Expand Configuration and Management Manual (G06.24+)

Planning a Network Design
Expand Configuration and Management Manual—523347-008
3-3
Systems Network Architecture (SNA) Connections
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Low capital cost/high connectivity. X.25 provides a way to connect a large number
of systems through a single line between a NonStop server and an X.25 network.
This feature can lower communications capital costs by reducing the number of
modems and controller ports that must be purchased. For example, a fully
connected network of 4 servers requires 6 links, 12 modems, and 12 hardware
ports. An X.25 network of 4 servers requires only 4 links, 4 modems, and 4
hardware ports.
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Fault-tolerance. Reliability is inherent in the structure of an X.25 network. There
are usually several redundant connections between switching systems in an X.25
network; thus, if one transmission link fails, communications can be rerouted. In
addition, you can use the multi-line path feature to enhance the reliability of X.25
connections. Using this feature, you can configure up to eight parallel lines
between nodes.
The disadvantages of X.25 connections include variable line quality, low speeds, and
long call-setup times. Response time requirements can also rule out the use of X.25
connections because of the amount of time involved in connection-setup and
switching.
Systems Network Architecture (SNA) Connections
Expand-over-SNA connections are provided with the HP SNAX/Advanced Peer
Networking (SNAX/APN) subsystem. The SNAX/APN subsystem can be used to
connect Expand line-handler processes across an SNA network. When SNAX/APN is
used, the Expand line-handler process is configured to communicate with a
SNAX/APN line-handler process that manages the line.
The major benefits of SNA are
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Cost-effectiveness. Expand-over-SNA allows an existing SNA network to be used
to connect NonStop servers. No new lines or equipment need to be set up if
SNAX/APN is already being used to connect the NonStop server to an SNA
network.
•
Fault-tolerance. You can use the Expand multi-line path feature to enhance the
reliability of SNA connections. Using this feature, you can configure up to eight
parallel lines between nodes.
The major disadvantage of SNA connections is the impact of existing SNA traffic on
line capacities. Accurately estimating workloads is essential to predicting cost and
performance of SNA links in an Expand network.
Note. Accurately estimating workloads is essential to predicting cost and performance of X.25
links in Expand networks.