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| Frage | Antworten |
| It is the transmission of information from one or more sources to one or more destinations over the same medium. | Multiplexing |
| General types of Multiplexing | 1. Time-Division Multiplexing (TDM) 2. Frequency-Division Multiplexing (FDM) 3. Wavelength-Division Multiplexing (WDM) 4. Phase-Division Multiplexing (PDM) 5. Space-Division Multiplexing (SDM) |
| involves the conversion of standard logic levels to a form more suitable for transmission (e.g. digital waveform). | Digital Line Encoding |
| Factors to consider when selecting a line encoding format | 1. Transmission voltages and DC component 2. Duty cycle 3. Bandwidth consideration 4. Clock and framing bit recovery 5. Error detection |
| can be categorized either as unipolar (UP) or bipolar (BP). | Transmission voltages |
| transmission of binary data involves transmission of a single nonzero voltage level. | Unipolar |
| transmission of binary data involves transmission of two nonzero voltage levels. | Bipolar |
| The __________ of a binary pulse can be used to categorize the type of transmission. | duty cycle |
| Two types of duty cycle are ______ and _______ | Nonreturn to Zero (NRZ) and Return to Zero (RZ). |
| In NRZ, a binary pulse is maintained for the entire bit time. | NRZ |
| In ____, active time of the binary pulse is less than 100% of the bit time. | RZ |
| Some line-encoding formats based on the transmission level and duty cycle: | 1. UPNRZ 2. BPNRZ 3. UPRZ 4. BPRZ 5. BPRZ-AMI (Alternate mark inversion) 6. B8ZS 7. B6ZS 8. B3ZS 9. Digital Biphase |
| This condition occurs when a long string of 1s (or 0s) causes the receiver to lose its amplitude reference. | DC Wandering in NRZ |
| This would result to misinterpretation of binary data (i.e. 1s may be interpreted as 0s because of the noise margin). | DC Wandering in NRZ |
| The ____________ required to propagate a line-encoded digital signal is equal to the highest fundamental frequency associated with the signal. | minimum bandwidth |
| is based on the fastest transition in the bit sequence. | Highest fundamental frequency |
| When does the fastest transition occur? • In UPNRZ: ________________ | when alternating 1s and 0s occur |
| When does the fastest transition occur? • In BPNRZ: ______________ | when alternating 1s and 0s occur |
| When does the fastest transition occur? • In UPRZ: ________________ | when successive logic 1s occur |
| When does the fastest transition occur? • In BPRZ: __________________ | when successive logic 1s or success logic 0s occur |
| When does the fastest transition occur? • In BPRZ-AMI: ___________________ | when two or more successive logic 1s occur |
| Highest fundamental frequency for UPNRZ has one cycle for _____ bit times | two or 2 |
| Highest fundamental frequency for BPNRZ has one cycle for ____ bit times. | two or 2 |
| Highest fundamental frequency for UPRZ has one cycle for ___ bit time. | one or 1 |
| Highest fundamental frequency for BPRZ has one cycle for ____ bit time. | one or 1 |
| Highest fundamental frequency for BPRZ-AMI has one cycle for ___ bit times | two or 2 |
| ___________ is easily maintained if there are sufficient transitions in the data waveform. Else, lack of transitions would be inadequate for clock recovery. | Synchronization |
| When does lack of transitions happen? • In UPNRZ: __________________ | long string of 1s or long string of 0s |
| When does lack of transitions happen? • In BPNRZ: _______________ | long string of 1s or long string of 0s |
| When does lack of transitions happen? • In UPRZ: ________________ | long string of 0s only |
| When does lack of transitions happen? • In BPRZ: __________________ | none (best for clock recovery) |
| When does lack of transitions happen? • In BPRZ-AMI: __________________ | long string of 0s only |
| With BPRZ-AMI encoding, an error in any bit causes a/an _____________ (BPV) or the reception of two or more consecutive logic 1s with the same polarity. | bipolar violation |
| This ensures that sufficient transitions occur in the data stream (aka ones density) by substituting a logic 1 when there are several succeeding logic 0s. System must have a mechanism for monitoring the logic values. Typically applied to T1 system. | Binary Eight Zero Substitution (B8ZS) |
| two patterns that are substituted in B8ZS | + - 0 - + 0 0 0 - + 0 + - 0 0 0 |
| Similar to B8ZS, this method ensures that sufficient transitions occur in the data stream when there are successive zeros. Typically applied to T2 system. | Binary Six Zero Substitution (B6ZS) |
| two patterns that are substituted in B6ZS | 0 + - 0 - + 0 - + 0 + - |
| Similar to B8ZS and B6ZS, this method ensures that sufficient transitions occur in the data stream when there are successive zeros. Typically applied to T3 system. | Binary Three Zero Substitution (B3ZS) |
| four patterns that are substituted in B3ZS | 00- -0- 00+ +0+ |
| is sometimes called the Manchester code or diphase. | Digital biphase |
| It is a popular type of line encoding that produces a strong timing component for clock recovery and does not cause DC wandering. It has no built-in error detection mechanism. It has an average DC voltage of 0V assuming an equal probability of 1s and 0s. | Digital biphase |
| Digital biphase represents logic ____ using one square wave cycle at 0° phase | 1 |
| Digital biphase represents logic ____ using one square wave cycle at 180° phase | 0 |
| transmissions from multiple sources occur on the same facilities but not on the same time. | Time-Division Multiplexing (TDM) |
| Transmissions are interleaved in the time domain (using _________). | time slots |
| TDM is predominantly used for ______ signals. | digital |
| A ___________ is a communications system that uses digital pulse rather than analog signals to encode information. | digital carrier system |
| AT&T’s (Bell system’s) ____ Digital Carrier System is recognized as the North American Digital Multiplexing Standard since 1963 and is recognized by ITU-T as Recommendation _______. | T1 ; G.733 |
| In T1 Digital Carrier System, ____ voice-band channels with ideal bandwidth of 4000 Hz are PCM-encoded and multiplexed for transmission over a single metallic wire pair or fiber transmission line. | 24 |
| D-type (digital) channel banks perform these functions in the PCM-TDM system: (a) _______, (b) _________ and (c) __________ of the 24 voice-band channels. | sampling ; encoding ; multiplexing |
| Types of digital channel banks | 1. D1 2. D2 3. D3 4. D4 5. D5 |
| Type/s of digital channel banks that uses TDM frame | D |
| Type/s of digital channel banks that uses superframe (SF) | D2, D3, D4 |
| Type/s of digital channel banks that uses extended superframe (ESF) | D5 |
| This was used by early T1 carrier systems. This utilized companding and u = 10 | D1 Channel Bank |
| In D1, each TDM frame contains ___ channels with one framing bit added at the start of the frame. | 24 |
| Versions of D1 Channel Bank | • 7-bit magnitude-only PCM code • 7-bit sign-magnitude PCM code • 7-bit sign-magnitude PCM code with signaling bit (essentially 8 bits) |
| Line speed , Frame rate, and Channel speed of 7-bit magnitude only PCM codes | 1.352 Mbps ; 8 kbps ; 56 kbps |
| Line speed , Frame rate, and Channel speed of 7-bit sign-magnitude PCM codes | 1.352 Mbps ; 8 kbps ; 56 kbps |
| Line speed , Frame rate, and Channel speed of 7-bit sign-magnitude PCM codes with signaling bit | 1.352 Mbps ; 8 kbps ; 56 kbps |
| In D2 and D3 channel banks, every group of 12 TDM frames is called a _______________. | SF or Superframe |
| Superframe is also known as ___________. | D4 Framing |
| Similar to D1, each TDM frame has 24 channels and the framing bit occurs at the start of every TDM frame. | D2 and D3 Channel Banks |
| However, _________ bits are no longer simply alternating 1s and 0s. | framing |
| Unlike D1, signaling bit was only inserted every ____ frames. | 6 |
| Signaling bit is inserted using ________ signaling. | robbed-bit |
| This widely implemented the superframe format | D4 Channel Bank |
| Unlike predecessors, D4 channel banks time-division multiplexes ___ voice-band telephone channels. | 48 |
| Essentially, SF = ____ TDM frames for D4 channel banks. | 2 |
| A D4 (DS1-C) frame contains _____ bits. | 394 |
| Line speed of UST ECE | engrjbr 2017 D4 Channel Bank | 3.152 Mbps |
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