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SNA Terms and Concepts
Basic SNA Concepts
A type 4 or 5 subarea node to which a peripheral node is attached acts as
a boundary node. It performs a boundary function by translating
between the network addresses used by a subarea node and the local
addresses used by a peripheral node.
A simple subarea network includes the following components:
Host
A host is a mainframe computer compatible with the
original IBM System/370. A host is a type 5 node.
Communication controller
A communication controller, also known as a front-end
processor (FEP), is a separate processor attached to the
host. It manages the host's communications with other
computers.
Communications link
A communications link connects the host site with an
end-user site. The users are usually on a separate site
from the host, so the two sites need to be connected by
a communications link.
Terminal controller
At the remote end of the communications link is a
terminal controller, also known as a cluster controller.
It is responsible for controlling the use of the link, and
routes data to the terminals. The most well-known
IBM terminal controllers are the 3174 and 3274.
Terminals
Users run host applications or submit work to the host
from terminals. The best-known IBM terminal is the
3270. A terminal can be connected through a terminal
controller or directly connected to a communication
controller.
Printers
Printers such as the IBM 3287 can also be attached to
the terminal controller. They can receive output from
the host.
As shown in Figure 1-1, "SNA Subarea Network," a diagram of a subarea
network looks like an inverted tree.
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Chapter 1
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