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Chapter 8

# Chapter 8 - Chapter 8 Exercises ‘3 ‘ 8.1-1 If a...

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Unformatted text preview: Chapter 8 Exercises ‘3: ‘. 8.1-1 If a plesiochronous network operates from Cesium beam clock which is accurate to :t 3 parts " in 1012, how long will it take for a D83 signal transmitted between two networks to become out“ " of sync if a 1/4 bit length time error results in desynchronization? Solution: A D83 bit is transmitted in l/(44.736-106) = 2235336108 sec. In the worst case, both network clocks will be out of synchronization by 6 parts in 1012. 2.235336-10’8/(6-10'12) = 3922.27 sec/bit or 980.57 sec/ 1A bit 8.1-2 For the bit stream 011100101001111011001 draw an AMI waveform. Solution: W Note that typically, for illustrative purposes, the waveform is given as W 8.1-3 For the following waveforms, determine if each is a valid AMI format for a D51 signal. If not, explain why not. a. Solution: No. 16 0’5 violation W Solution: No. bi-polar violation c Solution: No. 1’s density violation (1 Solution: Yes v e1“ , r 68 V8.14 a) You have received the following sequence of ESF W bits ...00110010110010110... Is this a' legitimate framing bit sequence in order to maintain synchronization between the T1 transmitter and receiver? Yes No If yes, why? If no, why not? Solution: No. The bit sequence 00]] cannot be in an ESF framing bit sequence. b) The following Tl AMI signal is received: Is this an acceptable Tl signal? Yes No a. If yes, explain. I). If no, explain why not (what, if any, DSl standards are violated) and draw on the ﬁgure the AMI waveform which would be transmitted by the DSU? Solution: No. 16 0’5 violation. The 16 0’5 will be replaced by a pattern of 1’s by the DSU. 8.1-5 The signal 110100000000000000001 is received by the DSU in a T1 data stream which uses a 8825 format. Draw the output of the DSU for this signal? The ﬁrst 1 is already drawn. Show the bit stream which is substituted by the DSU. Solution: 81-6 T-l synchronization at two distant locations is controlled by separate crystal controlled oscillators which differ in frequency by 125 parts per million. If the terminal equipment doesn't maintain sync in how many complete D4 superframes will the faster oscillator have generated (at most) one more time slot (8-bit) than the slower oscillator ? Circle the correct answer. 69 a) 5 b) 10 c) 15 d) 20 e) None of the above - if "none", what is the number of D4 superframes before an extra time slot is generated? Solution: e) The faster oscillator will generate 125- 10'61544- 106 = 193 bits per second more than the slower oscillator. This is one frame/sec = 24.125 time slots. Hence, a time slot difference will be generated in 1/24.125 = 004164498 frames or 00034704 superframes. 8.1-7 Two plesiochronous digital networks, A and B, utilize Cesium beam clocks accurate to 3 parts in 10”. The networks are operated by independent long distance companies and are synchronized to each other by means of a UTC signal. a. If a company leases a T1 line with D4 framing which is terminated at one end in network A and at the other end in network B, how often must the networks be resync’d to each other to avoid a framing bit error in the customers T1 signal in the worst case? {You may assume a framing bit error occurs when the two networks are out of sync by 2 1/2 of a T1 "bit time".} Solution: A T1 bit time is “(1.544106 ) = 6.4766840"7 sec/bit. In the worst case, the two clocks would be off by 2-3 = 6 pans in 1013 or 6- 10'13 errored bits per bit transmitted. Hence, 6.47668. 10'7 sec/bit/ 6-10'13 en‘ored bits per bit = 1.07945-10‘5 seconds per errored bit or 5.39723-106 seconds per errored half-bit. b. UTC operates via GPS satellites which are approximately 23,000 miles above the Earth. How long, in terms of T1 bits, will a correction signal take to be transmitted to the network switches? Solution: The speed of light is approximately 186000 miles/sec. 23000x2 == 46000miles up and down. 46000/ 186000 = 0.247 sec 0.247x1544000 .=. 381850 bits 70 ...
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Chapter 8 - Chapter 8 Exercises ‘3 ‘ 8.1-1 If a...

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