Standards for School Networking
DR. ROBERT D. CARLITZ Professor University of Pittsburgh MYRON LENTZ Director, Office of Computer and Technology Support Pittsburgh Board of Public Education Pittsburgh, Pa. AL MacIlroy President Techera San Diego, Calif. To assure the interoperability, reliability and maintainability of a school district's network, certain standards should be established and followed. This article categorizes these standards and provides a list for designers and implementers. The standards were developed expressly for, and adopted by, the Pittsburgh Public Schools as district policy. The goal of this article is to provide a simple and concise set of standards that school districts can use to facilitate the process of designing and implementing electronic data networks. Such networks are likely to be in increasing demand as new resources and educational applications are developed for the global Internet and as wide area networking increasingly permeates the society at large. In planning the physical connectivity of a school district it is important to develop a broad view of the district's network architecture, including not only the infrastructure of the local area network and Metropolitan Area Network (MAN), but also the set of applications that will initially operate over the network. This ensures that the network will have adequate bandwidth for proposed applications, that these applications will be interoperable, and that sufficient funds will be available for all necessary hardware and software. The Layered Approach Network design can be greatly simplified if one thinks of the network as a set of levels, with each level isolated from those above and below it, and communication to adjacent levels is through a well-defined interface. This architecture allows one to design elements of the network without having to worry about unexpected interactions, incompatibilities or inefficiencies. The idea of a layered architecture has been carried to a formal extreme in the International Standards Organization's (ISO's) definition of seven layers of network structure. Since the ISO definition is more formal than we need in this article, we simplify it by referring to three layers, each of which represents several ISO layers. The three layers are as follows: Physical Layer. This refers to the physical medium through which signals are carried, be it copper wire, fiber optic cable or wireless transmissions. Protocol Layer. This refers to protocols used to encapsulate information and present it to applications running on devices attached to the network. These protocols define a set of rules that enable different entities on the network to communicate with each other. Application Layer. This refers to programs that run on computers attached to the network and provide specific tools or services to users of the network. Physical Layer Currently, computer applications that operate on LANs in the school environment can be handled with inexpensive copper wiring. Present technology allows for operation at speeds of 10 million bits per second, and it is possible to install wiring capable of transmitting data at much higher speeds. A prudent recommendation is to use this type of wiring, known as Category 5 Twisted Pair wire. This choice combines economy of hardware and ease of installation with a reasonable allowance for future expansion. The wiring plant should be a structured one, with a central wiring closet to which classroom or office runs return. Large sites will require multiple closets connected by backbones, which can be constructed from either Category 5 copper or fiber optic cable. Sites of intermediate size may also be served economically with coaxial cable runs in some network segments. Each classroom should have a minimum of three network drops. These drops can accommodate three devices, including classroom telephones as needed. Rooms requiring more devices can use fan-out hardware to accommodate as many devices as might be desired. The choice of three drops is a compromise between convenience and cost and is based upon experiences with this wiring architecture in Pittsburgh and elsewhere. Some redundancy is desirable for ease of expansion, flexibility and added network integrity. The preceding paragraphs refer to premise (building) wiring or to the structure of the local area network within a given school. To connect schools together and provide access to central resources and the Internet, one needs a Metropolitan Area Network (MAN). Neither the precise needs in terms of bandwidth nor the precise solutions in terms of services can be specified at the present time with any great degree of confidence, but graphical applications require a minimal bandwidth on the order of 56 kilobits per second. Services that can provide this bandwidth include: Striped (parallel) modems over mul-tiple voice-grade phone lines 56 kilobit leased lines Frame relay ISDN Fiber optic lines. The layering concept allows one to mix these technologies at different sites in a network so as to obtain the required performance at the most economical cost. Unless one single technology can be obtained at a cost significantly lower than any competing technologies, one should plan to accommodate a mix of technologies at the physical layer of a MAN, with the choice at each site matched to that site's needs and accessibility. Graphical and video applications will eventually require higher bandwidth for many school sites. Here, too, there is a multiplicity of choices: Frame relay (speeds up to 1.5 megabits) SMDS 1.5 megabit leased lines Cable TV If one technology proves much cheaper than the others, it could provide a suitable choice for districtwide adoption. Otherwise one should anticipate a mix of technologies to form the fabric of the metropolitan area network. Protocol Layer This layer includes those protocols that define transport along the physical medium and protocols that present data to applications running on devices attached to the network. Transport over the LAN described in the previous section is conveniently provided via the Ethernet protocol. Atop this protocol sits another protocol that is independent of the physical medium. The choice of protocol at this level is simplified by the fact that the Internet is based upon a common public protocol known as TCP/IP. If students and teachers are to have access to resources on the Internet, then the MAN and LANs in the schools must support TCP/IP. This is the only commonly used protocol that is suitable for application to Wide Area Networks (WANs), and one can anticipate an evolution of popular proprietary protocols for LANs to coincide with TCP/IP in the future. Among the popular proprietary LAN protocols are IPX, used by Novell, and AppleTalk, used by Apple. While both protocols may be of use in specific LAN applications, they should not be extended over wide area connections, except through encapsulation in TCP/IP. To isolate applications from the raw TCP/IP protocol, vendors have developed standards through which their applications receive data from the network. On the Macintosh platform the standard interface is provided through MacTCP, while on Windows machines the standard interface is known as Windows Sockets (WINSOCK). By enforcing these standards for each of these platforms, one can insure the interoperability of all network applications running on any given machine. Application Layer Standards issues at this layer have to do with how applications handle data. We presume the existence of a networked environment, with all computers and peripheral devices connected to it. Standard applications are available via file servers and maintenance of commonly used software can be provided remotely. Local software can be added to individual classroom machines or installed on school-based servers. Virus-checking utilities protect individual machines and the file structures for these machines can be rebuilt from the servers if their integrity is severely compromised. Applications that support native-mode standard file formats can exchange data and interoperate across the networked environment. This is an evolving area, as new applications are continually being developed, but one can discuss a few general issues and several specific issues that presently apply. Among the general issues is that of how multimedia is handled. This question applies to e-mail, news and various network applications. The most widely employed standard is known as MIME (Multipurpose Internet Mail Extensions). It is reasonable to demand that mailers, news readers and network applications that support multimedia should all adhere to this standard. The MIME standard is extensible, since it specifies external programs or "viewers" for any given multimedia file type. This enables it to accommodate a variety of text types, graphics formats, video and sound, as well as such specialized elements as databases and spreadsheets. Specific issues relate to the user interface and file formats. For the first, a standard user interface can be specified in terms of utilizing a graphical display with a keyboard and a pointing device such as a mouse or trackball. Such interfaces are provided with all current commercial devices. Specialized interfaces, such as voice synthesizers and mechanical assists, should be provided for users with special needs. For the second, interoperability demands either that applications use a common file format or that they have file conversion capabilities. The lowest common denominator for file exchange is that of ASCII text and all programs should support this format. One level up is a standard known as Rich Text Format (RTF), which allows for the specification of font information and attributes. This, too, should be supported wherever possible. At a basic level, user frustration can be reduced if a single product is deployed districtwide for each of the most common computing tools: word processing, databases and spreadsheets. Not all available software meets all of our standards at the present time. In order to provide students with access to products found in the typical commercial workplace it is therefore necessary to make some compromises in strict adherence to these standards. A convenient mechanism is to develop a districtwide list of currently supported products. This list should further indicate the extent to which the products meet the standards as well as the reasons for relaxing standards in certain cases. Attached Hardware Specific devices to be attached to the school network also have minimum "standards." Personal computers, for instance, should have a monitor/video card combo capable of running a windowed environment, an Ethernet interface and the processing power to run commonly needed applications. These requirements can be met with any of a number of models of Macintoshes, IBMs or IBM-compatibles running Microsoft Windows, OS/2, etc. Prudent recommendations for a minimal configuration of such machines are as follows: 8MB internal memory (RAM) 200MB hard disk 800 x 600 pixel display with 256 colors 14" display screen Intel i486, Motorola 68040 or PowerPC processor In addition, there are several other components required to make the network and its attached information resources function. These can be listed as follows: Servers. These machines provide file service, print service, information resources and mail. A true multi-tasking operating system is required to support this range of services. Typical devices for this task are RISC-based workstations running the UNIX operating system. Other processor platforms may be adequate for smaller sites; other operating systems (notably Windows NT) may prove suitable for this purpose as their installed software base increases in size. Routers. These devices provide connectivity to a metropolitan area network. The choice of TCP/IP for MAN connectivity requires that the routers support this protocol. Multi-protocol support, including IPX and AppleTalk, can be a useful option but increases the maintenance required. Peripherals. This category includes printers, scanners, CD-ROM drives, tape drives and other devices. Where standards exist in terms of file formats, these should be respected in most school district purchases. Relevant standards in this area include PostScript (a page description language for printers), Kodak's Photo CD format (for CD-ROM drives) and TWAIN (for joining together scans made on a flatbed graphic scanner).
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Networkable devices are preferred for reasons of economy and flexibility. A high-volume, networked laser printer can, for example, serve a classroom more conveniently than multiple impact printers attached to individual computers. As with application software, this is an area in considerable flux, and standards should be reviewed on a regular basis. Robert Carlitz, a professor of physics at the University of Pittsburgh, is moderator of the KIDSPHERE mailing list and project director for the school networking testbed called Common Knowledge: Pittsburgh. E-mail:
[email protected] Myron Lentz has been director of Computer and Technology Support for the Pittsburgh Public Schools since 1975, providing central district support for technology planning including the design and maintenance of wide and local area networks. E-mail:
[email protected] Al MacIlroy is the president and CEO of Techera in San Diego, Calif. The firm is developing an instructional management software system for teachers and administrators, and d'es consulting nationally to aid schools or districts with their instructional technology planning MacIlroy is a former vice president of Jostens Learning (Education Systems Corp.). E-mail:
[email protected].