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  • 1C H A P T E R O N E Introduction to


    Objectives 2.3 Identify common physical network topologies

    . Star

    . Mesh

    . Bus

    . Ring

    . Point to point

    . Point to multipoint

    . Hybrid

    2.7 Explain common logical network topologies and their char- acteristics

    . Peer-to-peer

    . Client/server

    . VPN

    . VLAN

    What You Need to Know . Understand the differences between local area networks (LANs), wide area

    networks (WANs), and personal area networks (PANs).

    . Identify the characteristics between peer-to-peer and client/server network- ing.

    . Identify the characteristics of various network topologies.

  • 14

    Chapter 1: Introduction to Networking

    Introduction A variety of physical and logical network layouts are in use today. As a network administrator, you might find yourself working on these different network lay- outs or topologies. Therefore, you will need to understand how they are designed to function.

    This chapter reviews general network considerations such as the various topolo- gies used on today’s networks, LANs, PANs, and WANs, and the Institute of Electrical and Electronics Engineers (IEEE) standards.

    LANs, WANs, MANs, and WPANs Networks are classified according to their geographic coverage and size. The two most common network classifications are local area networks (LANs) and wide area networks (WANs).

    LANs A LAN is a data network that is restricted to a single geographic location and typi- cally encompasses a relatively small area, such as an office building or school. The function of the LAN is to interconnect workstation computers for the purpose of sharing files and resources. Because of its localized nature, the LAN typically is high speed and cheaper to set up than a WAN. Figure 1.1 shows an example of a LAN.

    Network Attached Printer


    PC PC PC

    PC PC PC

    Ethernet Switches

    FIGURE 1.1 A local area network.

  • LANs, WANs, MANs, and WPANs 15

    WANs A WAN is a network that spans more than one geographic location, often con- necting separated LANs. WANs are slower than LANs and often require addi- tional and costly hardware such as routers, dedicated leased lines, and compli- cated implementation procedures. Figure 1.2 shows an example of a WAN.

    Server PC



    Ethernet Switch




    Router Ethernet Switch Server

    New York


    Ethernet Switch Server


    FIGURE 1.2 A wide area network.

    Metropolitan Area Networks (MANs) A MAN is confined to a certain geographic area, such as a university campus or city. No formal guidelines dictate the differences between a MAN and a WAN; technically, a MAN is a WAN. Perhaps for this reason, the term MAN is used less frequently than WAN. If any distinction exists, it’s that a MAN is smaller than a WAN. A MAN is almost always bigger than a LAN and usually is small- er than or equal to a WAN. MANs utilize an Internet service provider (ISP) or telecommunications (telco) provider.

    WPANs Wireless technologies have introduced a new term—wireless personal area net- work (WPAN). WPAN refers to the technologies involved in connecting devices in very close proximity to exchange data or resources. An example is connecting a laptop with a PDA to synchronize an address book. Because of their small size and the nature of the data exchange, WPAN devices lend them-

  • 16

    Chapter 1: Introduction to Networking

    selves well to ad hoc wireless networking. Ad hoc wireless networks are those that have devices connect to each other directly, not through a wireless access point. Ad hoc wireless networks are discussed later in this chapter.

    Because of the close proximity of WPAN networking, short-range wireless tech- nologies typically are used. This includes Bluetooth and infrared, both of which are supported by major operating systems, including Windows, Linux, and Macintosh. Wireless technologies are discussed in detail in Chapter 7, “Wireless Networking.”

    Network Models You can choose from two basic wired network models—peer-to-peer and client/server. The model used for a network is determined by several factors, including how the network will be used, how many users will be on the network, and budgetary considerations.

    Peer-to-Peer Networking Model A peer-to-peer network is a decentralized network model offering no central- ized storage of data or centralized control over the sharing of files or resources. All systems on a peer-to-peer network can share the resources on their local computer as well as use resources of other systems.

    Peer-to-peer networks are cheaper and easier to implement than client/server networks, making them an ideal solution for environments in which budgets are a concern. The peer-to-peer model does not work well with large numbers of computer systems. As a peer-to-peer network grows, it becomes increasingly complicated to navigate and access files and resources connected to each com- puter, because they are distributed throughout the network. Furthermore, the lack of centralized data storage makes it difficult to locate and back up key files.

    Peer-to-peer networks typically are found in small offices or residential settings where only a limited number of computers will be attached and only a few files and resources shared. A general rule of thumb is to have no more than 10 com- puters connected to a peer-to-peer network.

    Client/Server Networking Model The client/server networking model is, without question, the most widely implemented model and the one you are most likely to encounter when work- ing in real-world environments. The advantages of the client/server system stem from the fact that it is a centralized model. It allows for centralized network

  • Network Models 17

    management of all network services, including user management, security, and backup procedures.

    A client/server network often requires technically skilled personnel to imple- ment and manage the network. This and the cost of dedicated server hardware and software increase the cost of the client/server model. Despite this, the advantages of centralized management, data storage, administration, and securi- ty make it the network model of choice.

    Comparing Peer-to-Peer and Client/Server Network Models Table 1.1 summarizes the characteristics of the peer-to-peer and client/server network models.

    EXAM ALERT The role of the client computer in the client/server model is to request the data from the server and present that data to the users.

    Table 1.1 Comparison of Networking Models Attribute Peer-to-Peer Network Client/Server Network

    Size Recommended to a maximum The size of the network is of 10 computers. limited only by server size,

    network hardware, and budget. It can have thousands of connected systems.

    Administration Each individual is responsible A skilled network administrator for the administration of his is often required to maintain or her own system. An and manage the network. administrator is not needed.

    Security Each individual is responsible Security is managed from a for maintaining security for central location but often local files and devices requires a skilled administrator connected to the system. to correctly configure.

    Cost Minimal startup and Requires dedicated equipment implementation cost. and specialized hardware and

    administration, increasing the network’s cost.

    Implementation Easy to configure and set up. Often requires complex setup pro- cedures and skilled staff to set up.

  • 18

    Chapter 1: Introduction to Networking

    Centralized and Distributed Computing The terms centralized and distributed computing are used to describe where the network processing takes place. In a centralized computing model, one system provides both the data storage and processing power for client systems. This networking model is most often associated with computer mainframes and dumb terminals, where no processing or storage capability exists at the worksta- tion. These network environments are rare, but they do still exist.

    A distributed network model has the processing power distributed between the client systems and the server. Most modern networks use the distributed net- work model, where client workstations share in the processing responsibilities.

    Virtual Private Networks (VPNs) In the mid-1990s, Microsoft, IBM, and Cisco began working on a technology called tunneling. By 1996, more companies had become interested and involved in the work. From their efforts, virtual private networks (VPNs) became one of the most popular methods of remote access. But before we can know why VPNs became so popular, we must know a bit more about them.

    NOTE Why now? The CompTIA objectives specify that VPNs and VLANs are to be discussed in this section. These are covered here to make the objective complete; they also are dis- cussed in other areas of the book.

    Essentially, a VPN extends a LAN by establishing a remote connection using a public network such as the Internet. A VPN provides a point-to-point dedicat- ed link between two points over a public IP network. Figure 1.3 shows how a VPN enables remote access for a remote client to a private network.

    For many companies, the VPN link provides the perfect method to expand their networking capabilities and reduce their costs. By using the public network (Internet), a company does not need to rely on expensive private leased lines to provide corp