There are two fundamentally different types of telecommunications networks: telephone networks and computer networks, which are slowly merging into a single digital network using shared Internet technology and equipment.

Both voice and data communication networks have also become more powerful (faster), more portable (smaller and mobile), and less expensive. Today more than 60 percent of U.S. Internet users have high-speed broadband connections provided by telephone and cable TV companies running at one million bits per second. The cost for this service has fallen exponentially. Increasingly, voice and data communication as well as Internet access are taking place over broadband wireless platforms.

In addition to client computers, the major components used in a simple network include:

• Network interface cards (NICs): Typically built into client computers
  
  
• Connection medium: Cables or wireless signals for transmitting data
  
  
• Network operating system (NOS): Software that manages communications on the network and coordinates network resources, and can reside on every computer or on a dedicated server computer
  
  
• Hub or switch: Hubs are devices that connect network components, sending packets of data to all connected devices. Switches are like hubs but can forward data to specific destinations.
  
  
• Routers are network devices to connect two or more networks

Figure 7-1

FIGURE 7-1 COMPONENTS OF A SIMPLE COMPUTER NETWORK Illustrated here is a very simple computer network, consisting of computers, a network operating system residing on a dedicated server computer, cable (wiring) connecting the devices, network interface cards (NIC), switches, and a router.

Large corporate network infrastructure typically consists of small local-area networks (LANs) linked to firm-wide corporate networks for data and voice communication, and various powerful servers, for supporting corporate Web sites, an intranet, extranets, or connecting to backend systems such as sales, ordering, and financial transactions. Corporations face the problem of integrating these networks, a task becoming easier as communications become digital.

Figure 7-2

FIGURE 7-2 CORPORATE NETWORK INFRASTRUCTURE Today’s corporate network infrastructure is a collection of many different networks from the public switched telephone network; to the Internet; to corporate local-area networks linking workgroups, departments, or office floors.

Contemporary digital networks are based on three key technologies:

1. Client/server computing: In client/server computing, client computers are linked to each other through a network controlled by a server computer, which sets the rules of communication for the network and provides addresses for each client and device on the network.
   
   
2. Packet switching: A method of breaking messages into small packets that are sent independently along different paths in a network using a router and then reassembled at their destination.

Figure 7-3

FIGURE 7-3 PACKED-SWITCHED NETWORKS AND PACKET COMMUNICATIONS Data are grouped into small packets, which are transmitted independently over various communications channels and reassembled at their final destination.

3. Common protocols and TCP/IP: Widely used communications protocols provide a set of rules to enable communication among diverse components in a telecommunications network. TCP/IP is a suite of protocols which has become the dominant model of achieving connectivity among different networks and computers and on the Internet, providing a method for breaking up messages into packets, routing them to the proper address, and reassembling them. The TCP/IP reference model has four layers. Two computers using TCP/IP can communicate even if they are based on different hardware and software platforms.

Figure 7-4

FIGURE 7-4 THE TRANSMISSION CONTROL PROTOCOL/INTERNET PROTOCOL (TCP/IP) REFERENCE MODEL This figure illustrates the four layers of the TCP/IP reference model for communications.