Networks Evolution and Traditional Synchronization

CONFIDENTIAL INFORMATION

Networks Evolution andTraditional

Synchronization


Agenda

› Network Evolution• Networks and Systems

› Need for Synchronization• Standards and networks

› Oscillators• Key in standardized synchronization


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


Traditional Networks


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


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


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


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


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


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


Synchronous Digital Hierarchy

› All Network elements are synchronous

› On Average, keep the frequency constant across nodes• With limits on clock phase movement

˜ ˜


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


Basics of PLLs


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


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


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


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


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


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


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


Wireless Technology

Monday, 17 April 202321Monday, 17 April 2023

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


Synchronizer Features


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


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


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


Why Stability is key?

› Variation outside of the loop bandwidth reflects on the output• Eg.


IdealSignal

RealSignal

Ideal Signal+ Jitter

+

Noise

P-PJitter

Jitterfrequency

Jitter

Jitter <10Hz is called Wander


*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


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


TIE – Time Interval Error


MTIE – Maximum Time Interval Error


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


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


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


Summary

Networks Evolution and Traditional Synchronization

Documents

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