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Local Area Networks for Radiology Local Area Networks for Radiology Samuel J. Dwyer, III, Nicholas J. Mankovich, Glendon G. Cox, and Roger A. Bauman This article is a tutorial on local area networks (LAN) area were connected to a concentrator which was for radiology applications. LANs are being imple­ connected by a single communication link to the mented in radiology departments for the manage­ central computer. This reduced the cost of data ment of text and images. replacing the inflexible point-to-point wiring between two devices (com­ communication links by replacing a number of puter-to-terminal). These networks enable the shar­ them with a single link. Second, the computer ing of computers and computer devices. reduce was relieved of all communication processing equipment costs. and provide improved reliability. tasks by special processors called front ends. Any LAN must include items from the following four In the early 1970s, large area data networks categories: transmission medium. topology. data transmission mode. and access protocol. Media for became available for connecting multiple com­ local area networks are twisted pair. coaxial. and puter systems and peripheral devices. These net­ optical fiber cables. The topology of these networks works became known as wide area networks. The include the star. ring. bus. tree. and circuit-switch­ cost of communication links in these wide area ing. Data transmission modes are either analog sig­ networks remains a significant percentage of the nals or digital signals. Access protocol methods include the broadcast bus system and the ring sys­ total operating cost. tem. A performance measurement for a LAN is the In the 1980s, solid state technology advances throughput rate as a function of the number of active have provided the powerful microcomputer sys­ computer nodes. Standards for LANs help to ensure tems and inexpensive data communication that products purchased from multiple manufactur­ devices of today.l" These developments have ers will operate successfully. @) 1988 by W.B. Saunders Company. permitted movement away from large time-shar­ ing computers to distributed processing and KEY WORDS: Local area network (LAN). transmis­ resource sharing via inexpensive data networks. sion medium. topology. data transmission mode. By encoding data into small packets, it can be acess protocols. throughput. and standards. transmitted over a network and reassembled at the receiving site. In the middle 1980s, single N THE EARLY 1950s, central computers owner, small area data networks were developed. I were connected directly (point-to-point) to These small area data networks are called local terminals, printers, and other computer periph­ area networks (LANs).s-s eral devices. The number of peripheral devices Using either a wide area network (many and communication links increased significantly miles) or a LAN (several miles), one is able to in the early 1960s with the introduction of time­ access any computer or computer device on the sharing computers. Time-sharing allowed a network (assuming necessary security approv­ larger number of users at remote sites to satisfy als). Personal computers can act as a computer their computer needs without having to travel to or as a terminal over a network. The networks are the computer facility. As these remote devices combinations of hardware and software dedi­ increased in number, the cost of point-to-point cated to markedly more flexible access to and links became large. from sharing of resources."!' The possibility of Two significant developments reduced the cost electronic mail over the entire network is an of these point-to-point communication links. added benefit. First, a number of remote peripherals in a small This tutorial is intended to provide an intro­ duction to the basics of LANs. These LANs are From the Department of Diagnostic Radiology. Univer­ already in place in many small and large radiol­ sity ofKansas Medical Center. Kansas City; and the Depart­ ogy departments. They are used to link two or ment ofRadiological Sciences. UCLA School of Medicine, more personal computers to each other and to Los Angeles and the Department ofRadiology. computer peripheral devices in office automation Address reprint requests to Samuel J. Dwyer, Ill, PhD, and billing systems. The terminals and other Department of Diagnostic Radiology, The University of Kansas Medical Center, Kansas City, KS 66103. devices on radiology and hospital information © 1988 by WB. Saunders Company. systems are often connected via a LAN. LANs 0897-1889/88/0101-0004$03.00/0 also move images between devices in picture 28 Journal of Digital Imaging, Vol 1, No 1 (November), 1988: pp 28-38 LOCAL AREA NETWORKS FOR RADIOLOGY 29 archiving and communication systems. No other device. Protocols are the sets of rules and attempt will be made to provide details of those conventions governing communication on a net­ applications other than a few diagrams. work. These protocols minimize the collisions The focus ofthis presentation is to identify and that may occur when two or more users attempt introduce the components of a LAN and how to transfer data simultaneously. they work together. These LAN components are Historically, digital communication technol­ the transmission medium, the topology, the data ogy for a LAN began with the packet-switching 12 13 transmission mode, the access protocol, and the ALOHA radio network in HawaiL • The network nodes (computers and other devices). ALOHA network was established to provide Because there are many possible ways to com­ access for a large number of terminals connected bine components from these categories, it is to a central computing facility. Packets of data virtually impossible to simply name a LAN were broadcast on a radio channel and received without many qualifiers (exception: a commer­ by the central computer installation. Ethernet cial product name). Talking about a fiberoptic was subsequently developed replacing the radio LAN gives information only about the transmis­ channel by coaxial cable.":" Many subsequent sion medium, a very incomplete description. LAN designs have provided significant improve­ Teasing apart the various component parts of ments. Increased demand for LANs includes LANs will help to remove some of the mystery widespread applications for interconnecting that the many terms tend to create. large computers, workstations, and business The transmission medium of a LAN is the equipment in an office in the same building, physical medium used for the interconnection. microcomputers and digital devices in the same The electrical signaling rate on a LAN over building or between buildings, and image man­ various transmission media ranges from I to 50 agement networks. megabits per second (Mbps). The actual Radiology departments are already using per­ throughput of data transferred between two con­ sonal computers, file servers, printers, and LANs nected devices varies from 50 kilobits per second for a number of office automation functions. (Kbps) to 6 Mbps. This disparity between signal­ Figure 1 illustrates a LAN in a professional fee ing rates and throughput data rates is due to the patient-billing system which manages patient overhead necessary to operate a LAN. The topol­ billing, insurance claims, on-line history, and ogy of a LAN is the connection arrangement of transaction files. Furthermore, it acquires the computers and computer devices. The access patients' demographic data from the Hospital control method is the user communication proto­ Information Management System, transmits col for transferring data on the LAN. Every third-party payment requests, and generates connected device can communicate with every revenue reports. The computer nodes are micro- Electronic Claims Hospital 14----. SMS System Fig 1. A LAN for a profes­ sional fee patient billing sys­ tem. 30 DWYER ET Al Hospi tal Nuclear Film IMS Med. Room 286 Micro Roentgenology '------------1AIi~be MRI Sono CT/Specials Portables Network Controller Roentgenology Professional Fig 2. A LAN for a radiol­ Fee ogy information management Billing System system. computer workstation systems, a file server nodes provide for the on-line, high access rate microcomputer, a microcomputer for running storage and retrieval of the digital data. Long­ the management programs, and a laser printer term archiving nodes provide medium access rate (15 pages per minute) for printing patient bills, storage and retrieval of digital images. Interfaces claim forms, and reports. The LAN is a 2.5 to the department and hospital information sys­ Mbps token-passing network using a distributed tems are required. star topology. This professional fee billing system processes 450 patients per day, or an average of TRANSMISSION MEDIUM FOR A LAN 625 examinations per day. Commonly used transmission media for LANs Figure 2 illustrates a LAN for a radiology are twisted pair, coaxial, and optical fiber information management system that can pro­ cables.":" A twisted pair consists of two insu­ vide information about patient scheduling, flash lated wires arranged in a regular spiral pattern. card generation, film file room cards, manage­ The wires are copper, which provides electrical ment reports, and can track the patient through­ conductivity, or steel coated with copper. Twist­ out the department. The computer nodes are ing of the wire pairs minimizes electromagnetic microcomputer workstations, a microcomputer interference. Twisted pairs are widely used for file server, and printers. The LAN is a 2.5 Mbps analog telephone
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