packet synchronization and oscillators v4

7/30/2019 Packet Synchronization and Oscillators V4

1/31

CONFIDENTIAL INFORMATION

Training Session

Packet BasedSynchronization


2/31


Overview

Drivers for Packet based synchronisation Traditional Vs Packet based synchronisation

PTP and NTP

Related Standards

Oscillator requirements for Packet based synchronisation


3/31


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 aparticular time slot (channel) for sending and receiving information.

Central Office

Tx0

Tx1

Tx31

Time Slot 0

Time Slot1

Time Slot 31

E1 Stream of information

CH31CH1CH0

125s

CH0

125s

125s

125s

SLIC CODEC

SLIC CODEC

CODECSLIC


4/31


TDM World to Packet World

Time Division Vs Statistical Efficient and low cost

No perfect synchronization required

Bursty traffic like email or internet traffic

Higher level flow control like pause frames

XO

DATA DATA

PHY Layer

Layer 2 - 7

PHY Layer

Layer 2 - 7

XO+/-100ppm +/-100ppm


5/31


Mobile Backhaul is most affected

Requirements for Air interface & Backhaul 16ppb for network and 50ppb for air interface E1/T1

connections provided synchronization

turday, 31 August 2013 5

Base Transceiver Station

(BTS)


(BTS)

Base Station Controller

(BSC)

Mobile Switching Centre

(MSC)

To CO

Base Transceiver Station(BTS)


(BTS)

Base Station Controller

(BTS)

Mobile Switching

Centre (MSC)

To CO

(Node B )

(RNC ) (SGSN )(GGSN )

To ISP

2G

3G

4G


6/31


SyncE and Timing over Packets

SyncE Extending traditional Sync to Ethernet Point to point physical layer technology

Transfers frequency

Timing over packet network

Saturday, 31 August 2013 6

PLL

Timing Distribution Using ToP

BITS/SSU

PLL

ZL30106

ZL30106

1GbEPHYZL30106

ZL30106

1GbEPHY

PRS

TimingPackets

+/-100ppm

DataPackets

ZL30106

ZL30106

1GbEPHY

+/-100ppm

ServerToP

Engine

PLL

TimingPackets

TimingPackets

ZL30106

ZL30106

1GbEPHY

SlaveToP

Engine

Synchronous Ethernet

ZL30106

ZL30106

1GbEPHY

BITS/SSU

PRS

Data Data

ZL30106

ZL30106

1GbEPHY

ZL30106

ZL30106

1GbEPHYZL30106

ZL30106

1GbEPHYZL30106

ZL30106

1GbEPHY

SyncEDPLL

SyncEDPLL

SyncEDPLL


7/31CONFIDENTIAL INFORMATION

Packet timing

Precision Time Protocol (IEEE 1588) and Network Time

Protocol (NTP)

Both uses Time Stamps Time encoded in packets when they leave interface

Protocol ensures the flow of time stamps and is standard Algorithm handles and generates clocks and is proprietary

Phase and Time are known Since there is two way transfer, the round trip delay is known


Master

Slave

t1t2

t3

t4

Round Trip Delay =2

)34()12( tttt

Offset =2

)34()12( tttt



Types of PTP Clocks

Grand Master, Boundary Clock, Transparent Clock &Ordinary Clock


GRAND

Ordinary

Clock



Clock Recovery methods

Filtering of significant instances inputs to filter

For Physical clocks

The transitions on the physical line

For Packet clocks

The packet arrival times

The time stamps at the source and destination


1

10

20

6

15

25

t1=4

Sync message containing an

approximation of t1

t2=11

Follow_Up message containing the

precise sending time (t1)

t3=20Delay_Req message

Delay_Resp message containing t4

t4=17

MasterSlave

t2-t1=Delay+Offsett4-t

3=Delay-Offset

Offset=[(t2-t

1)-( t

4-t

3)]/2

Delay=[(t2-t

1)+( t

4-t

3)]/2

In this example

Delay = 2

Offset = 5



What is fundamentally different?

The pdf (Probability Distribution function) Is Stationary in nature (Defined mean and variance) for

physical clocks

Packet based significant events Packet delay variation Notstationary




Selected packets as significant events

Packets with minimal delay Selected for filtering

Networks are required to meet performance conditions 1% of the timing packets sent by the packet master remain in the 150 s fixed cluster range, starting at the

floor delay in every observation window of 200 s.


-4

-3

-2

-1

0

1

2

3

4

0 50 100 150 200 250 300 350 400 450 500Delay

Time

Floor Delay

150 S

200s 200s 200s 200s 200s



Challenges

Packet Clock Recovery Challenges Master Accuracy

Timing Packet Rates

Number of nodes from Master to Slave

Packet Size mix in the network

Queuing techniques in Switches & Routers

Underlying transport mechanism (DSL, Microwave)

Asymmetry of the network (Fibre delays)

Incomplete Standards bodies directions

Many current implementations are on field trials




Standards Activities

PEC Packet Equipment Clock

On Path Support / Aware All intermediate nodesBC/SyncE


Category PEC with Frequency,Phase/Time

(Unaware Networks)

PEC Frequency ONLY

(No On-Path Support /

Unaware Networks)

PEC with Phase/Time

(With On-Path Support / Aware)

Network

Limit

Various network configurations

Implementations with

1. 5 switch, no SyncE

2. 10 switch + 10 SyncE

G.8261 and G.8261.1

(Timing and synchronization

aspects in packet networks

(frequency))

G.8271

(Time and phase synchronization

aspects in packet networks)

Equipment

Limit

No Standards available

Proprietary implementations

G.8263.1 [Master]

G.8263.2 [Slave]

Packet Master and Slave

Performance guidelines

G.8272 [PRTC]

G.8273.1 [Master]

G.8273.2 [BC w/SyncE]

G.8723.2 [BC wo/SyncE]

G.8273.3 [TC]

G.8273.4 [Slave]


14/31


Traditional filtering Vs packet clocks

Traditional Stratum 3 filters are 0.1 Hz to 10z

Time constants are 0.01s to 1.6s

Packet Clocks has narrower filters due to nature ofsignificant events 1mHz to .05mHz or lower!

Time constants are 160 seconds to 54 minutes

This means the PLL control will change the output at alower rate


f2

1

t

F(t)

t

F(t)

54 minutes

63%PLL


15/31


Impact of the Oscillator

Stratum 3 time constant is ~2 seconds The oscillator has not much effect

Packet clocks have time constant of, say, 54 minutes

The oscillator has big effect especially temperature changes

A change of 0.5C/min is about 30C!

F v T performance and Aging directly impacts the packetbased clocks


Phase detector

&

Low Pass Filter

DCO

XO


16/31


Temperature effects of Oscillators


TemperatureSensor

CompensationNetwork or

Computer

XO

Temperature Compensated (TCXO)

-450Cf

f

+1 ppm

-1 ppm

+1000CT

Oven

control

XO

Temperature

Sensor

Oven

Oven Controlled (OCXO)

-450Cf

f+1 x 10-8

-1 x 10-8

+1000CT

Voltage

Tune

Output

Crystal Oscillator (XO)

-450C

-10 ppm

+10 ppm

250C

T

+1000C

f

f


17/31


Oven Control methods


TemperatureLower

Turnover

Point (LTP)

UpperTurnover

Point (UTP)

f (UTP)

f (LTP)

Freq

uency Oven Set Point

-40C 85C

-40C 85C

Oven temperature variation

due to external temperature

change


18/31


PDV filtering with Various Oscillator types


+

Filter

=

Filter

+

Filter

=

Filter

+

Filter

=

Filter

PDV of Network

PDV of Network

PDV of Network

Oscillator Noise - XO

Oscillator Noise - TCXO

Oscillator Noise -OCXO

PLL Output Noise

PLL Output Noise

PLL Output Noise


19/31


Oscillator dependence


Free-run Accuracy The accuracy of an PEC without using an input

reference Oscillator error due to all error sources in the frequency

domain

Wander Generation The amount of wander generated by the PEC when

locked to an ideal reference Oscillator noise measured in the time domain using

MTIE & TDEV metrics

Holdover Stability The stability of an PEC when after losing lock to its

input reference Oscillator drift due to ageing, temperature, voltage and

other effects measured in the frequency domain


20/31


Oscillator noise effect on frequency

The frequency accuracy of the system is directlyimpacted by (Oscillator related)

Temperature variations

Ageing of the oscillator

Loop bandwidth

Eg. An oscillator with temperature stability 100ppb,ageing 10ppb/24 hours.

Assuming the loop bandwidth is small enough not to remove theageing effect, we can approximate a 5 day frequency stability

as: 100ppb + 5 days * 10ppb = 150ppb is the worst case stability

after 5 days



21/31


Stratum Hierarchy

Stratum 3E 12ppb

Stratum 3 370ppb


Pluto

Mercury


22/31


Oscillator impact on Phase

Phase error is accumulation of frequency error


F1

F2

PhaseE

r

ror

t

F1

F2

Constant frequency difference

t

F1

F2

Linear frequency difference

Phase is polynomial

of degree 2


23/31


Impact of Slope Spec on Phase

Slope spec has parabolic effect on Phase


0

5

10

15

20

25

0

10

20

30

40

50

60

70

80

90

100 200 300 400 500 600 700 800 900 10001100120013001400150016001700180019002000210022002300240025002600270028002900

F1

F2

F1 Phase

F2 Phase

Phase and Frequency (F1)

Phase and Frequency (F2) Phase

Error Limit

Time to

reach

limit = 550s

Time to reachlimit = 1550s


24/31


Effect Slope Spec of Oscillator

The OCXO1 is better than OCXO2, because of slope spec


-40 85

OCXO1

OCXO2

Temp window of operation


25/31


Rakon Standards Efforts ITU T

Contribute to ITU with a temperature profile

Oscillator output variations within G.8263 limits To be added as an appendix in the next release

Limited temperature excursions It is proposed therefore that a limit of +/-20C movement at

(0.5C/min or 1C/min as required) be taken to cover both theexternal and internal environmental effects.

Where ts is the test stabilisation time, tL is the time required forthe loop to recover, T is the maximum temperature excursion,T/ t is the ramp rate


tL

tL

tL

tLT

tL

ts T/ t

T


26/31


Mercury G.8263 Compliant*

* When the temperature profile is applied



27/31


Rakon Standards Effortsd

The d parameter

Used to be historically mentioned in standards without mentionof how to measure.

Rakon supported to get rid of this in new G.8263

Enables Mercury to comply with G.8263 holdover requirements



28/31


Rakon Standards Efforts Others

The following contributions are under consideration

Rakon supports the Wander generation specification

to be adjusted for 11ppb including the temperature efforts, fromthe current 10ppb

Gives a bit more room for the loop

Oscillator start up conditions for PDV tolerance testing

Appendix I of G.8263 about PDV tolerance testing methodologymay contain the following text

The recommended oscillator startup considerations may beconsulted before the testing of the PDV tolerance starts.



29/31


Suggested Selection Table


Oscillator Type Rakon OscillatorFamily

Oscillator Parameters

Time to reach phase error

limit with +/-20 temperature

variation @ 10C/hour

Total Phase

movement

Cost

Indicator

Freq v Temp Daily

Ageing

1S 3 S 7 S 24 Hours

(Constant

Temp)

OCXO ROX Stratum 20.1ppb

0.05ppb/day

12

Hours

48 hours 144

Hours


30/31


Summary

Technology change from Circuit Switched to packetswitched networks

Challenges for Synchronization

Methods for Packet Synchronization

Importance of Oscillators on Packet Synchronization



31/31

The End

Thank you

packet synchronization and oscillators v4

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