Data Communications and Internet Technology

1. Data Communications and Internet Technology

2. Fundamental Networking Concepts • A computer network is a collection of computers that communicate with one another over transmission lines. • Three basic types of networks are: • Local area networks (LANs)–connects computers that reside in a single geographic location on the premises of the company that operates the LAN. • Wide area networks (WANs)–connects computers at different geographic sites. • Internets–a network of networks

3. Fundamental Networking Concepts (Continued) • The networks that comprise an Internet use a large variety of communication methods and conventions, and data must flow seamlessly across them. • To provide seamless flow, an elaborate scheme called a layered protocol is used.

4. Figure 5-1 Major Network Types

5. Figure 5-2 Example Networks

6. Communications Protocols • A protocol is a standard means for coordinating an activity between two or more entities. • A communications protocol is a means for coordinating activity between two or more communicating computers. • Two machines must agree on the protocol to use, and they must follow that protocol as they send messages back and forth. • Communications protocols are broken into levels of layers.

7. Figure 5-5 TCP/IP-OSI on Your Computer

8. Layer 4 • An email program (which uses SMTP) interacts with another protocol called TCP, or Transmission Control Program (TCP).

9. Local Area Networks • A local area network (LAN) is a group of computers connected together on a single company site. • Usually the computers are located within a half mile or so of each other, although longer distances are possible. • The key distinction, however, is that all of the computers are located on property controlled by the company that operates the LAN. • Computers and printers are connected via a switch, which is a special-purpose computer that receives and transmits messages on the LAN.

10. Local Area Networks (Continued) • Each device on a LAN (computer, printer, etc.) has a hardware component called a network interface card (NIC) that connects the device’s circuitry to the cable. • The NIC works with programs in each device to implement Layer 1 and Layer 2 protocols. • Each NIC has a unique identifier, which is called the (MAC) media access control address. • The computers, printers, switches, and other devices on a LAN are connected using one of two media. • Most connections are made using unshielded, twisted pair (UTP) cable. • A device called an RJ-45 connector is used to connect the UTP cable into NIC devices on the LAN.

11. Figure 5-6 Local Area Network

12. LANs with Wireless Connections • Wireless connections have become popular with LANs. • The NIC for wireless devices have been replaced by wireless NIC (WNIC). • For laptop computers, such devices can be cards that slide into the PCMA slot or they can be built-in, onboard devices. • Several different wireless standard exist • As of 2005, the most popular is IEEE 802.11g • The current standard, 802.11g allows speeds of up to 54 Mbps. • The WNICs operate according to the 802.11 protocol and connect to an access point (AP).

13. Figure 5-10

14. Wide Area Networks • A wide area network (WAN) connects computers located at physically separated sites. • A company with offices in Detroit and Atlanta must use a WAN to connect the computers together. • Because the sites are physically separated, the company cannot string wire from one site to another. • An Internet service provider (ISP) has three important functions: • It provides you with a legitimate Internet address. • It serves as your gateway to the Internet. • It receives the communication from your computer and passes them on to the Internet, and it receives communication from the Internet and passes them on to you.

15. DSL Modems • A DSL modem is takes the place of a cable connection. • DSL stands for digital subscriber line. • DSL modems operate on the same lines as voice telephones and dial-up modems. • They operate so that their signals do not interfere with voice telephone service. • They provide much faster data transmission speeds than dial up modems. • They always maintain a connection.

16. Virtual Private Network • Virtual private network (VPN) is the fourth WAN alternative. • A VPN uses the Internet or a private internet to create the appearance of private point-to-point connections. • A VPN uses the public Internet to create the appearance of a private connection. • A connection called a tunnel, is a virtual pathway over a public or shared network from the VPN client to the VPN server.

17. Virtual Private Network (Continued) • VPN communications are secure. • The VPN client software encrypts, or codes, the original messages so that its contents are hidden. • Virtual private networks offer the benefit of point-to-point leased lines, and they enable remote access, both by employees and by any others who have been registered with the VPN server.

18. Figure 5-18 Remote Access Using VPN: Actual Connections

19. Domain Name System • IP addresses are useful for computer-to-computer communication, but they are not well suited for human use. • The purpose of the domain name system (DNS) is to convert user-friendly names into their IP addresses. • Any registered, valid name is called a domain name. • The process of changing a name into its IP address is called resolving the domain name.