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<UL>
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<A HREF="#E68E98" >Understanding Network Topology and Operations</A>
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<A HREF="#E69E238" >The Scope of PC Networks</A>
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<A HREF="#E70E104" >Workgroup Networks</A>
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<A HREF="#E70E105" >Departmental Networks</A>
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<A HREF="#E70E106" >Enterprise-Wide Networks</A></UL>
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<A HREF="#E69E239" >Domains, Workgroups, Servers, and Workstations</A>
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<A HREF="#E69E240" >The Topology and Protocols Used in This Chapter's Examples</A>
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<A HREF="#E69E241" >Logging on to Servers and Joining Workgroups</A>
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<A HREF="#E69E242" >Server Redundancy and Backup Systems</A>
<LI>
<A HREF="#E69E243" >Network Adapter Cards and Operating Protocols</A>
<UL>
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<A HREF="#E70E107" >The Network Driver Interface Specification and Network Adapter Card Drivers</A>
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<A HREF="#E70E108" >Network Protocol Stacks Included with Windows NT Server</A>
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<A HREF="#E70E109" >TCP/IP in Windows NT Server 3.51 and Windows NT Workstation 3.51</A>
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<A HREF="#E70E110" >NetBIOS Over TCP/IP and the Windows Sockets API</A></UL>
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<A HREF="#E69E244" >Hubs, Bridges, Routers, and Gateways</A></UL>
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<A HREF="#E68E99" >Maintaining Database Security in a Network Environment</A>
<UL>
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<A HREF="#E69E245" >Network Authority, Permissions, and Accounts</A>
<UL>
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<A HREF="#E70E111" >Security Limitations of Workgroup Networks</A>
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<A HREF="#E70E112" >Supplementing Workgroup Security with Access Database Security Features</A></UL>
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<A HREF="#E69E246" >Network Administrators, Operators, and Users</A>
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<A HREF="#E69E247" >File Permissions Using Windows NT File System Partitions</A></UL>
<LI>
<A HREF="#E68E100" >Fathoming the Access Security System</A>
<UL>
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<A HREF="#E69E248" >Assigning Access User Accounts and Securing Access Databases</A>
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<A HREF="#E69E249" >Securing Existing Database Files</A>
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<A HREF="#E69E250" >Granting and Revoking Access Permissions for Groups and Users</A>
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<A HREF="#E70E113" >Revoking Permissions from the User Group</A>
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<A HREF="#E70E114" >Creating a New Access Group and Assigning Group Permissions</A></UL></UL>
<LI>
<A HREF="#E68E101" >Summary</A></UL></UL></UL>
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<A NAME="E66E49"></A>
<H1 ALIGN=CENTER>
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<FONT SIZE=6 COLOR="#FF0000"><B>- 19 -</B>
<BR><B>Running Visual C++ Database Applications on a Network</B></FONT></CENTER></H1>
<BR>
<P>The majority of Visual C++ databases that you create are likely to be used in a multiuser environment. By definition—at least in the world of PCs running DOS, Windows, or Windows NT, and Macs running System 7+—a multiuser environment requires that all users of a database application be connected by a network in order to share one or more common files. Several surveys conducted in 1993 indicate that about 75 percent of all Windows database applications, excluding terminal-emulation applications for Windows, are installed on networked computers. In 1996, it can be expected that except for home systems and very small business systems, all computers will be networked in the business or commercial environment. Windows terminal-emulation applications, such as Wall Data's Rumba, let you communicate with mainframe computers by simulating a terminal, such as IBM's ubiquitous 3270, in conjunction with a terminal-emulation adapter card, such as DCA's IRMA product line.
<BR>
<P>Developers who are migrating DOS database applications to Visual C++ applications running under Windows (both Windows 95 and Windows NT) need to understand how Windows fits into the network picture. Visual C++ developers whose applications have been limited to single-user products also need a grasp of networking methods and terminology. Access is designed specifically for creating multiuser database applications, but Visual C++ isn't "network-ready" when it comes to such issues as maintaining the security of Access or other desktop database files. Therefore, this chapter begins with a general discussion of network structures, network operating systems and applications, communication protocols, adapter cards, cabling, and other issues that face developers who need to get database applications up and running on a variety of networks. The remainder of this chapter is devoted to network security issues, primarily for desktop database file types.
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<A NAME="E68E98"></A>
<H3 ALIGN=CENTER>
<CENTER>
<FONT SIZE=5 COLOR="#FF0000"><B>Understanding Network Topology and Operations</B></FONT></CENTER></H3>
<BR>
<P>In the world of computers, the term <I>topology</I> describes how computers are connected in a network. Users can be connected to the network by a variety of network interface cards (NICs), network operating protocols, and cables. A local-area network (LAN) consists of computers in a single facility that are connected by some form of cabling. You're not restricted to a copper (wire) or glass (fiber-optic) connection to the network; you also can connect using remote dial-up access through a conventional or cellular telephone equipped with a modem, a leased telephone line, a low-power wireless (radio-frequency or RF) connection, or even a satellite link. LANs in different locations can be connected into wide-area networks (WANs) by high-speed telephone lines using T1, ISDN, or ATM hardware and communication protocols. The concentrators, routers, bridges, gateways, and protocols that are used to create WANs are discussed later in this chapter. Both Windows 95 and Windows NT support dial-in network connections, which can provide usable performance when high-speed (28K or greater) modems are used.
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<BLOCKQUOTE>
<BLOCKQUOTE>
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<BR>
<NOTE><B>NOTE</B>
<BR>
<BR>In late 1995, AT&T Paradyne introduced a new technology that makes it possible to transfer 6Mbps of data through ordinary copper phone lines. Dubbed GlobeSpan, this AT&T system uses an asymmetric digital subscriber line modem to achieve these speeds without requiring telephone companies to install a new infrastructure of fiber-optic and coaxial cable. If everything works as AT&T plans, all this high-speed bandwidth will be made accessible inexpensively by the end of 1996. AT&T says GlobeSpan could be available in most parts of the country at rates that are comparable to standard phone service.</NOTE>
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<HR ALIGN=CENTER>
</BLOCKQUOTE></BLOCKQUOTE>
<P>The following sections describe the topology of workgroup and client-server networks, the inner workings of a newly upgraded network operating system (Windows NT Server 3.5), and Transmission Control Protocol/Internet Protocol (TCP/IP), which has become a <I>de facto</I> industry standard for implementing wide-area PC networks.
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<BR>
<A NAME="E69E238"></A>
<H4 ALIGN=CENTER>
<CENTER>
<FONT SIZE=4 COLOR="#FF0000"><B>The Scope of PC Networks</B></FONT></CENTER></H4>
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<P>The primary classification of networks is by scope. The <I>scope</I> of a network is determined by the number and proximity of the computers connected to the network. The basic network scope classifications—workgroup, departmental, and enterprise-wide—are described in the following sections.
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<BR>
<A NAME="E70E104"></A>
<H5 ALIGN=CENTER>
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