Data Network Types

Data networks are most commonly classified as local area networks (LANs) and wide area networks (WANs). You should understand the fundamental distinctions between these two network classifications.

Local area network (LAN)

A local area network (LAN) is a data network that operates across a relatively small geographic area, such as a single building or floor. A LAN connects workstations, servers, printers, and other devices so that network resources, such as files and e-mail, can be shared. Key characteristics of LANs include the following:

Can connect networked resources over a small geographic area, such as a floor, a building, or a group of buildings.

Are relatively inexpensive to set up and maintain, typically consisting of readily available equipment such as servers, client workstations or PCs, printers, switches, hubs, bridges, repeaters, wireless access points (WAPs or simply, APs), and various security devices.

Can be wired, wireless, or a combination of both wired and wireless.

Perform at relatively high speeds — typically 10 megabits per second (Mbps), 100 Mbps, or 1000 Mbps (also referred to as 1 gigabit per second [1 Gbps]) for wired networks, and 11or 54 Mbps for wireless networks. In high-performance datacenters and storage area networks (SANs), 10 Gbps speeds are also becoming more common. We cover LAN speeds in the section “Physical Layer (Layer 1),” later in this chapter.

Be careful when referring to data speeds (and their abbreviations) and data storage. 100 Mbps is “100 megabits per second,” and 100 MB is “100 megabytes.” The distinction is subtle (a little b versus a big B, bits rather than bytes), but the difference is significant: A byte is equal to 8 bits. Data speeds are typically referred to in bits per second; data storage is typically referred to in bytes.

A local area network (LAN) is a data network that operates across a relatively small geographic area.

See the section “The OSI Reference Model,” later in this chapter, for a discussion of the LAN function at the Physical and Data Link layers of the OSI Reference Model.

Wide area network (WAN)

A wide area network (WAN) connects multiple LANs and other WANs by using telecommunications devices and facilities to form an internetwork. Key characteristics of WANs include the following:

Connect multiple LANs over large geographic areas, such as a small city (for example, a metropolitan area network [or MAN]), a region or country, a global corporate network, the entire planet (for example, the Internet), or beyond (for example, the International Space Station via satellite).

Can be relatively expensive to set up and maintain, typically consisting of equipment such as routers, Channel Service Unit/Data Service Unit (CSU/DSU) devices, firewalls, Virtual Private Network (VPN) concentrators, and various other security devices.

Perform at relatively low speeds by using various technologies, such as dial-up (56 kilobits per second [Kbps]); digital subscriber line, or DSL (for example, 128 Kbps to 3 Mbps); T-1 (1.544 Mbps); DS-3 (45 Mbps); OC-12 (622 Mbps); and OC-255 (13 Gbps). We cover WAN speeds in the section “Data Link Layer (Layer 2),” later in this chapter.

Examples of WANs include

Internet: The mother of all WANs, the Internet is the global network of public networks originally developed by the U.S. Department of Defense (DoD) Advanced Research Projects Agency (ARPA). Users and systems connect to the Internet via Internet service providers (ISPs).

Intranet: An intranet can be thought of as a private Internet. An intranet typically uses web-based technologies to disseminate company information that’s available only to authorized users on the company network.

Extranet: An extranet extends the basic concept of an intranet to include partners, vendors, or other related parties. For example, an automobile manufacturer may operate an extranet that connects networks belonging to parts manufacturers, distributors, and dealerships. Extranets are commonly operated across the Internet by using a Virtual Private Network (VPN) — discussed in the section “Virtual Private Networks (VPNs),” later in this chapter — or other secure connection.

See the following section for a discussion of the WAN function at the Physical, Data Link, and Network layers of the OSI Reference Model.

A wide area network (WAN) is a data network that operates across a relatively large geographic area.