Library Technology Guides

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Volume 4 Number 09 (September 1984)

Local area networks for data communications

Increasingly, libraries affiliated with academic institutions and major corporations are becoming involved in discussions on the use of local area networks to meet campus-wide data communications needs. Some 20 universities and several hundred corporations have installed, or are in the process of installing, LAN systems. The initial investments range from $500,000 to $7 million. Among academic users are Brown, Carnegie-Mellon, Lehigh, Rochester Institute, Pepperdine, and Stanford.

A local area network (LAN) is a facility which provides data and voice and! or video communication within a single building or a close cluster of buildings, although in some rare cases a LAN can be utilized over distances as great as 20 miles. A LAN uses "local" communications facilities rather than those provided by a common carrier or public communications service. Thus, LANs do not utilize public telephone systems, public access long distance networks, or other public communication channels. This does not mean that they cannot connect to public communications services-some do so using "gateways" but rather that these boundaries define the LAN.

Typically the computing resources of an academic institution include a number of different types of mainframes, minicomputers and microcomputers from a variety of vendors. They are rarely single vendor environments. The ability of the more sophisticated LANs to support linkages among machines in a multivendor environment is a major advantage. Multivendor LAN interfaces typically offer "bit carrier' capabilities as a minimum, and at a maximum, provide true file interpretation and linkage between dissimilar devices.

LAN linkage in a multivendor situation may also offer other advantages, greatly reducing modem and data line expenses, increased sharing of expensive resources, reduced need for communication controllers and optimized utilization of ports on a host processor.

LANs have many different applications. In an office situation, a LAN can readily replace much of today's paper flow with electronic documents. In this situation the LAN can transmit budget material generated by personal computer-based spreadsheets among the personal computers themselves and on to a host computer. Computer resources can be shared campus-wide, with each terminal or micro on a campus being able to access every computer. High-speed printers, plotters, CAD (computer aided design) units, and other special devices can be shared among many users. Data bases can be made available throughout a campus.

A review of the significant design concepts of LANs may be helpful in understanding their use. The important aspects are:

• Circuitry-the physical media need
• Access Methods-the approach used to handle access to the LAN by the devices connected to it
• Topology-the physical design of the LAN
• Bandwidth-the measure of the throughput capacity of the LAN

Circuitry. Although a variety of LAN circuitry is possible, the most common circuit types are coaxial cable and twisted pair telephone-type wires. In the future, fiber optic cable will be more common. LANs usually accommodate the most common established forms of data transmission. A LAN typically transmits data in small chunks, or packets, and adds transmission routing, addressing, and sequencing data to each packet. "Packet switching" transmission is used because it provides better utilization of the network circuits than techniques which transmit an entire message in a continuous string (message switching).

Access methods. To transmit data effectively, a LAN must prevent data collisions which could occur when two or more devices want to access and send information on a single channel at the same time, Strategies used to avoid collisions include Carrier Sense Multiple Access / Collision Detection (CSMA/CD) and token passing. Under the first method, a device trying to send a message first checks whether the line is "busy." If not, it proceeds to send its packet, or packets. If the packets are received correctly, communication continues normally. When two devices attempt to send simultaneously, a collision is detected and each device waits its own randomly determined time period before retransmitting. Token- passing access methods permit a device to transmit only when it possess a logic "token." The token is passed between devices in the network in a predetermined sequence.

Both methods are intended to allow interconnected devices to communicate efficiently without requiring a master network controller of the type usually employed in computer terminal networks. Where a LAN network controller is present, it typically directs the communication flow on the overall network level rather than at the device level. The connected devices are responsible for their own data stream control and communication session management. In this regard, LAN communication requires a minimum level of local intelligence at the connected device or the cable interface unit.

Topology. The topology of a LAN usually follows one of three configurations:

• Star
• Data Bus, or
• Ring.

In a star configuration, all devices are connected to a central control point using a single line for each connection. Many star LANs are PBX-based, rather than being independent and using their own coaxial cabling. They are, therefore, operationally dependent upon the reliability and loading of the central PBX controller. Although recent advances in transmission technology have increased the throughput of PBX-based lines, they often have a relatively slow transmission capacity--56 kilobits/ second-for each twisted pair wire.

In a data bus structure, all connected devices typically tap into a single line or bus. The data bus cable is usually Open-ended. Information packets flow outward in both directions from each point of connection. Data bus LANs are usually based on coaxial cable and may utilize dual parallel cable--one cable for traffic flowing in each direction.

A ring network connects devices in a fashion similar to a data bus LAN, but connects the ends together to form a continuous loop. Because of this circular shape, information packets can be routed in one direction around the system and all data will be received by all connected devices. Many such LANs use token passing and place a token at the start of a packet to indicate whether it is already full or may be loaded with more data.

Bandwidth. The terms "baseband" and "broadband" describe the transmission capacity of the LAN circuit and thus the total net throughput provided to the user. Under a baseband approach, the entire capacity of the LAN or the data channel is utilized by one user at a given moment. While the speed of transmission is quite fast, typically 2 to 15 megabits/second, the entire capacity of the system is dedicated to one user at a given moment.

With a broadband approach, the capacity of the system is divided into segments, or channels. Each channel may be assigned to a different use. In this manner, hundreds of users may concurrently use the LAN capacity for widely different applications. Because the transmission capacity is divided into multiple segments, each carrying a major communication load, the total capacity of the broadband LAN is far greater than that of a baseband LAN.

A local area network may use several different design approaches. For example, a broadband LAN may be installed as a spine or backbone to provide high capacity linkage through a facility. Baseband LANs may then be attached to this backbone to handle connections, especially those with low volume users.

A major factor in deciding on the design of a LAN is the applications which are to be supported. The throughput capacity requirements in bits per second for various types of LAN applications are:

Telex	55
Data from a voice grade phone line	2,400-4,800
Telephone speech	64,000
High-fidelity stereo music	1,000,000
Compressed digital video	,000,000
Broadcast color video	92,000,000

The total distance to be covered can be important, particularly if a baseband LAN is planned. In some cases, a baseband LAN requires repeaters every 500 yards to boost signal strength. With broadband LANs, distance is less of a limiting factor, but they do require signal amplifiers to overcome long-distance signal loss.

In the case of a relatively complex LAN installation, planning and design typically account for one-third of the budget, hardware one-third, and installation one-third. In coming years, LAN hardware components, including those borrowed from the CATV industry, should generally drop in per-unit price. The planning/design and installation labor cost will probably continue to rise, however.

LAN vendors typically fit into one of three categories:

• Office equipment suppliers who developed local area network products to tie together their product family, or so they could coexist in a multi-vendor environment.
• Advanced telephone system and/or PBX manufacturers who have become involved in data switches and LANs as extensions of their business.
• Independent communications suppliers and CATV equipment manufacturers with LAN products as their primary product offering.

Suppliers generally approach the LAN market in quite different ways which reflect their origins.

Office data processing and word processing systems suppliers generally developed LAN products which "protected" their installed base of products. At the same time, they continued to promote or extend existing communications approaches. The LAN products from such firms tend to be well developed and reliable, but not designed to offer "breakthrough" capabilities or sophisticated network services such as automatic code conversion. They generally comply with existing communications standards and are rapidly moving toward supporting multivendor LAN installations.

Suppliers from a PBX background usually provide LAN products derived from data switch methodologies. These LANs tend to promote ease of use and low cost workstations, sometimes at the expense of functionality. In many cases, their approach is to attempt to displace more costly personal computers with less functional devices that provide digital voice linkage and host computer data access. The emphasis is toward large numbers of low-cost "dumb" workstations interconnect through intelligent PBXs.

The third group of LAN suppliers, firms mostly in the LAN and CATV component business, are often smaller organizations. These companies have tended to accelerate the development of LAN products up to the limits of their resources. The LAN products from these firms are not always the lowest cost alternative, but are quite flexible and may be the only real choice for unusual requirements.

In terms of likely future developments, at least three major areas of significance stand out:

• Physical circuitry
• Network intelligence, and
• Standards.

LAN physical circuitry will include increasing use of fiber optics. The trend toward increasingly complex personal computer color graphics and multiple windowing will increase bit loads and therefore encourage the use of fiber optics to handle the traffic.

LANs will probably provide more "value added" services in regard to network intelligence with the LAN of the future moving beyond the role of being a high volume bit carrier to providing more automatic data conversion services and interpretation during transmission. LAN network management services will offer increased security provisions and possibly some form of encryption. Additionally, a dynamic storage management capability is needed. Future LANs must be able to automatically move data files to their highest volume point of usage. The increasing size of local data disk storagemagnetic, optical, or other --should make such dynamic LAN data management capabilities realistic and cost-effective.

LANs will most likely adapt to new standards--either official or de facto--as these emerge. They will accommodate related new product trends such as personal computer graphics and other options.

Loading separate bibliographic files on an automated system

In the July 1984 issue of LSN we highlighted the importance of ownership of records as a consideration in retrospective conversion planning. In this issue we examine some of the factors to be taken into account when a library or group of libraries wishes to combine separately developed files of machine-readable records into a single data base on an automated library system. This need arises when a library has bibliographic records from different sources such as a book jobber, a bibliographic utility and a retrospective conversion vendor, or when a group of libraries wish to mount their separate machine-readable files on a shared automated library system with a single bibliographic master file. The following discussion focuses on bibliographic records formatted according to the accepted national standard-the MARC format.

The vendor of an automated library system will normally undertake the merging of separate files and the deletion of duplicate bibliographic records as a part of system implementation. It is also common practice for system vendors to provide the software required to translate standard records from sources such as OCLC and MARC/REMARC into the internal format used by their systems. Another process, often performed at this time, is to separate the item-specific or individual copy information from the bibliographic records and use it in the creation of separate copy records.

To verify that this generalization was correct, the editors contacted three representative turnkey system vendors. Their responses are described in the following paragraphs.

OCLC, the vendor of LS/2000, confirmed that the combination of separate files, the translation of files from "regular" sources such as MARC/REMARC into the format used by LS/2000, the elimination of duplicate bibliographic records, the retention of local information recorded in the copies of a record not selected for retention on the master file, and the generation of item records are processes handled by the system. Except in the case where special programming is required to handle nonstandard record formats, such processing incurs no charges. However, these are time consuming processes-for example, the generation of item records and the associated creation of indices and authority files can require up to a minute of computer time per record. In very large files, this could translate into a "time" cost since the system is not available for regular use until the processing has been completed.

CLSI confirmed that system software has been developed to match and merge records from separate sources into a single combined data base. Libraries would need to purchase the required software, as part of the general system software purchase, and would also have to buy or rent a tape drive to load the records. The software for this operation is parameterized, allowing a library or group to establish its own criteria for the circumstances under which bibliographic records ate considered to be identical. This method of loading and matching records from different sources incurs no per record charges.

However, CLSI customer libraries can expect to incur per record costs in the creation of copy-specific records. Unless the item data has been entered into the 049 fields of the bibliographic records as required by the CLSI format, the company has found it necessary to undertake custom programming for each different customer. The tapes are then processed through the specially written programs before they are mounted onto the local system and merged. CLSI personnel estimate the charge for this programming at between $.05 and $.10 per item record created. The system creates the appropriate item records at the same time that the processed tapes are loaded and merged into a single bibliographic file. None of the local data input during the conversion are lost when duplicate bibliographic records are deleted -- this information is transferred into the appropriate item record.

The current processing procedures of DataPhase, the third vendor queried, may present problems. The potential problems occur not in merging the files or in eliminating duplicate bibliographic records, but hi retaining the individual copy information-the local data- included in the bibliographic records. At present, this data is not retained for any record other than the one selected as the master record for the bibliographic file. The copy specific or individual copy information is purged along with the duplicate bibliographic records.

DataPhase systems include the software for tape loading and matching. A tape drive is a mandatory part of the system configuration so it would not be necessary to lease one for the loading and merging operation. Records in the MARC format can be loaded without difficulty. However, unless local/copy information has been recorded in the 949 field in accordance with the DataPhase format, this information cannot be processed and is dropped from the record. One way to overcome this is to have the tapes preprocessed by a tape processing service, transferring the local or copy specific information into the required field and into the DataPhase format. However, even this does not overcome the problem of losing item specific data when there is more than one occurrence of a bibliographic record.

In the method used to retain the selected record, all of the record is retained (including the item data provided that it is recorded in the 949 field in the Data Phase format). However, this is not supplemented by any information from the duplicate records. Therefore, the item specific information included in duplicate records is lost in the match/merge process and must be rekeyed.

Data Phase offers libraries several options for comparing multiple records to identify duplicates. The choices are: the 001 field; the 035 and 010 fields; or all three fields. In the implementation of some of these options, the system software can be instructed to select the record to be retained as the master bibliographic record on the basis of the encoding level of the record-the "highest quality" record being the one selected for retention. Libraries can also choose whether such selection should be implemented automatically or whether the records should be referred to a file for later human review.

The procedures and costs for file merging on the three vendor systems described above also apply to a library seeking to add its records to the data base of an existing automated system. However, additional charges may be incurred in this situation. The library which owns the system may seek to impose a charge to perform the required processing. This might be justified due to the processing time required to undertake the merger, and the fact that such processing might restrict normal system use or performance.

Specific negotiations on this point should be conducted prior to finalizing arrangements for a library to join an existing system. For comparative purposes, the costs quoted by the system operator can be compared to the charges that would be levied by one of the many processing services which specialize in library-related tape processing. SOLINET, for instance, has the ability to "break-out" copy information from bibliographic records and create item records. To date, this capability has been demonstrated for records to be mounted on LS/2000, CLSI, and DataPhase systems. AMIGOS also provides similar services. The same capability is now being developed for Geac systems. The vendor of the system on which the file is to be mounted may also be able to suggest suitable sources for such support.

High-density television in offing

For decades scientists have been conducting research to determine the ideal television image. They have concluded that a television system with 1,500 scanning lines would improve picture resolution more than three-fold over the standard 25-inch monitor/ receiver television picture. High definition television (HDTV) is a key development which will affect television and movie viewing in the future. In contrast to current television standards of 525 scanning lines, HDTV utilizes 1,000, 1,550, and even 2,000 scanning lines. The doubling of resolution creates an image five to ten times as detailed as that available on current television receivers. HDTV also provides the potential to increase screen size by as much as 25 percent without additional distortion.

The standard HDTV produces a television picture which provides the same picture quality as 35mm film and shows the average 8 by 11 inch typed page with a clarity that is legible. Unfortunately, the image produced by the 1,000 scan lines, though legible, may be uncomfortable to read for extended periods. Philips, a Dutch electronic conglomerate, is therefore engaged in projects involving the development of screens ranging up to 2,000 scan lines per frame which would display text with the clarity of a printed page.

The basic technology for HDTV already exists; however, cost and regulation are major obstacles to its practical application. Before HDTV can be utilized by the public, the Federal Communications Commission (FCC) would have to allocate new channel space. The broadcast bandwidth needed to accommodate the entire signal would be 30 MHz, the equivalent of five times the present NTSC (National Television Standards Committee) standard.

The wider bandwidth of HDTV would require replacing the present VHF and UHF technologies with satellite distribution or digital transmission using optical fiber or coaxial cable. Images could be sent from satellite to cable companies for distribution or directly to an individual consumer s satellite dish. The signals would have the quality of images of 70mm film or theatre film projection.

Several technical barriers must still be overcome before HDTV becomes reality. For example, broadcasters must invest in new cameras and other studio equipment. In addition, refinements of a high resolution tube, a television projection display system and video recorders are needed. Perhaps the greatest obstacle to the broad application of HDTV is that viewers would also have to replace their television sets and video cassette recording machines.

High-density television could play a dynamic role in the future. Movies might no longer be shot in 35mm or 16mm but with HDTV cameras in video. HDTV would allow editing, production, release, and display- all on videotape. Detail, color, and sound would be better than that achieved with the 16mm or 35mm film. The high-resolution pictures available for video transmission would transform the use of images in such fields as art, botany, zoology, medicine, geology, and physics. In addition, the ability of HDTV to transmit legible text would have an impact on videotext systems.

Videotape applications are likely to become available before HDTV becomes the norm in the broadcasting industry because it will not require FCC action. The first direct broadcast satellite may not be launched until 1986. CBS is presently studying the possibility of achieving a higher quality image by transmitting HDTV through two channels simultaneously. Consumers could achieve a high definition picture by tuning into both channels at once or by purchasing an upgraded television set. This would ease the entry into the new technology.

There will also be a gradual change-over to digital television receivers, which use semiconductor chips to convert broadcast signals into digital code.

Digital TV also provides better picture quality. Sony, Panasonic and Quasar are currently developing this capability and expect its widespread adoption to coincide with the emergence of HDTV.

Ameritech markets data communications

Ameritech, the Bell Operating Company which serves the Midwest, has launched an aggressive entry into data communication. While prohibited from entering the data processing field, the company is unrestricted with regard to data communication. It may even market outside the five-state area in which it provides regular telephone service.

In the next fiscal year, the company will invest $.5 billion of its $1.7 billion capital budget to replace analog switches with digital equipment and to augment present transmission facilities with high capacity fiber optic cables. The company's present transmission facilities can reach 86 percent of the customer base with 56,000 bit per second service, but the switches have limited transmission to 1,200 bits per second-the speed at which most terminals to automated library systems now operate.

Metropolitan area networks using packet switching technologies are planned for the second half of the 1980s.

[Contact: Ameritech, 225 W. Randolph, Chicago, IL 60606. (312) 750-5000.]

Caring for, and housing, a computer

A subscriber recently recommended the following volume as a basic guide to the care and housing of computers. DON'T (or Row to Care for Your Computer) by Rodnay Zaks is published by SYBEX, Inc., of 2344 Sixth Street, Berkeley, CA 94710. The book contains specific chapters on file structure, computer operation, terminals, printers, hard disks, tape drives, floppy disks, the physical environment, documentation, security, and software.

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