197:
the frame and is referred to as the "stuffable bit". If it does not contain data (i.e. it's a gap) it is "stuffed". The data from the 4 data streams in now contained in 4 data streams of 2.112 Mbit/s which are synchronous and can easily be multiplexed to give a single stream of 8.448 Mbit/s by taking 1 bit from stream #1, followed by 1 bit from stream #2, then #3, then #4 etc. Some of the fixed gaps accommodate a synchronisation word which allows the demultiplexer to identify the start of each frame and others contain control bits for each stream which say whether or not the stuffable bit is stuffed or not (i.e. contains data or not). The process can then be reversed by the demultiplexer and 4 data streams produced with exactly the same bit rate as previous. The timing irregularity is ironed out using a
205:
to zero) so cannot be entirely eliminated by the filtering effects of the phase lock loop. The worst possible stuffing ratio would be 1 frame in 2 as this gives a theoretical 0.5 bit of jitter so the stuffing ratio is carefully chosen to give theoretical minimum jitter. In a practical system however, the actual decision to stuff or not may be made by comparing the read address and write address of the input buffer store so the position in the frame when the decision is made varies and adds a second variable dependent on the length of the store.
25:
418:
196:
This is slightly greater than 2.048 Mbit/s + 50ppm. If an extra gap is added, this is slightly smaller than 2.048 Mbit/s – 50ppm. Thus on average the data rate can be made exactly equal to the incoming rate by adding a gap in some frames and not others. This extra gap is in a fixed place in
208:
The process is sometimes called "pulse justification" because "justification" in printing is adding gaps so that each line takes up a full column width. It is believed that this term was preferred because "...... stuffing stuffable bits", and "waiting time jitter is the jitter you get while waiting
204:
This scheme does not allow the addition of a stuffed bit as soon as it is required because the stuffable bit is in a fixed point in the frame so it is necessary to wait until the stuffable bit time slot. This wait results in "waiting time jitter" which can be arbitrarily low in frequency (i.e. down
189:
In order to transport multiple data streams from one place to another over a common transmission medium, they are multiplexed in groups of four. Because each of the four data streams is not necessarily running at the same rate, some compensation has to be introduced. Typically the multiplexer takes
176:
PDH allows transmission of data streams that are nominally running at the same rate, but allowing some variation on the speed around a nominal rate. By analogy, any two watches are nominally running at the same rate, clocking up 60 seconds every minute. However, there is no link between watches to
185:
The data rate is controlled by a clock in the equipment generating the data. The rate is allowed to vary by ±50 ppm of 2048 kbit/s (according to ITU-T recommendation). This means that different data streams can (and probably do) run at slightly different rates from one another.
173:(SONET) equipment over the ten years ending around the turn of the millennium (2000), whose floating payloads relaxed the more stringent timing requirements of PDH network technology. The cost in North America was $ 4.5 billion in 1998 alone, p. 171.
422:
190:
the data from the 4 incoming 2.048 Mbit/s data streams and feeds each into a 2.112 Mbit/s stream via a buffer store leaving a series of fixed gaps in each frame.
42:
89:
61:
155:, time, and refers to the fact that PDH networks run in a state where different parts of the network are nearly, but not quite perfectly,
68:
75:
427:
177:
guarantee that they run at exactly the same rate, and it is highly likely that one is running slightly faster than the other.
463:
57:
458:
337:
255:
108:
193:
The data rate is thus 2.112 Mbit/s x (number of bits in a frame – number of gaps)/(number of bits in a frame)
433:
170:
46:
220:
and frame alignment, giving 34 Mbit/s. Four × 34 Mbit/s, gives 140. Four × 140 gives 565.
82:
166:
291:
229:
130:
356:
Cavendish, Dirceu (June 2000). "Evolution of
Optical Transport Technologies: From SONET/SDH to WDM".
296:
286:
273:
may occasionally be interrupted to allow the buffers to be emptied of some or all of their stored
35:
251:
233:
468:
327:
8:
373:
393:"G.703 : Physical/electrical characteristics of hierarchical digital interfaces"
333:
258:
240:
198:
377:
437:
365:
162:
392:
244:
156:
138:
216:
Similar techniques are used to combine four × 8 Mbit/s together, plus
143:
133:
to transport large quantities of data over digital transport equipment such as
452:
266:
236:
217:
209:
to stuff a stuffable bit", though technically correct, does sound like a
134:
369:
305:
301:
24:
210:
270:
269:) departures among the nodal clocks that control transmission.
274:
262:
261:
between nodes, are made large enough to accommodate small
49:. Unsourced material may be challenged and removed.
450:
16:Technology used in telecommunications networks
355:
329:Understanding Telecommunications Networks
254:, installed to accommodate variations in
109:Learn how and when to remove this message
451:
351:
349:
325:
232:, independent clocks are free-running
223:
47:adding citations to reliable sources
18:
390:
346:
13:
58:"Plesiochronous digital hierarchy"
14:
480:
180:
421: This article incorporates
416:
123:plesiochronous digital hierarchy
23:
434:General Services Administration
34:needs additional citations for
409:
384:
319:
171:synchronous optical networking
1:
312:
167:synchronous digital hierarchy
464:Telecommunications standards
358:IEEE Communications Magazine
7:
459:Computer network technology
292:Digital multiplex hierarchy
280:
230:telecommunications networks
165:replaced PDH networks with
163:Backbone transport networks
131:telecommunications networks
10:
485:
129:) is a technology used in
297:List of device bandwidths
287:Bilateral synchronization
429:Federal Standard 1037C
423:public domain material
147:is derived from Greek
326:Valdar, Andy (2006).
151:, meaning near, and
43:improve this article
332:. IET. p. 78.
243:which are used for
224:Independent clocks
141:systems. The term
370:10.1109/35.846090
250:Variable storage
199:phase locked loop
119:
118:
111:
93:
476:
443:
442:
441:
436:. Archived from
420:
419:
413:
407:
406:
404:
403:
388:
382:
381:
353:
344:
343:
323:
114:
107:
103:
100:
94:
92:
51:
27:
19:
484:
483:
479:
478:
477:
475:
474:
473:
449:
448:
447:
446:
426:
417:
415:
414:
410:
401:
399:
389:
385:
354:
347:
340:
324:
320:
315:
283:
245:synchronization
239:located at the
226:
183:
139:microwave radio
115:
104:
98:
95:
52:
50:
40:
28:
17:
12:
11:
5:
482:
472:
471:
466:
461:
445:
444:
440:on 2022-01-22.
408:
383:
364:(6): 164–172.
345:
338:
317:
316:
314:
311:
310:
309:
299:
294:
289:
282:
279:
225:
222:
182:
181:Implementation
179:
144:plesiochronous
117:
116:
99:September 2009
31:
29:
22:
15:
9:
6:
4:
3:
2:
481:
470:
467:
465:
462:
460:
457:
456:
454:
439:
435:
431:
430:
424:
412:
398:
394:
387:
379:
375:
371:
367:
363:
359:
352:
350:
341:
339:9780863413629
335:
331:
330:
322:
318:
307:
303:
300:
298:
295:
293:
290:
288:
285:
284:
278:
276:
272:
268:
264:
260:
257:
253:
248:
246:
242:
238:
235:
231:
221:
219:
214:
212:
206:
202:
200:
194:
191:
187:
178:
174:
172:
168:
164:
160:
158:
154:
150:
146:
145:
140:
136:
132:
128:
124:
113:
110:
102:
91:
88:
84:
81:
77:
74:
70:
67:
63:
60: –
59:
55:
54:Find sources:
48:
44:
38:
37:
32:This article
30:
26:
21:
20:
469:Multiplexing
438:the original
428:
411:
400:. Retrieved
396:
386:
361:
357:
328:
321:
256:transmission
249:
227:
218:bit stuffing
215:
207:
203:
195:
192:
188:
184:
175:
161:
157:synchronized
152:
148:
142:
126:
122:
120:
105:
96:
86:
79:
72:
65:
53:
41:Please help
36:verification
33:
397:www.itu.int
135:fibre optic
453:Categories
402:2016-03-06
313:References
69:newspapers
391:tsbmail.
306:E-carrier
302:T-carrier
234:precision
169:(SDH) or
378:14395608
281:See also
211:pleonasm
308:systems
271:Traffic
252:buffers
153:chronos
149:plēsios
83:scholar
376:
336:
237:clocks
85:
78:
71:
64:
56:
425:from
374:S2CID
267:phase
259:delay
241:nodes
90:JSTOR
76:books
334:ISBN
304:and
275:data
263:time
137:and
121:The
62:news
366:doi
228:In
127:PDH
45:by
455::
432:.
395:.
372:.
362:38
360:.
348:^
277:.
247:.
213:!
201:.
159:.
405:.
380:.
368::
342:.
265:(
125:(
112:)
106:(
101:)
97:(
87:·
80:·
73:·
66:·
39:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
