OSI for Libraries: Standards to Services (1992)

5. TELECOMMUNICATION OPTIONS

• the OSI protocol suite based on the OSI Reference Model
  
• the TCP/IP protocol suite which is the Transmission Control Protocol/Internet Protocol and the most widely used set of standardized, vendor-independent protocols
  
• vendor-specific suites such as Digital Equipment Corporation's DECNET and IBM's System Network Architecture (SNA).

All of these suites, plus those proprietary to local telecommunication service providers, can support connectivity between computer systems. However, the ones most likely to be considered by libraries are either OSI or TCP/IP based.

5.1 OSI Telecommunications

Messages pertaining to the SR standard can be transmitted via a direct connection between the communicating computers using the OSI protocol specification for Association Control Service Element (ACSE), and standards at the presentation and session layers and at the remaining layers that support transport.

The availability of OSI-based telecommunication networks is not as prevalent as one may expect, given the degree to which OSI has been predicted as the basis for networking. The protocol suite that has attained a stronger foothold is TCP/IP (Rose, 1989).

5.2 TCP/IP Telecommunications

As more networks were connected using the TCP/IP protocols, the interconnected group of networks came to be known as the Internet. The Internet has grown almost exponentially in the last two years, and now spans most of North America and has reached well into Europe, Asia, and Australia. Libraries, particularly those linked to universities, are beginning to use the Internet to support library operations and it is now possible to access many automated library catalogs via the Internet. Further discussion of these initiatives is provided in Report #1 of the UDT series on Data Communication Technologies and Standards for Libraries entitled Research Networks and Libraries, Applications and Issues for a Global Information Network (Cleveland, 1991a).

The increase in the use of research networks has been coupled with debate about which protocol suite is the most appropriate to meet the networking needs of libraries. Therefore, it is useful to explore the differences and the similarities between the two protocol suites. Each suite attempts to provide the end user with a standardized method of accessing an underlying physical network, but they differ in how they provide this access. Rather than consider them as opposing options, is it possible to view them as co-existing to improve the way libraries communicate with users and other libraries.

5.3 Comparing OSI and TCP/IP

Figure 2 - Comparison of the OSI and TCP/IP layered architecture (46 K)

At the transport layer, however the models begin to diverge. Unlike the OSI model, TCP/IP does not define a session or presentation layer. The TCP/IP application protocols interact directly with the TCP services.

The TCP suite includes four principal application protocols: simple mail transfer (SMTP), file transfer (FTP), remote login (TELNET) and network management (SNMP). In general, these applications are not as functionally rich as their OSI counterparts, namely Message Handling Systems (MOTIS or X.400), File Transfer and Access Management (FTAM) and Virtual Terminal (VT). The TCP/IP applications are also correspondingly less complex and therefore easier to implement and test.

The OSI applications were developed within the international standards arena, and a great deal of effort ensured that these applications provide the full range of services required in an international networking environment. They therefore include support for complex data types and multiple character sets, and they are highly extensible. The TCP applications were developed in a more focussed environment where interconnectivity needs were addressed in the simplest and most efficient way possible. They therefore generally support simpler data types and a more restricted range of character sets.

The TCP/IP protocol suite is now very widely used, not only in the academic and scientific community, but increasingly in commercial and industrial applications (Lynch, 1990). It is possible to purchase off-the-shelf TCP/IP software that is reliable and will operate on a variety of hardware platforms. There is also a large installed base of TCP/IP-based networks that one can connect to and the protocols have been well tested in real implementations.

In contrast, OSI products are just beginning to emerge in commercial products and remain to be tested extensively in operational environments. There is general agreement that OSI application standards are architecturally superior in that they provide a flexible interface for foreseeable network communication needs. There is, however, concern that the computing overhead needed to implement the expanded services offered by OSI may slow down network operations considerably and/or cost too much.