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Digital PBXs Playing Key Role in Today's Info Management, High-Speed Data Needs.

When looking at the different technologies available for local-area networks, the question you are left with is not which technology is best, but which technology best addresses your application needs.

One of these local-distribution systems, the digital PBX, probably already exist in your offices to serve your voice, and perhaps your slow and medium-speed data requirements. I believe you should consider the PBX as a possible solution to high-speed data and information-management requirements.

This article first examines the information-management needs of offices, then reviews the inherent attributes of the digital PBX, and finally explains how PBXs will evolve to address present and future information-management and high-speed data needs.

Until recently, data processing, data communications and voice communications have been served totally separately, but today, with a greater need for information management, these services must be combined to offer users such functionality as electronic mail, multi-media messaging and conferencing, among others. To create these applications, new advanced services have to be designed. These advanced communications services are complex in nature and very expensive to produce.

However, even after designing this functionality, we still have to find an efficient and friendly method of delivering it to the user. Need Single Interface

The information-management systems in our offices today can be described as chaotic, complex and incompatible. Technology improvements have presented the user with an array of new devices, all of which perform a specific office function, but usually in total isolation of each other. Our offices are becoming cluttered with word processors, data terminals and personal computers, each performing a specific function, yet each duplicating part or all of the other's. Few systems offer a user the single interface to all the functionality required.

It's apparent that little further improvements in the efficient management of information in our offices will be achieved until each worker's voice, data, graphics and information-management needs are accessed from a single interface.

Despite the decreasing cost of processing power and memory, it is still not economically viable to design totally self-contained workstations. Reality continues to require that data bases, printers, processors and external communications access be shared. The transmission medium providing access to these shared services is, usually, the local-area network.

The need for multi-media local-area networks is presenting the industry with a dilemma. No single local-area-network technology available today can efficiently and cost effectively support voice, high-speed data and graphics. Therefore, a multi-technology solution is required. If possible, this solution should meet today's requirements, yet be able to migrate to an integrated solution in the future.

First, PBXs provide for the voice requirements of today's offices, using a twisted-pair distribution system. Modern digital PBXs have standardized on a bandwidth of 64 thousand bits per second (kb/s) since encoding techniques have been perfected to give very-good-quality voice transmission at that rate. Coding techniques do exist for lower bandwidth voice transmission down to 9.6 kb/s or below, but they are generally very expensive and lead to significant quality impairment. These modern digital PBXs that have been designed to accomodate voice at 64 kb/s can handle voice or data up to tht speed. Hence they can support most of today's office services, since they almost all have a lower bandwidth requirement. Plenty of Wiring

Digital PBXs have a centralized or star configuration, and use ordinary twisted-pair copper wiring--each office building has plenty of this wiring to each desk.

Because of their centralized configuration, PBXs are easy to administer. Moves and changes today, for example, can often be made by the user or by the PBX attendant. The PBX can also be easily maintained from a central location, and faults can even be diagnosed from remote service centers.

PBXs are circuit switches--that is, they connect two parties physically together for the duration of a conversation and allocate them a standard, fixed amount of bandwidth.

PBXs provide full connectivity in that they allow any station to connect to any other station or to outside lines.

Digital PBXs have been designed to meet the stringent reliability standards of the telephone industry.

Because each terminal device has its own individual connection into the PBX, failures in the terminals, on the wiring or in the interfaces to the terminals within the PBX are isolated from the central hardware--and, therefore, cannot affect the total operation of the system. Duplicated and backup equipment within the PBX permit the system to operate through hardware failures or even in the event of power outages.

Furthermore, additions to the reconfigurations of the system can be accomplished without any interruption in service.

Because they were designed as an element of the international telephone network, they provide interfaces to the full range of intersite communications media including digital transmission facilities. Handle Private Long-Haul

They also support a range of private long-haul network capabilities to decrease costs through features such as least-cost routing and centralized network management, and simplify communications with capabilities such as a uniform network dialing plan.

Advanced digital PBXs accomodate most of today's computers and computer terminals and have brought to local data communications their inherent benefits of full connectivity of terminals and computers to 56,000 b/s, shared access to inter-site communications and the pooling of expensive data transmission devices or modems, provision of advanced calling features and private networking, and the simplification of maintenance and administration through centralization.

The total capacity of today's digital PBX is several hundred megabits, enough to handle many thousands of voice and data devices.

Of particular importance is the degree of adherance to standards by today's PBXs. They support standard telephone instruments and network interfaces, as well as data terminal, computer and network standards.

The major current limitation of the digital PBX is its inability to handle high-bandwidth data communications. Although the 64,000 b/s channel bandwidth of the PBX is adequate for the bulk of today's data communications, the trend toward distributed computing will necessitate bandwidths of 1 Mb/s and greater. A Role for LANs

LANs also have a role to play. LANs are typically based around a single coaxial cable that carries all the communications between different points, or stations. They accommodate up to a few hundred stations, each with a tap on the cable and each with its own complex logic circuit to permit it to transmit and receive information from the shared cable medium.

LANs are packet switches; that is, they transfer bursts of information from many stations, individually packaged and all inter-mixed on the cable. This is often a fine way to transmit data.

LANs also provide connectivity among terminals. Some LANs broadcast the information from each station to all other stations, and only the addressed destination stations will receive it from the cable. A contention problem may arise with some accesss methods where many stations wishing to use the cable try to broadcast at the same time.

Because of the limited total bandwidth of a single cable, most LANs do not have sufficient capacity to carry the high volume of voice traffic in offices. For example, a 10-megabit network would be overloaded by fewer than 100 simultaneous telephone conversations. Further, the protocols used in most LANs can cause lengthy and variable delays that render unacceptable the voice transmission quality. Nevertheless, LANs are needed to handle high-bandwidth data. Match Needs and Options

Having assessed the current and future informtion-management needs of our office worker, and reviewed the important characteristics of the digital PBX and the cable-based local-area network, we can now match those needs against the communications alternatives to obtain an optimal configuration.

It is clear that today's digital PBX can handle all voice communication requirements and most current and near-term data communications, while coaxial-cable local-area networks can handle the need for high bandwidth, bursty data communications required for distributed computing. Optimal Combination

An optimal configuration will require the combination of both the digital PBX and local-area network technologies. The key advantages of this configuration are:

* Large total bandwidth with thousands of connections to support voice and terminal-to-computer communications.

* High instantaneous bandwidth to handle distributed computing.

* Cost-effectiveness for all applications.

* The reliability, administration and maintenance advantages of the centralized configuration.

* Support of the prevalent communications standards.

* The ability to use cost-saving voice features such as hunting and ring-back on data and information-management applications.

In summary, we believe that no one wants more information; they just want better information made more readily available. Northern Telecom believes that there will be a need in the future for a high-capacity connection or a wide information pipeline in the office to every desk. It will be used for our new terminals (and those supplied by other manufacturers) for graphics and for fast fill of data on display screens. It will enable anyone to put a single terminal on a desk for enhanced multi-media communications. Out intention is to advance towards this goal in stages.

You will soon see substantial increases in the bandwidth available on twisted-pair wiring. Since twisted-pair wiring is already available in abundance in every corner of the office, it makes common sense to utilize it when ever possible.

It has already been demonstrated that the telephone wiring in buildings is capable of carrying data at speeds in excess of one million bits per second. This will make the PBX a powerful local-area network capable of handling most information management needs. It will reduce or, in many cases, eliminate the need for the redundant and therefore expensive separate wiring of the coaxial-cable-based local-area networks. The Best of Both

There will continue to be cases where coaxial-based local-area networks will play a role for very-high-speed data transfer. By providing a standard gateway between PBXs and the more widely accepted LANs, the best of both technologies can be achieved; that is, computer terminals on the PBX will have access to to shared resources on the LAN and the LAN will have access to external data networks and resources.
COPYRIGHT 1984 Nelson Publishing
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Copyright 1984 Gale, Cengage Learning. All rights reserved.

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Author:Heather, J.
Publication:Communications News
Date:Jul 1, 1984
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