ABSTRACT
Since the OSI Model was not released before the early 1980s, many manufacturers have implemented their own network architecture which generally does not exactly match the OSI requirements. This is the case with IBM, which designed its own System Network Architecture (SNA), and Digital Equipment Corporation (DEC), which implemented Digital Network Architecture (DNA). Although created a decade before the OSI Model recommendation, these networks have many features that are very close to it. Both networks rely on a layered architecture with seven layers which have slightly different specifications. The philosophies underlying both networks are different. SNA was initially designed to meet the requirements of mainframe-oriented IBM customers, whereas DNA users were more minicomputer-oriented. It is important to keep these ideas in mind when looking at SNA and DNA architectures, since the first architectural design always influences the evolution of a network. Today, however, there is no longer such a distinction between the two networks, since they provide a much broader range of services than they did initially. Both share many networking goals; each offers a common user interface and user transparent network routing and management functions. The following sections describe both architectures, comparing their respective features with those of the OSI Model.
