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Embed code for: 16.2 Internet Connectivity
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16.2 Internet Connectivity
Internet Connectivity Section 16: Enabling Internet Connectivity There are three common methods of connecting a small office to the Internet. Internet connections can be wired or wireless. In wired connections, the medium is either copper, which carries electrical signals, or optical fiber, which carries signals in light. For wireless connections, the medium is the atmosphere of the earth, and the signals are carried by radio frequencies. The copper medium includes cables, such as twistedpair telephone wire, coaxial cable, or (most commonly), Category 6 UTP cable. Optical fibers are thin strands of glass or plastic that transmit digital signals by means of modulated pulses of light. Depending on the speed of the connection, and the type of optical fiber, the wavelength of light may be in the visible spectrum or in the infrared (nonvisible) spectrum. CAUTION: Never look into an active optical fiber. Immediate eye damage and permanent blindness can result from viewing a highenergy light source. Use an optical power meter or optical TDR to validate a fiberoptic transmission path. Your eyes can be damaged even if the light is not in a visible wavelength. Wireless Internet carriers offer several different connectivity choices. One option is the home wireless connection between a wireless router and a computer with a wireless network card. Another option is the terrestrial wireless connection between two ground stations. Wireless Internet connectivity can also be achieved through the communication between ground receivers on earth and satellite communication between satellites in geostationary orbit. In a typical journey across the Internet, a packet may pass across diverse media types. Copper medium is used by DSL, cable (DOCSIS), and serial connectivity methods. DSL sends signals across existing telephone lines, while cable Internet services leverage the CATV infrastructure. Serial links use the classic analog and digital local loops. With DSL and cable, the incoming lines are terminated into a modem that converts the incoming digital encoding into Ethernet format. With serial links, the termination is performed by a CSU/DSU. In all three cases, the Ethernet output is sent to a router that is part of the CPE. Due to its immunity to EMI and RFI, fiberoptic cabling is well suited to harsh environments. The fiberoptic cable medium has the added benefit of extending the distance of cable runs far beyond the capabilities of copper cable. The Demarcation Point Although functions within the service provider network are not usually of concern to customers, there are some terms and concepts that you should be familiar with. Service providers install a connection point (usually in the form of an RJ45 jack) that physically connects a circuit to the nearest switching office. This link is known as the demarcation point and it represents the point at which the service provider responsibility is said to end. In other words, the service provider ensures that the link functions correctly up to that point. The other end of this link connects to the service provider network. These links are part of what is known as the local loop, or last mile. The local loop may consist of a variety of technologies, including DSL, cable, fiber optics, traditional twistedpair wiring, and others. The customer side of the demarcation point is the location of the CPE. The term CPE has different meanings, but it traditionally refers to the equipment that is owned and managed by the customer for the purpose of connecting to the service provider network. However, many companies lease CPE from their service providers, and this equipment is still considered to be CPE. Before physically connecting to a service provider network, a company needs to determine the type of WAN service or connectivity that it requires. The exact demarcation point can be different from country to country. The example that is shown in the figure is typical for the United States. Up Next: Dynamic Host Configuration Protocol