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Signal bandwidth1/30/2024 This results in a lower errorrate than an analog signal because the latter uses amplifiers, which increasethe signal as well as any prior distortion to the signal. The primaryadvantage of digital signaling is the ability to regenerate pulses, which meansthat new pulses can replace ones with distortion. The advantages gained by sending the signals as binary data,however, more than offset the requirement for greater bandwidth. Transmission of thesesame 24 voice channels in digital form using the standard T1 time divisionmultiplexing format requires about 776KHz, or about eight times as muchbandwidth (776/96). For example, the transmission of 24analog voice channels requires about 96KHz (24 x 4KHz). Transmission of signals in binary form can require considerably morebandwidth than an equivalent analog signal. Both V.90 and V.92 modems are discussed inChapter 5, "Synchronous Modems, Digital Transmission, and ServiceUnits." Digital Signals A more recent modemreferred to as a V.92 modem permits data transmission up to approximately44000bps in the uplink direction. This new modem is referred to as a V.90 modem. In addition, the 56Kbps data rate isunidirectional, with the maximum modem rate being 33600bps in the oppositedirection. However, the use of this modem at that operatingrate requires one end of the link to be directly connected to the communicationscarrier's digital network. A relatively new type of modem thatpermits only one analog-to-digital conversion is capable of supporting anoperating rate of 56000bps. Throughsophisticated signal-processing techniques, modems can even carry up to 33600bpsusing an analog signal over a voice channel. Modern modems operating at orabove 9600bps use a sophisticated echo-canceling technique that enables bothtransmit and receive signals to flow on a common wire pair. Therefore, four times as much information can besent in the same channel in a given time period. The 1200bps modems also are full-duplex and use mostof the available bandwidth. Thus, the total 600Hz used out of the 3000Hz availablebandwidth is inefficient. The 300bps full-duplex modem signals use two bands of frequencies, eachoccupying about 300Hz. Large-scale integratedcircuits made possible the remarkable increases in performance and decreases inprice of these modems. A good example is the introduction of low-cost modems operating at1440bps for personal computers, which are 48 and 96 times faster thanthe rate of 300bps that was used for a long time. Transmission rates for data communications seem to follow a corollary ofParkinson's Lawthat is, data rates increase to fill the bandwidthavailable. The ratio at which information can be transmitted depends on the bandwidth ofthe transmission media. Learn More Buy Bandwidth Requirements for Signals Understanding Data Communications, 7th Edition
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