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Time Distribution using IEEE 1588 v2 (PTP)

Oscilloquartz SA

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ASZINKRON ÀTVITELI HÀLÒZATOK

SZINKRONIZÀCIÒS KÉRDÉSEI NAPJAINKBAN

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Network synchronization

Node A

Node B

Node C

Node D

Reference

Clock

Distribution of frequency, phase and/or time

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Frequency synchronization

Node A

t

t

Clock signal of node A

Clock signal of node B

Node B

TA = 1 / fA

TB = 1 / fB

fA = fB

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Az idö mértékegysége

Általános Súly- és Mértékügyi Konferencia

(Conférence Générale des Poids et Mesures – CGPM)

1967-ben hozott döntése értelmében

A másodperc az alapállapotú cézium-133 atom két hiperfinom

energiaszintje közötti átmenetnek megfelelő sugárzás

9 192 631 770 periódusának időtartama.

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Frequency source: atomic Cesium clock (Cs)

Example: OSA 3230B cs Clock

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Frequency source: atomic Cesium clock (Cs)

Magnetic Cesium Beam Tube

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Phase synchronization

Node A

t

t

Clock signal of node A

Clock signal of node B

Node B

! ! !

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Time synchronization (time-of-day)

Node A

t

t

Time signal of node A

Time signal of node B

Node B

14/01/00

08:34:56

14/01/00

08:34:57

14/01/00

08:34:55

14/01/00

08:34:55

14/01/00

08:34:56

14/01/00

08:34:57

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Time source: Global Navigation Satellite System (GNSS)

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Performance level: frequency

1 · 10 - 7

1 · 10 - 8

1 · 10 – 9

(1 ppb)

1 · 10 - 10

1 · 10 - 11

1 · 10 - 12

1 · 10 – 6

(1 ppm)

SDH, PSTN, MSC, MGW, BSC, RNC

Radio interface of BTS, Node B, eNode B

Femto Cell

Input of BTS, Node B, eNode B

Fractional (relative)

frequency accuracy [1]

LTE eNode B with Network MIMO

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Performance level: phase & time

1 ms

100 μs

10 μs

100 ns

10 ns

10 ms

LTE with Location Based Service

Power Distribution: Synchro-phasor

IT Time-of-Day distribution

Phase or time

accuracy

1 μs

cdma2000

UMTS-TDD, LTE

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Network Convergence

PSTN

(TDM)

PDCN

(Packet

Switched)

NGN (Packet

Switched)

CONVERGENCE

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Time Distribution via the

Precision Time Protocol PTP (IEEE 1588 v2)

ETHERNET

Base Station Controller

PTP GRAND MASTER CLOCK

Base Station

Base Station

Base Station

Base Station

PTP SLAVE CLOCK

PTP SLAVE CLOCK

PTP SLAVE CLOCK

PTP SLAVE CLOCK

GPS Antenna

Oscilloquartz PTP IEEE 1588 v2 Equipment

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PTP PRINCIPLES

Chapter 1

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SWITCH/

ROUTER

Typical Backhaul Network

RNC/BSC

GRANDMASTER

GRANDMASTER

SWITCH/

ROUTER

METRO TRANS.

NETWORK

AGGREGATION

NETWORK

SWITCH/

ROUTER BTS/NodeB

SLAVE

Phase : 1us

Frequency : 50ppb /16ppb

Primary

Secondary

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IEEE standards

● IEEE 1588 (Precision Time Protocol) is standardized since 2002

● Version 1 of the protocol is used for applications in:

● Industries (e.g. Automation)

● Test and measurement

● Power networks

● Military and Avionic

● Version 2 is released since June 2008 and is made for applications in:

● Telecom

● Broadcasting

● Power and Utilities

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What’s new in PTP v2 ?

● PTPv2 meets accuracy for telecom applications

● High refresh rates up to 64 or 128 messages per second

● Correction field for asymmetric measurements

● Multicast and Unicast or Mixed are available

● Manual and Automatic Master Clock selection methods

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ITU-T standards

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Fact Sheet PTP v2

● PTP (Precise Time Protocol) is an IEEE standard:

● IEEE 1588 v1: for LAN applications

● IEEE 1588 v2: broader application space, incl. telecom

● Protocol for sub-microsecond synchronization of real-time clocks over frame and packet switched networks

● Uses ‘Two-way Time Transfer’ (TWTT) and ‘Hardware Assistance’

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Fact Sheet PTP v2

● The main idea is to mitigate the protocol stack delay with appropriate electronic hardware and a modified TWTT protocol.

● A hardware « Precision Time Stamp Generator » measures the frame receive and transmit times at or close to the Physical Layer (Layer 1).

● The measured frame transmit times are communicated to the other end system with a second message.

● The TWTT calculation expoits the time values measured by the Precise Time Stamp Generator.

● The configuration of the clock hierarchy can be done manually or automaticaly using the Best Master Clock (BMC) algorithm.

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PTP Clock

PTP Entity

e.g. Network Layer

e.g. Data Layer

Physical Layer

Precise Time Stamp

Generator

Physical Network Media

e.g. Tranport Layer

Low

er

Layers

of P

roto

col S

tack

EventPortGeneralPort

Local Clock

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Elements of a PTP System

● Nodes

● Ordinary clocks:

● Communicate with other clocks over a single communication path

● Boundary clocks (optional):

● Communicate with multiple sets of clocks using distinct communication paths

● Administrative nodes (optional):

● For management purposes

● Communication paths

● Network segments that allow direct communication between clocks

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Master Clocks

● The Primary Reference source of time of the network

● Typically synchronized to GPS

● Very stable and accurate

● High-speed PTP time stamp processor

● Min 100 Base-T line speed

Grand Master

Clock

GMC

UTC Reference

LAN/WAN Packet

Switched Network

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Slave Clocks

● Are slaves to the path containing the best clock they can see

● Reduce Jittter and Latencies of packet transit introduced by Network switches and router

● Give time, phase and frequency to the Network Element

Slave Clock SC

LAN/WAN

NE Network

Element

Packet Switched Network

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The Simplest PTP Network

GMC SC

NE

MASTER SLAVE

GPS

Satellite

Network

Element

requiring sync

Packet Switched Network

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Boundary Clocks

● Are slaves to the path containing the best clock they can see

● Are masters to the clocks on all other paths

● Serve to implement time distribution trees

● Are required…

● …in gateways between different communication technologies

● …in network element which block PTP messages

● Are recommended in network elements which insert significant delay fluctuations

Boundary Clock BC

Packet Switched Network

Packet Switched Network

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L1

L2

L3

L4

L5SYNCH

Precise Time

Stamp Generator

e.g. Ethernet Switch or IP Router

Precise Time

Stamp Generator

L1

L2

L3

L4

L5SYNCH

Boundary Clocks Principle

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PTP Network Principle with Boundary Clock

SC

NE

GMC

BC

SC

NE

MASTER

SLAVE MASTER

SLAVE

Packet Switched Network

Packet Switched Network

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● Are typically contained in switching equipment

● Measure the time elapsed between Switch input and Switch output

● Are recommended in network elements which insert significant delay fluctuations

● Not recommended by ITU-T

End-to-end Transparent Clocks

Transparent

Clock

TC

Switch

Packet Switched Network

Packet Switched Network

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Transparent Clock

L1

L2

L3

L4

L5SYNCH

Residence Time

Measurement

e.g. Ethernet Switch or IP Router

L1

L2

L3

L4

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● Are typically contained in switching equipment

● Measure the time elapsed between Switch input and Switch output

● Measure time elapsed between two Transparent clocks

● Are recommended in network elements which insert significant delay fluctuations

● Not recommended by ITU-T

Peer-to-peer Transparent Clocks

Transparent

Clock TC

Switch

TC Transparent

Clock

Switch

Packet Switched Network

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PTP COMMUNICATION

Chapter 2

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Time Exchange between Master and Slave

L1

L2

L3

L4

L5

Packet Switched Network

PTP Slave side PTP Grandmaster side

Frequency, Phase and/or Time-of -day Reference

DATA + SYNC

Time Stamp

SYNC

L1

L2

L3

L4

L5

Time Stamp

SYNC

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Two-Way Time Transfer (TWTT)

TIME

GMC SC

TIME

12:00 12:05

12:01 12:06

12:02 12:07

12:03 12:08

12:05 12:05

T1

T2

T3

T4

(T2-T1) – (T4-T3)

2 = 5 =

(12:06-12:00) – (12:03-12:07)

2

6 – -4

2 =

T Final

T Offset =

Mean Propagation Delay = TSC – T Offset = 12:10 – 5 = 12:05

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PTP V2 Messages

● Announce:

● Entity the Master Clock

● Conveys clock propeties

● Typically sent every 2 sec.

● Sync messages:

● Conveys Master Clock’s time information (T1)

● Follow_up:

● Conveys Master Clock’s time information (T1) in 2-step mode

● Delay_Req messages:

● Used to measure and correct transmission delay

● Conveys estimate of transmit time

● Delay_Resp messages:

● In response to a Delay_Req message

● Used to measure and correct transmission delay

● Conveys precise time stamp of Delay_Req message’s receive time

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Master Selection Methods

● Manual:

● Configured via management system; static.

● Semi-automatic:

● Acceptable master table:

● Configure slave ports to accept only clocks from the table as masters

● Fully automatic:

● Best Master Clock Algorithm (BMCA)

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Best Master Clock Selection

GMC

LAN/WAN

GMC

GMC

SC GMC

GMC

Communication between GMC

GMC Selection

Loss of GMC

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Acceptable Master Table - Redundancy

Master Clock Site

PTP

Grandmaster

GPS

Master Clock Site

GPS

Slave Clock Site

PTP

Slave

Slave Clock Site Slave Clock Site Slave Clock Site Slave Clock Site Slave Clock Site

PTP

Slave

PTP

Slave

PTP

Slave

PTP

Slave

PTP

Slave

PTP

Grandmaster

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PTP PERFORMANCE

Chapter 3

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Definition: Packet Delay δAB(k)

Packet switched

network

End

system

End

system

A B

1 2 k

t

1 2 k

t

Packets/frames received over interface B

Packets/frames sent over interface A

δAB(k)

Consider two interfaces A and B, which are traversed by a given packet flow.

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TWTT (Two-Way Time Transfer ) is not perfect…

● Because of a packet delay asymmetry, the formula is affected by errors.

● In a packet network, the queuing part of the total packet delay is highly asymmetrical, except when there are very low traffic loads.

TIM

E

GMC SC

TIM

E

12:00 12:05

12:01 12:06

12:02 12:07

12:03 12:09

12:05 12:05

T1

T2

T3

T4

T Final

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Factors impacting performance

● Objective: ITU-T G.823 Network Limit for PDH synchronization interfaces

● Performance is impacted by …

● Packet Delay Variation (PDV)

● Packet Delay Asymmetry (PDA)

● PDV and PDA depend on …

● the number of switching / routing nodes

● the traffic load

● QoS mechanisms

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Definition: PDV (Packet Delay Variation) VAB(k)

0

0.1

0.2

0.3

0.4

0.5

0 200 400 600 800 1000k

DA

B(k

) [s

]

DMIN

VAB(k)

NODE NODE NODE A B

VδAB(k)

VδBA(k)

v.1.2 11/10/12 ∙ BIGR slide № 46

Overview of Stand-Alone Products

● Compact 1U / 19’’ rack-mountable units

● PTP Grandmasters

● OSA 5331 PTP Grandmaster – High Performance

● PTP Slaves

● OSA 5320 PTP Slave – Telecom

● OSA 5320 PTP Slave – Broadcasting

● OSA 5320 PTP Slave – Power & Utilities

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OSA 5331 PTP Grandmaster Front Panel

5-BUTTON PAD LCD DISPLAY FRONT LEDs

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OSA 5331 PTP Grandmaster - Rear Panel

Power supply B

Alarm Relay

E1 / 2.048 MHz / T1 / 75 ohms output

E1 / 2.048 MHz / T1 / 75 ohms output

10 MHz 50 ohms output

1PPS Output

Local

Mgmt

Remote

Mgmt

PPS Input

10 / 2.048 MHz Input

DC Power A

GPS input

ToD Output (NMEA 0183) ToD Input (NMEA 0183)

E1 / T1 / 75 ohms input

FE/GbE PTP Port

SFP PTP Port

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TCC-PTP FOR OSA 5548C

Plug-in card

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TCC-PTP (Time Code Card – PTP)

● Plug-in card for the OSA 5548C SSU/TSG

● Enhances PTP v2 Grandmaster function

● Fits into any Output card slot

● OSA 5548C SSU-E60 : up to 6 TCC-PTP cards

● OSA 5548C SSU-E200 : up to 20 TCC-PTP cards PTP Hub

OSA 5548C SSU-E60 OSA 5548C SSU-E200

v.1.2 11/10/12 ∙ BIGR slide № 51

OSA 5548C “PTP HUB”

CAPACITY (20 GM blades per shelf) in Unicast or Multicast

● with TCC-PTP GM

● More than 2’500 slaves per shelf

● with TCC-PTP II GM *

● More than 5’000 slaves per shelf

* Available in 2013

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TESTING

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Test Case 13 - Sudden large and persistent changes in

network load

● Test Case 13 models sudden large and persistent changes in network load. It demonstrates stability on sudden large changes in network conditions, and wander performance in the presence of low frequency PDV.

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Test case 13 - Results

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Test Case 14 - Slow change in network load over an

extremely long timescale

● Test Case 14 models the slow change in network load over an extremely long timescale. It demonstrates stability with very slow changes in network conditions, and wander performance in the presence of extremely low frequency PDV.

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Test case 14 – Results with Traffic model 1

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Test case 14 – Results with Traffic model 2

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Network Traffic Model 1 (majority of traffic is Voice)

Network Traffic Model 2 (majority of traffic is Data)

Network Traffic Models

● The access traffic is composed of conversational (voice), streaming (audio-video), interactive (http) and background (sms, e-mail):

● 80% of the load must be minimum size packets

● 15% of the load must be maximum size packets

● 5% of the load must be medium size packets

● Maximum size packets will occur in bursts lasting between 0.1 s and 3 s.

● 60% of the load should be based on packets of maximum size, and 40% on packets with a mix of minimum and medium size:

● 60% of the load must be maximum size packets

● 30% of the load must be minimum size packets

● 10% of the load must be medium size packets

● Maximum size packets will occur in bursts lasting between 0.1 s and 3 s.

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NETWORK EXAMPLES

Chapter 5

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Egy élö példa

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Egy europai példa

v.1.2 11/10/12 ∙ BIGR slide № 62

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● www.oscilloquartz.com

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