networks evolution and traditional synchronization
TRANSCRIPT
CONFIDENTIAL INFORMATION
Networks Evolution andTraditional
Synchronization
CONFIDENTIAL INFORMATION
Agenda
› Network Evolution• Networks and Systems
› Need for Synchronization• Standards and networks
› Oscillators• Key in standardized synchronization
CONFIDENTIAL INFORMATION
Access
Access
Equipment
Phone
Last Mile
The Network
DSLAM
DSLModem
BSC
BTS
OLT
ONU
DLC RT
PBX
Phone
CMTS
CableModem
PSN
CO
PSTN
Core
Edge
MSPP
CONFIDENTIAL INFORMATION
Traditional Networks
CONFIDENTIAL INFORMATION
Traditional Telephone networks
Subscriber:Private
Residence
Subscriber:Private
Residence
(Central Office /Telephone exchange)
4-6 Kms of telephone lines from CO to the subscriber
To other COs
To other COs
Last Mile / First Mile / Subscriber Loop / Local Loop
CONFIDENTIAL INFORMATION
Digital Loop Carrier
Subscriber:Private
Residence
Subscriber:Private
Residence
(Central Office /Telephone exchange)
To other COs
To other COs
RemoteTerminal
Last Mile Access Network
PBXCentral Office Terminal
Time Division Multiplexed Channel
CONFIDENTIAL INFORMATION
Time Division Multiplexing
• Time Slot (Channel) : for an established conversation, 8 bits of information (voice sample) are transmitted during a specific time slot.
• To maintain voice quality, voice samples HAVE to be transmitted every 125s, regardless of the number of channels in the stream
In order to assign more than one subscriber to one or two pairs of cable wire, each subscriber is allocated a particular time slot (channel) for sending and receiving information.
Central OfficeTx0
Tx1
Tx31
Time Slot 0
Time Slot 1
Time Slot 31
E1 Stream of information
CH31CH1CH0
125s
CH0
125s
125s
125s
SLIC CODEC
SLIC CODEC
CODECSLIC
CONFIDENTIAL INFORMATION
Pleseochonous Digital Hierarchy
› Plesechronous =Almost the same
› Effect : “Slips” One voice sample lost in many minutes• Acceptable for voice conversation
A B
˜ ˜2.048M +/-50ppm Oscillators
CONFIDENTIAL INFORMATION
PDH Hierarchy
E3/T3/J3
E2/T2/J2
E1/T1/J1
E3/T3/J3
E2/T2/J2
E1/T1/J1
E4/T4/J4
ITU-T Hierarchy
North
American Hierarchy
Signal Designation
Nominal Rate
(Mb/s)
Signal Designation
Nominal Rate
(Mb/s)
E1 2.048 DS1 (T1) 1.544
E2 = 4XE1 8.448 DS2 = 4XT1 6.312
E3 = 4XE2 34.368 DS3 = 7XT2 44.736
E4 = 4XE3 139.264 DS4 = 6 XT3 274.176
CONFIDENTIAL INFORMATION
Voice conversation• Causes a “POP” in the receiver• Must be appreciable rate to interfere with conversation.• Compressed voice will experience more distortion
Digital Data• Retransmission• Compressed Video especially susceptible because only parts of frames are transmitted• Encrypted transmissions must be re-keyed. Not just military, consider e-commerce.
Analog Modems• Fax transmission found that a single slip caused up to eight horizontal scan lines • Can take up to 6 seconds to recover from a phase slip.• Can lose 0.08 inches of data on a fax.
Digital Video • Segments of the picture to be distorted or to freeze • Periods of up to 6 seconds • Length of the distortion depends on the encoding and compression
Slips affect “some” traffic
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Synchronous Digital Hierarchy
› All Network elements are synchronous
› On Average, keep the frequency constant across nodes• With limits on clock phase movement
˜ ˜
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Synchronous Interface
› Synchronization PLL has tough job• To keep up the average frequency• To remove the variations on the line
CDR
Circular buffer
PLL
Received line dataWrite Data
Write Clock
Read Data
Read Clock
System Clock
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Basics of PLLs
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Equivalent Model
› XO presents an HPF
› As the BW becomes narrower, XO effects reflects more at the output
Phase detector & Low Pass Filter DCO
XO
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Hierarchy of clocks
› ITU-T recommendations • G.811
– This Recommendation outlines minimum requirements for timing devices used as primary reference clocks in synchronization networks
• G.812 – Timing requirements of slave clocks suitable for
use as node clocks in synchronization networks
• G.813– Timing characteristics of SDH equipment slave
clocks (SEC)
• G.8262– Timing characteristics of Ethernet equipment
slave clocks (EEC)
• G.783– Characteristics of synchronous digital hierarchy
(SDH) equipment functional blocks
(North America - Telcordia/Bellcore GR-253-CORE, GR-1244-CORE, ANSI T1.101)
I
II II
III III III III
ITU-T G.811
ETSI 300 011Customer PremisesEquipment
ITU-T G.812
ITU-T G.813
Stratum 1
Stratum 4/ 4E
Stratum 3/3E
Stratum 2
CONFIDENTIAL INFORMATION
Clock Performance Levels
No RequirementNo32 ppmN/A+/- 32 ppm
4E
MTIE < 1000nsPhase slope 61us/s
No32 ppmN/A+/- 32 ppm
4
MTIE < 1000ns Objective mask 150nsPhase slope 885ns/s
0.1Hz20 ppm+/- 4.6x10-6 /day+/- 20 ppm
SMC
MTIE < 1000nsPhase slope 61us/s
Objective: MTIE < 150nPhase slope 885ns/s
3Hz0.1Hz (SONET)
4.6 ppm+/- 3.7x10-7 /day+/- 4.6 ppm
3
MTIE < 150nsPhase slope 885ns/s
0.001Hz4.6 ppm+/- 1.2x10-8 /day+/- 4.6 ppm
3E
MTIE < 150ns0.001Hz0.016 ppm+/- 1x10-10 /day+/- 0.016 ppm
2
N/AN/AN/AN/A+/- 1x10-11
1
Phase Transient(Re-arrangement)
Wander Filtering
Pull-in/ Hold-in range
Holdover Stability
Free-run Accuracy
Stratum Level
CONFIDENTIAL INFORMATION
Network Vs Equipment Limits
› Standards are generally classified into two types
› Network Limits – with reference to a PRC• ITU-T G.823 (E1), G.824 (T1), G.825 (SDH), G.8251 (OTN), • ITU-T G.8261 (SyncE, PSC-A, CES, PEC Frequency) • ANSI T1.403, T1.101, T1.105 (SONET)
› Equipment Limits – Input to output of an Equipment • ITU-T G.811 (PRC), G.812, G.813 (SONET/SDH), G.8262
(SyncE) • ITU-T G.8263 (PEC Slave Frequency) • ANSI T1.101, T1.105 • Telcordia GR-1244-CORE, GR-253-CORE
CONFIDENTIAL INFORMATION
Timing Standards Hierarchy
Monday, 17 April 202318
CPE
Access
Metro
Edge
Core
Network TopologyG.811 / PRC/ Stratum 1/ GR-2380 COREGenerated through Atomic Clocks, distributed throughGPS, GNSS or Loran – C Systems
G.812 / SSU / BITS/ Stratum 2 / GR 378 COREGenerated through Rubidium or similar clocks, starts to include holdover Capability, capacity to retain clocks within defined quality even when reference To PRC is lost
G.813 / SMC/ GR-256 CORE/ G.8262PLL implementations controlled through OCXO or VCXO oscillators which cleansUp the clock from upstream and also provides special functions such as holdover
Stratum 3E / GR-1244 COREPLL implementations through OCXO or ICOCXO implementations
Stratum 3Close to the SMC definition, the loop filter bandwidth is relaxed
Stratum 4 and 4ENo holdover requirements, no strict loop filter requirements
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Overview of Timing flow
CPE
Access
Metro
Edge
Core
ATAs, VoIP Terminals, Set top Boxes, DSL Modems, ONTs, Video Confs, Ethernet switches , Small Cells Etc. Traditionally Free run timing. Most of these Systems are moving in to synchronized line timing
PBXs, remote DLCs, ONUs, MTUs, MDUs, DSLAMs, Enterprise Routers, Switches and so on. Traditionally Stratum 4 or 4E timing requirements.
Metro Routers, CMTS Boxes, Routers, Ethernet Switches, OLTs, SDH Add Drop Multiplexers, Muti Service transport platforms etc. Mix of Stratum 4E, SMC, Stratum 3, G.813 timing requirements
Class 5 switches, SDH cross connects, Distribution Routers, Muti Service Provisioning Platforms, OTN Transponders etc. A mix of Stratum 3E, G.813 and G.812 timing
OTN Muxponders, SDH and SONET multiplexers and cross-connects, DWDM and CWDM transponders, Mutiservice Transport platforms, Microwave transport etc. G.812, Stratum2, Stratum 3E, G.813 and Occasionally line timing devices.
Network Topology Applications and Timing requirements
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Wired Technology
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CPE
Access
Metro
Edge
Core
Network Topology
DSL, FTTx, Ethernet & SyncE, VoIP, Fiber Channel, DOCSIS, DECT, WLANZigBee BLUETOOTH, NFC, PCIe , PTP, NTP, Fixed Mobile Convergence, USB, HDMI, HomePlug
DSL, FTTx, Ethernet & SyncE, XAUI, PTP, Fibre Channel, SAN
SONET, SDH, GbE, 10GbE, SynceE, PTP, XAUI
OTN, SONET, SDH, DWDM, 10GbE, 40G, SyncE, PTP
OTN, SONET, SDH, DWDM, 10GbE, 40G, 100G, SyncE, PTP
Associated Technologies
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Wireless Technology
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CPE
Access
Metro
Edge
Core
Network Topology
Base station (node-B) or equivalent box in the mobile network needs to have Network timing usually at 16ppb accuracy (3GPP requirement) andVarious air interface requirements based on the air interface technology Used. The timing is usually Stratum 3E or higher levels, depending on howLong the system needs to remain in active service before the synchronization degrades, forcing the service to shutdown
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Synchronizer Features
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Special Features
• PLL Characteristics
o Free run
o Capture / Lock Ranges
o Jitter / Wander
• PLL Special features
o Holdover
o Phase slopes
o Reference Switching
o MTIE
o Clock Monitoring
CONFIDENTIAL INFORMATION
Time
Stable butnot accurate
0
f
TimeAccurate (on the average) but not stable
f
Time
Not stable andnot accurate
f
Time
Stable andaccurate
f
Accuracy & Stability
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Significance of accuracy and stability
› Accuracy – How close as to a standard reference • Oscillators specify life time accuracy, say 20 years. – Say
+/-4.6ppm• This is the “freerun” frequency out of a system when an
oscillator is let to run by itselfEach oscillator of the above defined family can have output
frequency anywhere between +4.6ppm to -4.6ppm
› Stability – Once locked to a reference or when remember the last locked frequency (holdover) how best it can hold-on to the frequency value• This is a combination of temperature vs frequency
performance and aging
› Stability is the key performer for an oscillator in a synchronization system
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Why Stability is key?
› Variation outside of the loop bandwidth reflects on the output• Eg.
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IdealSignal
RealSignal
Ideal Signal+ Jitter
+
Noise
P-PJitter
Jitterfrequency
Jitter
Jitter <10Hz is called Wander
CONFIDENTIAL INFORMATION
*Jitter frequency (Hz)f = 1/Tj
Jittered Signal
Jitter Amplitude (UI )p-p
1UI p-p
0.3UI p-p
T Jitter Period (sec)Jitter <10Hz = Wander
Jitter & Wander
CONFIDENTIAL INFORMATION
Holdover
› Holdover is ability to remember last known good clock› Holdover Stability is maximum rate of change of the clock
frequency with respect to time upon loss of all frequency references
› Stratum 3 and 3E clocks have 3 components• Initial: the frequency offset immediately after losing all references• Temperature: the total frequency change over a specific temperature
spectrum• Drift: frequency offset applicable to all non-temperature affects such
as aging and other system related (power supply and so on ) changes. On a per day basis.
Component Stratum 3
Initial Offset 50 x 10-9
Temperature 280 x 10-9
Drift 40 x 10-9
Stratum 3E
1 x 10-9
10 x 10-9
1 x 10-9
SMC (GR-253)
50 x 10-9
4100 x 10-9
500 x 10-9
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TIE – Time Interval Error
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MTIE – Maximum Time Interval Error
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TDEV – Time Deviation
› Represents the spectral content of TIE
› Represent the type of noise present in TIE• Flcker, Random etc
› Reveals the loop bandwidth in a PLL application• In general
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Control and Master timing Cards
(Jitter & Wander filtering, Tolerance, Holdover,
Reference Switching Etc)
Timing flow in a transport box
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Uplink (Back Haul) Line card
Line Card PLLLine recovered Clock
Control and Master timing Cards
(Jitter & Wander filtering, Tolerance, Holdover,
Reference Switching Etc)
Service Line cards (Down Stream)
Line Card PLL Transmit Clock
Transceiver
Transceiver
External Timing Signals (BITS etc)
Uplink (Back Haul) Line card Line
Card PLLLine recovered ClockTransc
eiver
Backplane Clocks
Service Line cards (Down Stream)
Line Card PLL
Transceiver
Transmit Clock
Transmit Clock
Transmit Clock
CONFIDENTIAL INFORMATION
Clock Card Vs Line Card PLLs
› Clock Cards• Standards compliance
implementations (SETS)• Jitter/wander filtering• Very good Holdover• Reference switching • Master – Slave capability• Reference monitoring• Multiple inputs rates• Multiple inputs levels• Input jitter/wander
tolerance• Digital Implementations
– medium jitter levels are acceptable
Line cards– Ultra low jitter
– High frequency conversion
– 19M/38M/77M/155M/622M
– reference switching
– Low cost oscillator
– Low holdover accuracy
– Automatic source fail detection
– Automatic switching
– Wider loop bandwidth – Fast locking
– Mixed implementations – Holdover and reference switching Digital and Low jitter frequency multiplication Analog
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Summary
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