L9 - Time Division Multiplexing(TDM Used by telephone...

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Time Division Multiplexing (TDM) Used by telephone network after A/D conversion of voice signals. As has been mentioned, standard sampling rate is 8000 samples/second. Quantization is 7 or 8 bits/second. The standard. TDM frame - 1/8000 = 125 microsecond long - contains 24 channels, 8 bits each plus one extra bit to define the starting point. Insert Figure 2-33
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Insert Figure 2-33 For purely data channels, one bit is always reserved for control and one channel is reserved for faster location of frame start. A data channel can’t steal occasional least significant bits. A mixed voice-channel format would have to reduce voice quantization to 7 bits. Raw bit rate is (24 x 8 + 1) x 8000 = 1.544 Megabits/second. Called a T1 carrier The channel data rate is 7 x 8000 = 56 kb/s, which is why much of data communication has had rates related to 56 kb/s.
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Insert Fig. 2-33 The early voice-only frames had 8 bits per sample, but every sixth frame the least significant bit is stolen for control purposes. Bit 1 - dual purpose: 1. define start of frame 2. Identifying which frames have the stolen bit.
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L9 - Time Division Multiplexing(TDM Used by telephone...

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