Typically, these are concern with the establishment of
______ the network and with the control of the flow of messages across this
channel. The provision of such facilities is only part of the network
requirements, however, since in many applications the communicating computers
may be of different types. This means that they may use different programming
languages and, more importantly, different forms of ______ interface between
user (application) prograrma, normally referred to, as application processes or
APs, and the underlying communication services may be ______ For example, one
computer may be a small single-user computer, while another may be alarge ______
system. In the earlier days of computer communication, these issues meant that
only closed communities of computers (that is, from the same manufacturer) could
communicate with each other in a meaningful way. IBM’s Systems Network
Architecture (SNA) and DEC’s Digital Network Architecture (DNA) are just
two examples of communication software packages produced by manufacturers to
allow their systems to be int ercormected together. These proprietary packages,
however, of which there am still many inexistence, do not address the problem of
universal interconnect ability, or open systems interconnection. In an attempt
to alleviate this problem, ______, in the late 1970s, formulated a reference
model to provide a common basis (or the coordination of standards developments
and to allow existing and evolving standards acivities to be placed into
perspective with one another.