422:
28:
194:. In the T-carrier example, the bipolar signals are regenerated at regular intervals so that signals diminished by distance are not just amplified, but detected and recreated anew. Weakened signals corrupted by noise could cause errors, a mark interpreted as zero, or zero as positive or negative mark. Every single-bit error results in a violation of the bipolar rule. Each such
80:(RZ) is that when a bipolar encoded channel is idle the line is held at a constant "zero" level, and when it is transmitting bits the line is either in a +V or -V state corresponding to the binary bit being transmitted. Thus, the line always returns to the "zero" level to denote optionally a separation of bits or to denote idleness of the line.
177:
The modification of bit 7 causes a change to voice that is undetectable by the human ear, but it is an unacceptable corruption of a data stream. Data channels are required to use some other form of pulse-stuffing, such as always setting bit 8 to '1', in order to maintain a sufficient density of ones.
136:
sequences that don't carry data to the signal. These alternative approaches require either an additional transmission medium for the clock signal or a loss of performance due to overhead, respectively. A bipolar encoding is an often good compromise: runs of ones will not cause a lack of transitions.
181:
If the characteristics of the input data do not follow the pattern that every eighth bit is '1', the coder using alternate mark inversion adds a '1' after seven consecutive zeros to maintain synchronisation. On the decoder side, this extra '1' added by the coder is removed, recreating the correct
254:
like digital audio subsystems for the MAC family, up to 50% of data reduction was possible in both Stereo and Mono transmission modes. At least with some data transmission systems, duobinary can perform lossless data reduction though this has seldom been utilized in practice.
116:, as the positive and negative pulses average to zero volts. Little or no DC-component is considered an advantage because the cable may then be used for longer distances and to carry power for intermediate equipment such as line
140:
However, long sequences of zeroes remain an issue. Long sequences of zero bits result in no transitions and a loss of synchronization. Where frequent transitions are a requirement, a self-clocking encoding such as
132:
whenever signal transitions are required to maintain synchronization between the transmitter and receiver. Other systems must synchronize using some form of out-of-band communication, or add
160:
equipment today, but successful transmission relies on no long runs of zeroes being present. No more than 15 consecutive zeros should ever be sent to ensure synchronization.
250:
to encode the digital audio, teletext, closed captioning and selective access for distribution. Because of the way
Duobinary was coupled to the
295:
216:) ensure regular transitions regardless of the data being carried. In this way, data throughput of 64 kbit/s per channel is achieved.
182:
data. Using this method the data sent between the coder and the decoder is longer than the original data by less than 1% on average.
100:, whereas a binary 1 is encoded alternately as a positive voltage or a negative voltage. The name arose because, in the context of a
316:
17:
372:
198:(BPV) is an indication of a transmission error. (The location of BPV is not necessarily the location of the original error).
212:
For data channels, in order to avoid the need of always setting bit 8 to 1, as described above, other T1 encoding schemes (
566:
174:
T-carrier uses robbed-bit signaling: the least-significant bit of the byte is simply forced to a "1" when necessary.
464:
449:
243:
454:
444:
571:
227:
A very similar encoding scheme, with the logical positions reversed, is also used and is often referred to as
65:, where two nonzero values are used, so that the three values are +, −, and zero. Such a signal is called a
540:
622:
365:
120:. The DC-component can be easily and cheaply removed before the signal reaches the decoding circuitry.
314:"T1 Fundamentals", Revision 1.0, dated 23 January 1997, by Digital Link, retrieved on 25 January 2007
332:"All You Wanted to Know About T1 But Were Afraid to Ask", Bob Wachtel, retrieved on 25 January 2007
34:
number, as represented in bipolar encoding, known as AMI (Alternate mark inversion), where :
612:
342:
288:
617:
350:
628:
358:
153:
133:
89:
634:
607:
510:
164:
163:
There are two popular ways to ensure that no more than 15 consecutive zeros are ever sent:
8:
665:
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520:
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313:
660:
129:
505:
421:
396:
213:
207:
195:
97:
178:
Of course, this lowers the effective data throughput to 56 kbit/s per channel.
535:
104:, a binary '1' is referred to as a "mark", while a binary '0' is called a "space".
530:
459:
320:
299:
191:
602:
545:
525:
515:
439:
411:
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142:
113:
77:
58:
654:
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168:
157:
331:
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70:
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may be more appropriate, though they introduce significant overhead.
146:
101:
62:
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27:
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The use of a bipolar code prevents a significant build-up of
190:
Another benefit of bipolar encoding compared to unipolar is
592:
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224:
is the original line coding type used in Europe and Japan.
221:
217:
96:. In this code, a binary 0 is encoded as zero volts, as in
31:
293:, last updated 28 February 2001, retrieved 25 January 2007
73:, spending equal amounts of time in the + and − states.
152:
The coding was used extensively in first-generation
76:The reason why bipolar encoding is classified as a
652:
69:. Standard bipolar encodings are designed to be
156:networks, and is still commonly seen on older
500:
366:
343:Telecom Dictionary, retrieved 25 January 2007
309:
307:
123:
242:, and essentially all family members of the
201:
325:
220:is a newer format for North America, where
83:
373:
359:
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336:
289:"alternate mark inversion (AMI) signal",
231:. This encoding is otherwise identical.
26:
14:
653:
465:Differential Manchester/biphase (Bi-φ)
445:Non-return-to-zero, level (NRZ/NRZ-L)
354:
450:Non-return-to-zero, inverted (NRZ-I)
246:Television Transmission family used
107:
92:, of which the simplest example is
24:
234:
185:
128:Bipolar encoding is preferable to
88:One kind of bipolar encoding is a
25:
677:
567:Carrier-suppressed return-to-zero
455:Non-return-to-zero, space (NRZ-S)
420:
384:(digital baseband transmission)
244:Multiplexed Analogue Components
145:or some other more complicated
572:Alternate-phase return-to-zero
282:
13:
1:
275:
541:Eight-to-fourteen modulation
7:
258:
10:
682:
623:Pulse-amplitude modulation
291:ATIS Telecom Glossary 2000
205:
124:Synchronization and zeroes
580:
559:
473:
429:
418:
389:
319:January 29, 2007, at the
202:Other T1 encoding schemes
618:Pulse modulation methods
501:Alternate mark inversion
94:alternate mark inversion
84:Alternate mark inversion
18:Alternate mark inversion
613:Ethernet physical layer
229:pseudoternary encoding
53:In telecommunication,
50:
629:Pulse-code modulation
546:Delay/Miller encoding
298:June 9, 2007, at the
134:frame synchronization
90:paired disparity code
30:
635:Serial communication
608:Digital transmission
511:Coded mark inversion
165:robbed-bit signaling
640:Category:Line codes
521:Hybrid ternary code
481:Conditioned diphase
474:Extended line codes
440:Return to zero (RZ)
560:Optical line codes
214:Modified AMI codes
130:non-return-to-zero
51:
648:
647:
506:Modified AMI code
397:Unipolar encoding
208:Modified AMI code
196:bipolar violation
98:unipolar encoding
16:(Redirected from
673:
536:64b/66b encoding
424:
402:Bipolar encoding
375:
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108:Voltage build-up
67:duobinary signal
55:bipolar encoding
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21:
681:
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531:8b/10b encoding
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321:Wayback Machine
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300:Wayback Machine
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235:Historical uses
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192:error detection
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186:Error detection
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603:Digital signal
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526:6b/8b encoding
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516:MLT-3 encoding
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412:Mark and space
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270:Polar encoding
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265:MLT-3 encoding
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206:Main article:
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143:return-to-zero
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78:return to zero
59:return-to-zero
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407:On-off keying
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390:Main articles
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57:is a type of
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169:bit stuffing
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158:multiplexing
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75:
66:
54:
52:
43:
36:
382:Line coding
71:DC-balanced
44:10100111001
666:Line codes
655:Categories
460:Manchester
432:line codes
276:References
661:Encodings
585:See also:
248:Duobinary
147:line code
118:repeaters
102:T-carrier
63:line code
598:Bit rate
588:Baseband
317:Archived
296:Archived
259:See also
551:TC-PAM
430:Basic
631:(PCM)
625:(PAM)
252:NICAM
240:B-MAC
61:(RZ)
593:Baud
496:2B1Q
491:4B5B
486:4B3T
222:HDB3
218:B8ZS
167:and
37:1337
32:1337
154:PCM
657::
306:^
171:.
114:DC
42:=
40:10
374:e
367:t
360:v
47:2
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
