Networks are classified into two major categories – LANs and WANs – based on the devices and areas in which they interconnect.
Local Area Networks
A LAN is a localized computerized network used to communicate between host systems, generally for sharing information (e.g., documents, audio files, video files, e-mail, and chat messages) and using a wide variety of productivity tools.
LANs have limited reach, as their name implies, spanning across an area less than a few hundred meters, so they only can connect devices in the same building or campus. Local Area Connections usually belong to the companies in which they are deployed. The different LAN technologies available include the following:
- Ethernet (10 Mbps)
- FastEthernet (100 Mbps)
- GigabitEthernet (1 Gbps)
- Wireless LAN (up to 600 Mbps under the 802.11n specification)
All the network devices in a LAN have a common logical addressing scheme and all the devices share the same network address (IP address). An example of an IP address is 192.168.10.0, with devices having logical addresses such as 192.168.10.1, 192.168.10.2, and so on. IP addressing will be discussed later in this chapter.
Figure 1.8 – Local Area Network Components
Generally, network devices such as workstations, IP telephones, printers, plotters, laptops, servers, and PDA devices connect to an Access Layer switch via either a wired or a wireless network, as shown above in Figure 1.8. The Access Layer switch may have a higher speed link to a router, which may connect to other routers or have an outbound Internet connection. Anything behind the router is part of the WAN, so the router serves as an edge device between a LAN and a WAN.
Wide Area Networks
Understanding how to implement and design WANs is an important step toward becoming a networking professional, a position in which you will find various ways to connect different systems, whether you are working in a small campus area, a large campus network, a metropolitan area, or a global network. As mentioned, a WAN connects multiple LANs or multiple WANs (e.g., the Internet is a large WAN, or a network of networks). A WAN is usually located over a broad geographical area and belongs to an Internet Service Provider (ISP) that might charge a fee for using its WAN services. Because of its size, a typical WAN is slower than a LAN.
Figure 1.9 – Example of a Wide Area Network
As shown in Figure 1.9 above, the ISP serves as a network that covers a specific area and interconnects different local networks, such as between a home office and a branch office of the same company, or a branch office and a headquarters of different companies. WANs use a wide variety of protocols and topologies to accomplish this interconnecting of different LAN areas, which will be covered in detail in Chapter 5.
LAN connections to the ISP can take many forms, depending on the technology in use, such as the following:
- Packet-switched networks (Frame Relay), where the ISP creates permanent virtual circuits and switched virtual circuits that carry data between subscriber sites
- Circuit-switched networks (ISDN), where the ISP creates a physical path reserved for the duration of the connection between two sites
- T1/E1 lines
- Leased lines, using PPP or HDLC protocols
- Dial-up connections
- Cable, using cable television networks to deliver data
- DSL, utilizing traditional copper telephone lines to deliver data
WANs and LANs use specific routing protocols that are configured based on topology and other criteria. The various routing protocols will be covered in detail in subsequent chapters.