Cell phone layouts

     One of the most explosive areas of growth in recent years has been cell phone networks. Figure 1-10 shows an example of a handheld PDA that, along with making telephone calls, can transmit and receive data. The PDA has a modem installed, which transmits the PDA’s data across the cell phone network to the cell phone switching center. The switching center then transfers the PDA’s data over the public telephone network or through a connection onto the Internet. Many newer handheld devices have combined data accessing capabilities with a cell phone and can transfer data over cell phone connections.

An example of a user with a smart cell phone transmitting and receiving data

Satellite and microwave layouts

     Satellite and microwave layouts are continuously evolving technologies used in a variety of applications. If the distance between two networks is great and running a wire between them would be difficult (if not impossible), satellite and microwave transmission systems can be an extremely effective way to connect the two networks or computer systems. Examples of these applications include digital satellite TV, meteorology, intelligence operations, mobile maritime telephony, GPS navigation systems, wireless e-mail, worldwide mobile telephone systems, and video conferencing. Figure 1-9 shows a diagram of a typical satellite system.

Example of a television company using a satellite system to broadcast television services into homes and businesses

Sensor to local area network layouts

     Another common layout found in everyday life is the sensor-to-local area network layout. In this type of layout, the action of a person or object triggers a sensor—for example, a left-turn light at a traffic intersection—that is connected to a network. In many left-turn lanes, a separate left-turn signal will appear if and only if one or more vehicles are in the left-turn lane. A sensor embedded in the roadway detects the movement of an automobile in the lane above and triggers the left-turn mechanism in the traffic signal control box at the side of the road. If this traffic signal control box is connected to a larger traffic control system, the sensor is connected to a local area network.


     Another example of sensor-to-local area network layout is found within manufacturing environments. Assembly lines, robotic control devices, oven temperature controls, and chemical analysis equipment often use sensors connected to data-gathering computers that control movements and operations, sound alarms, and compute experimental or quality control results. Figure 1-8 shows a diagram of a typical sensor-to-local area network layout in a manufacturing environment.

An automobile moves down an assembly line and triggers a sensor

Wide area network to wide area network layouts

     The Internet is not a single network but a collection of thousands of networks. In order to travel any distance across the Internet, a data packet undoubtedly will pass through multiple wide area networks. Connecting a wide area network to a wide area network requires special devices that can route data traffic
quickly and efficiently. These devices are high-speed routers. After the data packet enters the high-speed router, an address in the network layer (the IP address) is extracted, a routing decision is made, and the data packet is forwarded on to the next wide area network segment. As the data packet travels across the Internet, router after router makes a routing decision, moving the data toward its final destination. We will examine the Internet in more detail in Chapter Ten, then follow up with a discussion of several other types of wide area network technologies in Chapter Eleven.

Local area network to wide area network layouts

     You have already seen that the local area network is commonly found in business and academic environments. If a user working at a microcomputer connected to a local area network wishes to access the Internet (a wide area network), the user’s local area network must have a connection to the Internet. A device called a router is employed to connect these two networks. A router converts the local area network data into wide area network data. It also performs security functions and must be properly programmed to accept or reject certain types of incoming and outgoing data packets. Figure 1-7 shows a local area network connected to a wide area network via a router.

Local area network to wide area network layout

Local area network to metropolitan area network layouts

     Toward the end of the twentieth century, a new form of network appeared that interconnected businesses within a metropolitan area. Typically, this interconnection uses only fiber-optic links at extremely high speeds. These new networks are labeled metropolitan area networks. A metropolitan area network is a highspeed
network that interconnects multiple sites within a close geographic region, such as a large urban area. For example, businesses that require a high-speed connection to their Internet service providers might use a metropolitan area network for interconnection (see Figure 1-6). As we shall see in more detail in Chapter Nine, metropolitan area networks are a cross between local area networks and wide area networks. They can transfer data at fast LAN speeds but over larger geographic regions than typically associated with a local area network.

Businesses interconnected within a large metropolitan area via a metropolitan area network

Personal area network to workstation layouts

     The personal area network was created in the late 1990s and is one of the newer forms of computer networks. Using wireless transmissions with devices such as personal digital assistants (PDAs), laptop computers, and portable music players, an individual can transfer voice, data, and music from handheld devices to other devices such as microcomputer workstations (see Figure 1-5). Likewise, a user can download data from a workstation to one of these portable devices. For example, a user might use a PDA to record notes during a meeting. Once the meeting is over, the user can transmit the notes over a wireless connection from the PDA to his or her workstation. The workstation then runs a word processor to clean up the notes, and the formatted notes are uploaded to a local area network for corporate dissemination. Another example is the hands-free Bluetooth-enabled connection that people hang on their ear so they can converse with their cell phone without placing the cell phone up to their ear. It is also very common now to transfer digital photos and videos from cameras to microcomputers using short-range, wireless signals.

A user transferring data from a personal digital assistant via a personal area network to a workstation attached to a local area network