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PCs that are able to connect to a UNIX system using a WAN approach are generally able to take <br />advantage of the inherent network features rather than having to rely on extensive PC <br />communications software. For example, a PC that can access the Internet (because the PC's LAN is <br />connected to the Internet) can login to UNIX workstations that are at remotes sites (and run programs <br />on the workstations), can transfer files to/from the UNIX workstations, and can potentially display <br />the workstation graphics on the PC (if an X Window System emulation package is installed on the <br />PC). The PC software needed to perform logins and file transfers is generally supplied with the PC <br />network and is also available from public domain sources. The X Window System is the windowing <br />system that is used by most UNIX workstations. The X Window System is public domain and has <br />been ported to PCs by many different companies. X Window System emulation software allows <br />programs running on UNIX workstations to display graphics on PCs as if the PC were a UNIX <br />workstation. This generally gives somewhat subpar performance because PC displays are smaller <br />than workstation displays and PCs generally support fewer colors. However, it does allow PC users <br />to run nearly all of the workstation software while sitting at a PC. <br />Dialup Connections <br />A dialup connection is one where a client host initiates a communication link with a server host <br />when the client needs to access the server. A client is a machine that depends on another machine <br />for a service (e.g., mail, printing). A server is a machine that provides services. For example, an <br />isolated PC may use a modem to link to a bulletin board system that is running on a UNIX <br />workstation. Dialup connections can take advantage of various technology. A dialup connection <br />may be as simple as a modem connection using available PC software or may be an access-sensitive <br />connection that automatically creates a link when a user tries to access a remote site. The costs of <br />different systems vary greatly. <br />One popular Internet dialup service for PC users is SLIP (Serial Line IP). For such a service, SLIP <br />software is provided to the PC user (e.g., use software from an Internet provider or use public <br />domain software). A standard modem is then used to dialup a server machine that provides the links <br />to the Internet. The Internet server machine may be one provided by an Internet vendor (e.g., <br />Colorado SuperNet) or may be a machine that has a modem pool to allow multiple dialups (e.g., <br />Colorado State University). Some Internet vendors have 1-800 numbers to allow portable PCs to <br />dialup while traveling. In general, SLIP connections are billed hourly or monthly. Using an Internet <br />vendor may cost more; however, setting up an internal modem pool can also be expensive in terms of <br />equipment, security, and maintenance. This memorandum does not address the specific costs for <br />setting up such a service. <br />A SLIP connection for a PC allows the PC user to login to a UNIX workstation and transfer files <br />to/from a workstation via the Internet. The user may be able to run graphics programs on the <br />workstation and display results on the PC (using X Window System emulation software on the PC); <br />however, because the modem connection is usually fairly slow compared to direct Internet <br />connections, the performance of such graphics programs may be poor. <br />In general, a SLIP connection or equivalent will give poor results where large data transfers are <br />necessary. In situations where a large transfer is taking place, the PC user may have to wait an <br />?unacceptable? length of time. However, the time spent waiting may be acceptable when compared <br />to the possible alternative of receiving information on a floppy disk delivered by mail. <br />3 <br />A275 06.29.94 1.05-29 Malers <br />