In most cases, the elements of a network infrastructure are both inherited and designed. If you are building a network that will be connected to the Internet, for example, certain aspects of the network, such as the use of the TCP/IP protocol suite, are inherited from the Internet. Other network elements, such as the physical layout of basic network compo nents, are chosen by design when the network is first conceived and are then inherited by later versions of the network as it evolves. It is rare for an engineer to have the opportunity to design a network from scratch, with no pre-existing influences. Nearly always, the engi neer must incorporate some existing elements into the network design, such as specific applications, operating systems, protocols, or hardware components.
Implementing a network infrastructure is the process of evaluating, purchasing, and assembling the specified components, and installing them in the manner prescribed by the design plan. The implementation process begins with engineers installing the net- work’s hardware infrastructure, including computers, cables, and connectivity devices such as hubs, switches, and routers, as well as printers and other peripherals. Once the hardware is in place, the engineers install and configure the operating systems, appli cations, and other software.
The operating systems running on the computers are the primary software components in the network infrastructure, because they incorporate the protocols and other rou tines that make network communications possible. In addition to the standard commu nication protocols common to all network operating systems, the Microsoft Windows
Server 2003 family also includes a collection of applications and services that imple ment important security and special communications capabilities on the network. The significance of the network infrastructure does not end when the construction of the network is complete, however. The personnel responsible for maintaining the net- work must have an intimate knowledge of the network’s infrastructure to expand the network, perform upgrades, and troubleshoot problems. The 70-293 exam tests your knowledge of how the infrastructure affects the planning, implementation, and main tenance of a medium-to-large network, and of how Windows Server 2003 functions as a part of that infrastructure.
Physical Infrastructure
A network’s physical infrastructure is its topology—the physical design of the network— along with hardware components such as cabling, routers, switches, hubs, servers, and workstations. The hardware you select when planning the network’s physical infra structure is frequently dependent on elements of the network’s logical infrastructure. For example, if you decide to use Ethernet for your network’s data-link layer protocol, you are limited to certain specific cable types supported by Ethernet, and the network’s connectivity components—hubs, routers, and switches— must be designed for use with Ethernet as well.
For a small network, the physical infrastructure can be very simple—computers, a hub, and a few cables are generally all you need. For medium-to-large networks, however, the physical infrastructure can be extraordinarily complex. In addition to a large fleet of computers, a vast system of cables, and multiple interconnected hubs, the network might require routers or switches to connect segments, plus the additional components needed to support Internet connections, remote client access, wide area connections to other sites, or wireless connectivity.
The hardware used to implement these additional technologies is various and always relates to the network’s logical infrastructure. For example, to connect the Ethernet local area network (LAN) in the company headquarters to the Ethernet LAN in a branch office, you must choose a different data-link layer protocol for the wide area network (WAN) connection (such as Point-to-Point Protocol), as well as a different network medium (such as a dial-up or a T-1 connection), and you must be sure that the hard- ware and software on both LANs support the WAN technology you choose.
See Also For more information on WAN connections, see Lesson 1 in Chapter 3, “Planning Internet Connectivity,” and Lesson 1 in Chapter 5, “Using Routing and Remote Access.”
Exam Tip Familiarity with the physical infrastructure of a network is prerequisite knowledge for the 70-293 exam. You should be familiar with the functions of all the basic hardware com ponents and how to connect them to construct a network.
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Logical Infrastructure
A network’s logical infrastructure comprises the many software elements that connect, manage, and secure hosts on the network. The logical infrastructure allows communi cation between computers over the pathways described in the physical topology. The logical infrastructure of a network consists of both abstract software elements, such as networking protocols, and concrete elements, such as specific software products. For example, when designing the infrastructure for a medium-to-large network, you will probably decide to use the TCP/IP protocols for network and transport-layer com munications. At this stage of planning, TCP/IP is considered to be an abstract element because you can implement the protocols using any one of several software products. After deciding on the abstract element, you must also select the concrete element you will use to implement that abstract element. After deciding to use TCP/IP, for example, you might then select the TCP/IP implementation found in the Microsoft Windows operating systems.
In addition to basic communication protocols such as TCP/IP, the abstract elements of the logical infrastructure can include security technologies such as digital certificates and the IP Security (IPSec) protocols. Various types of concrete elements can imple ment these abstract elements.
Planning For a network based on Windows Server 2003, most concrete elements needed in a typical infrastructure are realized in the operating system itself. In other cases, you might need to implement protocols and abstract security components as separate software products.
Windows Server 2003 includes a large number of optional protocols and services, and deciding which of those protocols and services you want to use is also part of the log ical infrastructure design process. In some cases, you might decide to use a third-party product rather than an operating system component. For example, Windows Server 2003 includes a backup software program of its own, but you might decide one of the other network backup software products on the market offers additional features that you need.