Sol06 - CHAPTER 6 Bandwidth Utilization: Solutions to...

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1 CHAPTER 6 Bandwidth Utilization: Solutions to Review Questions and Exercises Review Questions 1. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. 2. We discussed frequency-division multiplexing ( FDM ), wave-division multiplex- ing ( WDM ), and time-division multiplexing ( TDM ). 3. In multiplexing , the word link refers to the physical path. The word channel refers to the portion of a link that carries a transmission between a given pair of lines. One link can have many (n) channels. 4. FDM and WDM are used to combine analog signals ; the bandwidth is shared. TDM is used to combine digital signals ; the time is shared. 5. To maximize the efficiency of their infrastructure, telephone companies have tradi- tionally multiplexed analog signals from lower-bandwidth lines onto higher-band- width lines. The analog hierarchy uses voice channels (4 KHz), groups (48 KHz), supergroups (240 KHz), master groups (2.4 MHz), and jumbo groups (15.12 MHz). 6. To maximize the efficiency of their infrastructure, telephone companies have tradi- tionally multiplexed digital signals from lower data rate lines onto higher data rate lines. The digital hierarchy uses DS-0 (64 Kbps), DS-1 (1.544 Mbps), DS-2 (6.312 Mbps), DS-3 (44.376 Mbps), and DS-4 (274.176 Mbps). 7. WDM is common for multiplexing optical signals because it allows the multiplex- ing of signals with a very high frequency. 8. In multilevel TDM , some lower-rate lines are combined to make a new line with the same data rate as the other lines. Multiple slot TDM , on the other hand, uses multiple slots for higher data rate lines to make them compatible with the lower data rate line. Pulse stuffing TDM is used when the data rates of some lines are not an integral multiple of other lines.
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Sol06 - CHAPTER 6 Bandwidth Utilization: Solutions to...

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