A computer network is a system that connects computers and other devices (e.g., printers) via communications media so that data and information can be transmitted among them. Voice and data communication networks are continually becoming faster that is, their bandwidth is increasing and cheaper. Bandwidth refers to the transmission capacity of a network; it is stated in bits per second.
The broadband industry itself has diffi culty defi ning the term, broadband. The Federal Communications Commission originally defi ned broadband as the transmission capacity of a communications medium (discussed later in this chapter) faster than 256,000 (256 Kbps) bits per second. The FCC then upgraded its defi nition to 768 Kbps downstream (e.g., downloading a syllabus from your university’s network) and 256 Kbps upstream (e.g., uploading content to Facebook). In 2010, the FCC upgraded its defi nition of broadband to 4 Mbps (million bits per second) downstream and 1 Mbps upstream. In 2013, the FCC says that it is considering another defi nitional upgrade for broadband. Therefore, we defi ne broadband as the transmission capacity of a communications medium faster than 4 Mbps downstream and 1 Mbps upstream. The defi nition of broadband is fl uid, and will undoubtedly be changed to refl ectlarger transmission capacities in the future.
You are familiar with certain types of broadband connections, such as digital subscriber line (DSL) and cable to your homes and dorms. DSL and cable fall within the range of transmission capacity mentioned here and are thus defi ned as broadband connections. The various types of computer networks range from small to worldwide. They include (from smallest to largest) personal area networks (PANs), local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), and the Internet. PANs are short-range networks typically a few meters that are used for communication among devices close to one person. PANs can be wired or wireless. (You will learn about wireless PANs in Chapter 8.) MANs are relatively large computer networks that cover a metropolitan area. MANs fall between LANs and WANs in size. WANs typically cover large geographic areas; in some cases they can span the entire planet.
Local Area Networks
Regardless of their size, networks represent a compromise among three objectives: speed, distance, and cost. Organizations typically must select two of the three. To cover long distances, organizations can have fast communication if they are willing to pay for it, or cheap communication if they are willing to accept slower speeds. A third possible combination of the three trade-offs is fast, cheap communication with distance limitations. This is the idea behind local area networks. A local area network (LAN) connects two or more devices in a limited geographical region, usually within the same building, so that every device on the network can communicate with
The broadband industry itself has diffi culty defi ning the term, broadband. The Federal Communications Commission originally defi ned broadband as the transmission capacity of a communications medium (discussed later in this chapter) faster than 256,000 (256 Kbps) bits per second. The FCC then upgraded its defi nition to 768 Kbps downstream (e.g., downloading a syllabus from your university’s network) and 256 Kbps upstream (e.g., uploading content to Facebook). In 2010, the FCC upgraded its defi nition of broadband to 4 Mbps (million bits per second) downstream and 1 Mbps upstream. In 2013, the FCC says that it is considering another defi nitional upgrade for broadband. Therefore, we defi ne broadband as the transmission capacity of a communications medium faster than 4 Mbps downstream and 1 Mbps upstream. The defi nition of broadband is fl uid, and will undoubtedly be changed to refl ectlarger transmission capacities in the future.
You are familiar with certain types of broadband connections, such as digital subscriber line (DSL) and cable to your homes and dorms. DSL and cable fall within the range of transmission capacity mentioned here and are thus defi ned as broadband connections. The various types of computer networks range from small to worldwide. They include (from smallest to largest) personal area networks (PANs), local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), and the Internet. PANs are short-range networks typically a few meters that are used for communication among devices close to one person. PANs can be wired or wireless. (You will learn about wireless PANs in Chapter 8.) MANs are relatively large computer networks that cover a metropolitan area. MANs fall between LANs and WANs in size. WANs typically cover large geographic areas; in some cases they can span the entire planet.
Local Area Networks
Regardless of their size, networks represent a compromise among three objectives: speed, distance, and cost. Organizations typically must select two of the three. To cover long distances, organizations can have fast communication if they are willing to pay for it, or cheap communication if they are willing to accept slower speeds. A third possible combination of the three trade-offs is fast, cheap communication with distance limitations. This is the idea behind local area networks. A local area network (LAN) connects two or more devices in a limited geographical region, usually within the same building, so that every device on the network can communicate with
every other device. Most LANs today use Ethernet. Figure 6.1 illustrates an Ethernet LAN that consists of four computers, a server, and a printer, all of which connect via a shared cable. Every device in the LAN has a network interface card (NIC) that allows the device to physically connect to the LAN’s communications medium. This medium is typically unshielded twisted-pair wire (UTP). Although it is not required, many LANs have a fi le server or network server. The server typically contains various software and data for the network. It also houses the LAN’s network operating system, which manages the server and routes and manages communications on the network.
Wide Area Networks
When businesses have to transmit and receive data beyond the confi nes of the LAN, they use wide
area networks. Interestingly, the term wide area network did not even exist until local area networks appeared. Before that time, what we call a wide area network today was simply called a “network.” A wide area network (WAN) is a network that covers a large geographic area. WANs typically connect multiple LANs. They are generally provided by common carriers such as telephone companies and the international networks of global communications services providers. WANs have large capacity, and they typically combine multiple channels (e.g., fi beroptic cables, microwave, and satellite). The Internet is an example of a WAN. WANs also contain routers. A router is a communications processor that routes messages from a LAN to the Internet, across several connected LANs, or across a wide area network such as the Internet.
Wide Area Networks
When businesses have to transmit and receive data beyond the confi nes of the LAN, they use wide
area networks. Interestingly, the term wide area network did not even exist until local area networks appeared. Before that time, what we call a wide area network today was simply called a “network.” A wide area network (WAN) is a network that covers a large geographic area. WANs typically connect multiple LANs. They are generally provided by common carriers such as telephone companies and the international networks of global communications services providers. WANs have large capacity, and they typically combine multiple channels (e.g., fi beroptic cables, microwave, and satellite). The Internet is an example of a WAN. WANs also contain routers. A router is a communications processor that routes messages from a LAN to the Internet, across several connected LANs, or across a wide area network such as the Internet.
Enterprise Networks
Organizations today have multiple LANs and may have multiple WANs. All of these networks are interconnected to form an enterprise network. Figure 6.2 displays a model of enterprise computing. Note that the enterprise network in the fi gure has a backbone network. Corporate backbone networks are high-speed central networks to which multiple smaller networks (such as LANs and smaller WANs) connect. The LANs are called embedded LANs because they connect to thebackbone WAN.
Organizations today have multiple LANs and may have multiple WANs. All of these networks are interconnected to form an enterprise network. Figure 6.2 displays a model of enterprise computing. Note that the enterprise network in the fi gure has a backbone network. Corporate backbone networks are high-speed central networks to which multiple smaller networks (such as LANs and smaller WANs) connect. The LANs are called embedded LANs because they connect to thebackbone WAN.
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