components that make up an SNA design, what each component does, various methods and
benefits of each design, and also how Cisco routers fit into the design.
uses polling and is connection-oriented, this technology has managed to outlast a host of others
and is still considered a worthwhile investment even though it was introduced in 1974. This
chapter discusses some of the fundamental roles of SNA hardware and software and where
Cisco routers fit into the SNA picture. SNA is certainly not a new technology, but it is still
widely used for a variety of purposes and will probably continue to be for some time. Design
professionals need to know which considerations to watch out for.
connected to multiple terminals. The mainframe computer polled the terminals, asking each one
if it was ready to send data. This is how polling technology began.
terminals that connect to a central mainframe computer. It is the mainframe's job to poll the
terminals in the store and then accept transactions and do all the processing. Another example would
be a racetrack, which might have anywhere from 200 to 600 terminals for people to place their bets.
After you place your bet, the machine notifies the mainframe that it has a transaction to process. The
mainframe processes the information and signals the machine to print the ticket for you.
from that of the OSI model. It might make sense to first compare the SNA model to the OSI
model and discuss some of the general differences between TCP/IP and SNA before going on
with the rest of the chapter. The SNA model is described in Table 12-2. It is functionally
equivalent to the OSI model.