nnels enable fiber to reach terabits (1,000 gigabits) of capacity. www.TechnicalPDF.com Coherent fiber optics is one of the technologies that enable high bandwidth transmissions above 40 Gbps. Coherent fiber transmissions achieve high bandwidth by the use of error correction bits in transmitted light pulses, and in lasers located in receivers. At the receiving end, receivers are equipped with lasers tuned to the exact same frequency and shape as the transmitted wavelength. Each wavelength has an associated laser in the receiver in fiber-optic networks that optical network providers build. Receivers use sophisticated algorithms to correct for impairments in the signals sent from lasers associated with each wavelength. Coherent transmission is an important enabler of high bandwidth transmission in long-haul networks because increasing the speed of transmissions causes additional impairments. Long-haul networks are those connecting cities, and countries. Undersea fiber-optic cables that connect continents to each other are also examples of long-haul networks. Half Duplex: Sending and Receiving on Separate Cables Fiber-optic cables are half duplex. Each fiber cable is capable of sending in one direction only. Consequently, a separate fiber strand is needed for sending and a different fiber for transmitting back in the other direction. In other words, each strand of fiber can send signals in one direction only. In contrast, copper cabling is full duplex. Within buildings a single copper cable is connected to each computer and printer. This single cable is used both to send and receive signals. Moreover, cable modems and routers within people's homes require just one copper cable to both send and receive e-mail messages and files to and from the Internet. See Table 1-1 for examples of half VS. full duplex. Table 1-1 Half Duplex VS. Full Duplex www.TechnicalPDF.com Half and Full Type of Cabling for Where Duplex Deployed Separate cables Locations with fiber or copper duplex for sending and cabling receiving Example Fiber