архив прош.сесий / архив прош.сесий / sinkhr_v_paket_setyakh
.pdf
Quality Level & Traceability
Сравнение уровня качества источника
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PTP |
SSM QL |
G.781 |
ESMC |
Clock |
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Class |
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Option I |
Option II |
Option I |
Option II |
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0001 |
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QL-PRS |
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80 |
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0000 |
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QL-STU |
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82 |
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0010 |
QL-PRC |
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84 |
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0111 |
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QL-ST2 |
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86 |
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0011 |
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88 |
0100 |
QL-SSU-A |
QL-TNC |
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90 |
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0101 |
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92 |
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0110 |
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94 |
1000 |
QL-SSU-B |
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96 |
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1001 |
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98 |
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1101 |
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QL-ST3E |
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100 |
1010 |
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QL-ST3 |
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QL-EEC2 |
102 |
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1011 |
QL-SEC |
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QL-EEC1 |
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104 |
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1100 |
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QL-SMC |
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106 |
1110 |
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QL-PROV |
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108 |
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1111 |
QL-DNU |
QL-DUS |
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110 |
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S1 byte
Bits 5-8 are used for SSM
ESMC PDUs
ESMC PDUs
EEC EEC
IEEE802.3 Slow Protocol
Informational and Event PDUs withTLVs
clockClass
PTPAttribute Value
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Quality Level & Traceability
Определение лучшего источника синхронизации
NE
PRC
NE SSU-A
Какой источник использовать?
+ QL
+ QL |
+ QL |
NE NE
+ QL
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QL-Disabled Mode |
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QL-Enabled Mode |
1. |
Внешние команды |
1. |
Внешние команды |
2. |
Сбой |
2. |
Quality level |
3. |
Local Priority (per interface) |
3. |
Сбой |
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4. |
Local Priority (per interface) |
References:ITU-T G.871 / G.8261 and Telcordia GR-253-CORE
QL… Quality Level
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Регенерация физического сигнала
Распространение частоты
Передача восстановленногосигнала в физическую среду
Например:
Clock stability quantities
‒ E1/T1, 2,048kHz, 2,048kbps/1,544kbps |
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Physical layer |
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Physical Timing Chain |
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timing interface |
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SEC/EEC |
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SEC/EEC |
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SEC/EEC |
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SEC/EEC |
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Packet
master
Reference
Clock
PSN
Packet-based timing Flow
Packet
Slave
Recovered
Clock + ε
G.823/G.824/G.8261/G.8265
© 2012 Cisco and/or its affiliates. All rights reserved. |
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23 |
Точность при передаче частоты
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Исходный сигнал |
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(e.g. 10 MHz signal) |
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Полученный или |
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восстановленный сигнал |
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1ns Phase offset |
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1 second observation period |
Frequency offset = ΔTime / Time |
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= 1 ns / 1 second |
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= 1 x 10-9 = 1 ppb |
Оценка точности частоты основано на длительном измерении среднего фазового сдвига
Other examples:
•50 µs / 1 second = 50 x 10-8 = 0.05 ppb = 50 ppm •1 µs / 100 seconds = 1 x 10-5 = 10 ppb
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Метрики качества частоты (Wander)
Расчеты на основе фазового сдвига
TIE (Time Interval Error)
‒Phase Difference measured in ns
…определяет точность в определенный момент
MTIE (Maximum TIE)
‒Largest Peak-to-Peak TIE for a particular Observation Interval
…определяет точность и стабильность
TDEV (Time Deviation)
‒Route Mean Square of Bandpass filtered TIE (statistical representation of TIE variance)
…оценивает систематические эффекты
Source:http://users.rcn.com/wpacino/jitwtutr/jitwtutr.htm / Reference:ITU-T G.810
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Проверка распространения частоты
Типовой тестовый стенд
Masks per G.823/G.824/G.8261
TIE |
MTIE & TDEV |
Frequency Verification
E |
E |
EEC/SEC |
EEC/SEC |
ANT-20 |
EEC/SEC |
E1 |
EEC/SEC |
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1 |
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PRC/PRS |
1 |
SyncE |
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SyncE |
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SyncE |
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SONET/SDH |
SONET/SDH |
SONET/SDH |
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Часть 2.
Обзор временной синхронизации (Time)
Что такое время?
Time = Phase + Time of Day
*13:38:54.805UTC Mon Apr 2 2012
Time of Day (TOD) Information
(serial interface on the RJ45 connector)
1PPS Pulse Фаза
(analog signal on the DIN connector)
© 2012 Cisco and/or its affiliates. All rights reserved. |
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Форматы Time-of-Day
Множество разных
форматов |
NTP Format |
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‒ NTP |
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‒ Cisco |
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‒ ISO8601 |
Cisco Format |
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‒ NMEA |
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‒ UBX |
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‒ … |
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Распространение времени
Распространение фазы и ToD в пакетной сети
Источник ToD & 1PPS |
Pulse per |
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Second |
Slave
Master
IEEE1588PTP Exchange
Pulse per
Second
00:00:00 ToD messages
00:00:01
00:00:02
time
PhaseOffset
00:00:0
0
ToD messages 00:00:0
1
00:00:02
ВосстановленныеToD & 1PPS
time
See also ITU-T G.8260
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