How to Select the Proper PC LAN for Micro-to-Mainframe Connection.
Relatively speaking, the world prior to the PC advance was rather simple. It consisted of more or less homogeneous departmental data communications and processing networks. Workstations were interconnected to processors like IBM 100s, 5520s, DEC Vaxes and Wang IIs. Many of these systems were integrated into corporate-wide data communications networks with the integration achieved by either a computer vendor or a general-purpose data communications manufacturer. For example, computer vendor DEC integrates VAX departmental clusters using DECnet, while turnkey Datacomm systems supplier Codex provides general-purpose networks that are capable of integrating DP devices from a wide variety of computer vendors.
Now, with the rapid proliferation of PCs, there is a corresponding proliferation of local-area network systems designed to integrate PC communications into the installed based of minis and mainframes.
Today there are more than 100 local-area network vendors who either have products available or are planning to introduce products that integrate PCs into existing datacomm networks. The diversity of available LAN systems, including the various topologies, access methods, standards, cabling types and forms of internetworking devices, makes it important for customers to assess and evaluate their current and projected needs before selecting a LAN.
Since the main function of a LAN is to transport data, a major customer consideration will be the capacity for transmission; that is, speed and throughput.
Generally, LANs can be divided into three categories of transmission: those with data speeds over 10 Mb/s; those with speeds of up to 10 Mb/s; and those with transmission speeds under 10 Mb/s.
For large computer communications--mainframe to mainframe installations--LANs with speeds in excess of 10 Mb/s are indicated. One such system, Hyper Channel Network, is offered by Network Systems Corporation. For general-purpose datacomm networks that integrate mainframes, minis and PCs, speeds of up to 10 Mb/s are used. Some examples include Codex's general-purpose datacomm network, as well as LANs offered by Wang and DEC. Standards vary among all three LAN products. Codex's product accommodates diverse computer environments, while Wang and DEC LANs are oriented primarily toward their respective data processing equipment.
The least-expensive LAN system offers transmission speeds of less then 10 Mb/s. Because of its limited throughput, however, it is suitable only for smaller networks, including lower-speed DP devices and PCs.
Whichever LAN appears to be most suitable for your needs today, it is important to consider growth factors (will you need to expand your network geographically?) and the potential requirements for greater throughput (will you be adding more powerful processors to your system?).
Current trends in LAN technology show that during the months ahead LANs will compete on price, performance and innovation. The introduction of VLSI technology into LAN development will contribute to the flexibility of LAN systems while lowering the purchase price. For example, a typical LAN protocol using non-VLSI technology would require about 200 to 300 devices consisting of several printed-circuit boards. One VLSI chip can integrate all this functionality at a much lower cost. Implementation of a protocol in silicon also reduces the learning curve required to design a LAN, therefore reducing time for new product introductions.
In the future, it is likely that LANs will continue to be divided into three segments in terms of transmission speeds. However, high-speed LANs will become even faster, capable of handling up to 20 to 100 Mb/s. This will be necessary to support more-powerful computers that will be introduced. Also, this type of LAN would be used for interconnecting several LAN's into one supernet when a high volume of internet traffic exists (Figure 1, Section A). Fiber-optic technology will replace coaxial cable as a transmission medium in a LAN of this type.
The second LAN segment will provide data transmission speeds up to 10 Mb/s (Figure 1, Section B). LANs of this type will continue to provide access to various DP devices such as PCs, minis and mainframes. Laser printers, file servers, optical storage devices and CAD/CAM workstations will also be interconnected by these LANs. Systems using broadband rather than baseband technology will dominate this segment, because broadband offers higher performance over longer distances and because it can be used to transmit video and voice as well as data.
Developing New High-speed PC LAN
LANs of this type (up to 10 Mb/s) can also serve in the future as "backbones" to newly developed high-speed PC LANs, creating hybrid networks (Figure 1, Section C). Currently, the development for a new high-speed PC LAN that can operate at 10 Mb/s is underway. This LAN, which would operate as a subset of the OSI 802.3 standard called "cheapernet," requires a high degree of VLSI integration in order to make it price/performance competitive. Product introduction is expected in the late 1980s. Connecting this high-speed PC LAN to a general-purpose "backbone" creates a hybrid network that can optimize the use of various diverse DP devices.
The third segment of LANs offers transmission speeds of less than 10 Mb/s (Figure 2). Because of slow transmission speeds, this type of LAN is used solely for PCs and other low-processing-power devices. Most PCs purchased by larger corporations, general-purpose LANs. The lower-speed LANs (under 10 Mb/s) will still be attractive for small networks. However, as the processing power of "business" microcomputers increases, PCs of the future are likely to require the higher throughput of the medium-speed general-purpose LANs.
In this article, we have outlined the three segments of LAN networks. We have also shown how PCs fit into these segments today and in the future. Although small PC LANs will continue to proliferate, the major growth in the future will be in the area of hybrid networks where PC LANs are integrated into medium-speed general-purpose LANs.
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|Date:||Mar 1, 1985|
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