communicate with the NonStop TCP/IP process and the
NonStop TCP/IPv6 process, the Expand-over-IP line-handler process must read all the
messages on its receive queue at one time; it cannot limit the number of messages read to the
RXWINDOW modifier value because of QIO limitations.