Extending the precision time protocol to a metropolitan area...

Degree project inCommunication Systems

Second level, 30.0 HECStockholm, Sweden

M O Z H D E H K A M E L

Synchronizing radio base stations

Extending the precision time protocolto a metropolitan area network

K T H I n f o r m a t i o n a n d

C o m m u n i c a t i o n T e c h n o l o g y

Extending the precision time protocol to a metropolitan area network

Synchronizing radio base stations

Mozhdeh Kamel

2014.02.06

Master thesis

Examiner: Gerald Q. Maguire Jr. Supervisors: Jiang Wu

School of Information and Communication Technologies KTH Royal Institute of Technology

Stockholm, Sweden

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Abstract

When building various types of wide area cellular radio networks there is a need to synchronize all of the base stations within a given system. Today this is typically done by attaching a highly accurate clock to each radio base station. A GPS radio receiver is commonly used as such a clock. This thesis explores the use of the Precision Time Protocol (PTP) to provide synchronization of radio base stations, rather than the current practice of using GPS radio receivers.

Advantages of utilizing PTP rather than a GPS radio receiver include the ability to easily locate radio base stations (without the need for connecting the GPS radio receiver to an antenna that has line of sight to a sufficient number of GPS satellites); the system is not vulnerable to interference with or jamming of GPS radio signals; the system is not vulnerable to spoofing of GPS radio signals, and because the new generations of radio base stations are connected to a packet based backhaul link – the system can potentially utilize the existing packet network interface (thus avoiding the need for a serial interface to the GPS receiver and a pulse per second input).

At the start of this thesis project it was not known what the limits of PTP are (in terms of utilizing PTP together with radio base stations). Thus it was not clear whether PTP could be extended to much longer distances than it had originally been designed for.

This thesis shows that PTP can be used as an accurate timing source to synchronize base stations in networks with up to four switches between the PTP grandmaster and any PTP slave.

This project was performed in the Common Transport Feature department at Ericsson.

Keywords: precision time protocol, radio base station, synchronization

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Sammanfattning

Vid konstruktion av wide area cellular radio networks finns det behov av att synkronisera samtliga basstationer inom ett givet system. Detta görs idag typiskt genom att ansluta en klocka med stor tillförlitlighet till varje basstation. En GPS radiomottagare används vanligen som klocka för detta syfte. Detta examensarbete undersöker användandet av Precisions Tid Protokoll (PTP) för att synkronisera radiobasstationer, istället för att som nu typiskt använda GPS radiomottagare.

Fördelar med att använda PTP istället för GPS radiomottagare är att en radiobasstation lätt kan lokaliseras (utan att ansluta en GPS-mottagare till en antenn vilken har mottagning mot flera GPS-satelliter); systemet är inte sårbart mot interferens eller störningar av GPS radio signaler; systemet är inte sårbart mot spoofing av GPS radio signaler och på grund av att den nya generationens radiobasstationer är anslutna till ett paketförmedlande backhaul nätverk kan systemet potentiellt använda sig av det redan existerande paketförmedlande nätverksgränssnittet (och på sätt undvika ett seriellt gränssnitt mot en GPS-mottagare och en puls per sekund ingång).

När detta examensarbete startades var det inte känt var gränserna för PTP låg när det gäller att använda PTP tillsammans med radiobasstationer. Det var således inte klart ifall räckvidden för PTP kunde utvidgas till mycket längre avstånd än det ursprungligen var ämnat för. Detta examensarbete syftar till att visa att PTP kan användas som tillräckligt noggrann synkroniseringskälla för basstationer i nätverk med upp till fyra nätverksswitchar mellan PTP Grand Master och PTP slav.

Examensarbetet har utförts vid avdelning Common Transport Feature på Ericsson.

Nyckelord: precisions tid protokoll, radiobasstation, synkronisering

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Acknowledgement

I would like to express my gratitude to my academic supervisor and examiner at KTH, Professor Gerald Q. Maguire Jr. for guiding me during this thesis project, providing helpful feedback and ideas during this thesis project.

I also would like to thank my industrial supervisor and my manager in Ericsson Jiang Wu and Sheng Chu Li and who gave the opportunity to do this thesis at Ericsson AB. I would also like to thank Mikael Johansson and Mikael Olofsson in the Network Synchronization department for explanation about PTP protocol and current synchronization technologies. Moreover, I like to thank to Seth Norgren, Thomas Bäverlid and Goran Matovic in CTF lab for lending me necessary equipment for this thesis process.

Furthermore, I like to special thanks to my friend Pooya Moazzeni Bikani for supporting me spiritually throughout my thesis.

Last but not least, many thank to my parents and my sisters for their unconditional support and love throughout my life.

Tab

AbstractSammanAcknowlTable of List of FList of TList of A

11.1 1.2 1.3 1.4

1.4.1.4.1.4.1.4.

1.5

22.1

2.1.2.1.

2.2 N2.2.2.2.2.2.

2.3 2.3.2.3.2.3.2.3.2.3.2.3.2.3.2.3.2.3.2.3.2.3.

2.4 A2.4.2.4.2.4.2.4.2.4.

2.5 2.5.2.5.2.5.2.5.

ble of C

t ....................nfattning ......ledgement ....

f Contents .....Figures ..........Tables ............Acronyms and

IntroductionOverview .....Goals ............Limitations ...Methodology

Literat.1 Experi.2 Data C.3 Conclu.4

Structure of th

Background Requirements

Base s.1 Base s.2

Network time NTP’s.1 NTP v.2 Simple.3

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Peer d.10 Metrop.11

Available Syn Time E.1 Time I.2 Maxim.3 Time D.4 Modifi.5

Related work IEEE 8.1 IEEE 1.2 Synchr.3 Other .4

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33.1 N

3.1.3.1.3.1.

3.2 3.2.3.2.3.2.

3.3 3.4

3.4.3.4.3.4.3.4.

44.1 4.2

4.2.4.2.4.2.

4.3 4.3.4.3.4.3.4.3.4.3.4.3.4.3.4.3.4.3.

4.4 4.4.4.4.

4.5

A55.1

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5.2 5.2.5.2.

5.3

66.1 6.2 6.3

ReferencAppendiAppendi

Method ........Network Con

Switch.1 Netwo.2 Traffic.3

Simulation ... Netwo.1 OMNE.2 OPNE.3

Emulation ....Experimental

Goals .1 Enviro.2 Scenar.3 Netwo.4

Design and ISimulation wTestbed ........

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Emulating net Delay .1 Packet.2

Data Collectio

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Conclusions Conclusions .Future work .Required refle

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ix

List of Figures

Figure 1-1: PTP over MAN............................................................................................................................ 2 Figure 2-1: General protocol architecture for IEEE1588 ............................................................................... 9 Figure 2-2: Software-based PTP functions .................................................................................................. 10 Figure 2-3: FPGA-based PTP functions ....................................................................................................... 11 Figure 2-4: Microcontroller-based PTP functions ........................................................................................ 11 Figure 2-5: PTP component in network, adapted from [28] ........................................................................ 13 Figure 2-6: PTP header format ..................................................................................................................... 15 Figure 2-7: Master-Slave message exchange in PTP-v1, adapted from [17] ............................................... 17 Figure 2-8: Message exchange with end to end transparent clock, adopted from [16] ................................ 18 Figure 2-9: Message exchange with peer to peer transparent clock, adopted from [14] .............................. 18 Figure 3-1: Traffic Management System (adapted from [34]) ..................................................................... 27 Figure 3-2: BC emulation design ................................................................................................................. 29 Figure 3-3: Overview of network scenario in the experimental study ......................................................... 31 Figure 3-4: GM andslave connected via virtual bridge ................................................................................ 34 Figure 4-1: Suggested new PTP engine process .......................................................................................... 36 Figure 4-2: Scenario 0 topology ................................................................................................................... 38 Figure 4-3: Scenario 1 topology ................................................................................................................... 39 Figure 4-4: Scenario 2 topology ................................................................................................................... 40 Figure 4-5: Scenario 3 topology ................................................................................................................... 42 Figure 4-6: Scenario 4 topology ................................................................................................................... 43 Figure 4-7: Scenario 5 topology ................................................................................................................... 45 Figure 4-8: Scenario 6 topology ................................................................................................................... 46 Figure 4-9: Scenario 7 topology ................................................................................................................... 48 Figure 4-10: Scenario 10 topology ................................................................................................................. 49 Figure 4-11: GM and slave connected with virtual bridge ............................................................................. 51 Figure 5-1: Delay variation, 100usec delay added to network ..................................................................... 56 Figure 5-2: Delay variation in different amount of delay added betwen GM and slave while

connected through virtual bridge ............................................................................................... 57 Figure 5-3: Absolute value of delay variation between GM and slave while they connected

together through virtual bridge .................................................................................................. 57 Figure 5-4: Delay variation, GM and Slave facing different amount of packet loss .................................... 58 Figure 5-5: Abstract value of delay variation, GM and Slave facing different amount of packet

loss ............................................................................................................................................ 59 Figure 5-6: Packet loss in different profiles, five nodes between GM and slave ......................................... 60 Figure 5-7: Packet loss as captured by traffic generator in profiles 3 and 8, with 5 nodes between

GM and slave ............................................................................................................................ 61 Figure 5-8: PTP PDV, five nodes between GM and slave, no traffic in the network .................................. 61 Figure 5-9: Histogram, five node between GM and slave, no traffic in the network ................................... 62 Figure 5-10: PTP GM and Slave versus relative time at sniffer, five node between GM and Slave,

no traffic in the network ............................................................................................................ 62 Figure 5-11: Delta PTP GM and slave versus relative time at sniffer, five nodes between GM and

Slave, no traffic in the network ................................................................................................. 63 Figure 5-12: Delta GM and slave versus delta relative time, five node between GM and Slave, no

traffic in the network ................................................................................................................. 63 Figure 5-13: TE between GM and Slave while no traffic running ................................................................. 64 Figure 5-14: Absolute value of delay variation – No traffic running ............................................................. 65 Figure 5-15: Delay varioation when there is no traffic in the networks, no delay_req and

delay_resp ................................................................................................................................. 66 Figure 5-16: Delay Variation in Different Profile load, No node between GM and Slave ............................ 67 Figure 5-17: Absolute value of delay variation in scenario 0 ........................................................................ 68 Figure 5-18: Delay Variation in Different Profile load, one node between GM and Slave ........................... 69 Figure 5-19: Absolute value of delay variation in different profile load, one node between GM

and Slave ................................................................................................................................... 69 Figure 5-20: Delay Variation in Different Profile load, two node between GM and Slave ........................... 70 Figure 5-21: Absolute value of delay variation, two nodes between GM and Slave ..................................... 71 Figure 5-22: Delay Variation in Different Profile load, three node between GM and Slave ......................... 72

x

Figure 5-23: Absolute value of delay variation, three node between GM and Slave ..................................... 72 Figure 5-24: Delay Variation in Different Profile load, four node between GM and Slave........................... 74 Figure 5-25: Absolute value of delay variation , four nodes between GM and slave .................................... 74 Figure 5-26: Delay Variation in Different Profile load, five node between GM and slave ............................ 75 Figure 5-27: Absolute value of delay variation, five nodes between GM and slave ...................................... 76 Figure 5-28: Delay Variation in Different Profile load, six node between GM and slave ............................. 77 Figure 5-29: Absolute value of delay variation – six nodes between GM and slave ..................................... 77 Figure 5-30: Delay Variation in Different Profile load, seven node between GM and slave ......................... 78 Figure 5-31: Absolute value of delay variation, seven nodes between GM and slave ................................... 79 Figure 5-32: Delay Variation in Different Profile load, ten nodes between GM and Slave ........................... 80 Figure 5-33: Absolute value of Delay Variation in Different Profile load, ten nodes between GM

and Slave ................................................................................................................................... 80

xi

List of Tables

Table 2-1: Synchronization accuracy required of various radio standards (inspired by the table in [3]) ........................................................................................................................................... 5

Table 2-2: PTP messages type and specification ........................................................................................ 15 Table 2-3: Header fields of the PTP packets [26] ....................................................................................... 16 Table 3-1: PTPd vs Linux PTP project ....................................................................................................... 28 Table 3-2: Hardware Specification ............................................................................................................. 30 Table 3-3: Network Interface Card (NIC) Specification ............................................................................. 30 Table 3-4: Summary of Scenarios and Tests (with × indicating a combination of number of

nodes and load that was tested) ................................................................................................. 32 Table 3-5: Traffic pattern and traffic load specification ............................................................................. 33 Table 4-1: PTP node specification .............................................................................................................. 37 Table 4-2: Channel configuration of the osciloscope ................................................................................. 37 Table 4-3: Scenario 0 test description ......................................................................................................... 38 Table 4-4: Scenario 1 test description ......................................................................................................... 39 Table 4-5: Link bandwidth in scenario 2 .................................................................................................... 40 Table 4-6: Scenario 2 tests description ....................................................................................................... 41 Table 4-7: Link Bandwidth in scenario 3 ................................................................................................... 42 Table 4-8: Scenario 3 tests description ....................................................................................................... 42 Table 4-9: Link Bandwidth in scenario 4 ................................................................................................... 44 Table 4-10: Scenario 5 tests description ....................................................................................................... 44 Table 4-11: Link Bandwidth Scenario 5 ....................................................................................................... 45 Table 4-12: Scenario 5 tests description ....................................................................................................... 45 Table 4-13: Link Bandwidth scenario 6 ........................................................................................................ 46 Table 4-14: Scenario 6 tests description ....................................................................................................... 47 Table 4-15: Link Bandwidth scenario 7 ........................................................................................................ 48 Table 4-16: Scenario 7 tests description ....................................................................................................... 48 Table 4-17: Link Bandwidth scenario 8 ........................................................................................................ 50 Table 4-18: Scenario 8 tests description ....................................................................................................... 50 Table 4-19: Amount of delay manually added.............................................................................................. 52 Table 4-20: Profile ecplanation - Emulationg paclet loss ............................................................................. 52 Table 5-1: Standard variation, Delay added while GM and slave connected through virtual

bridge ........................................................................................................................................ 58 Table 5-2: Standard variation in different profile, GM and slave connected through virtual

bridge and facing packet loss .................................................................................................... 59 Table 5-3: Standard Deviation .................................................................................................................... 65 Table 5-4: Delay Variance in different vendors .......................................................................................... 65 Table 5-5: Test topologies baased on number of nodes .............................................................................. 66 Table 5-6: Standard deviation of delay variation with different load profiles- Scenario 0 ......................... 68 Table 5-7: Standard deviation of delay variation with different load profiles, Scenario 1 ......................... 70 Table 5-8: Standard deviation of delay variation with different load profiles, Scenario 2 ......................... 71 Table 5-9: Standard deviation of delay variation with different load profiles, Scenario 3 ......................... 73 Table 5-10: Standard deviation of delay variation with different load profiles, Scenario 4 ......................... 75 Table 5-11: Standard deviation of delay variation with different load profiles, Scenario 5 ......................... 76 Table 5-12: Standard deviation of delay variation with different load profiles, Scenario 6 ......................... 78 Table 5-13: Standard deviation of delay variation with different load profiles, Scenario 7 ......................... 79 Table 5-14: Standard deviation of delay variation with different load profiles, Scenario 10 ....................... 81 Table 5-15: Synchronizarion result for different number of nodes between GM and Slave in

different load profile .................................................................................................................. 81 Table 6-1: D-link switch specification ........................................................................................................ 91 Table 6-2: HP switch specification ............................................................................................................. 92 Table 6-3: NETGEAR switch specification ............................................................................................... 93 Table 6-4: Westermo switch specification .................................................................................................. 94 Table 6-5: Mean, maximum and minimum delay variation (in microseconds), GM and slave

connected through virtual bridge and facing different amount of delay(in microsecond). ............................................................................................................................ 95

xii

Table 6-6: Mean, maximum and minimum delay variation (in microseconds), GM and slave connected through virtual bridge and facing different percentageous of packet loss. ............... 95

Table 6-7: Mean delay variation (in microseconds) with different numbers of nodes between GM and slave with different load profiles. ................................................................................ 96

Table 6-8: Minimum Delay variation(in microseconds) with different numbers of nodes between GM and slave with different load profiles. .................................................................. 97

Table 6-9: Maximum Delay variation(in microseconds with different numbers of nodes between GM and slave with different load profiles. .................................................................. 98

xiii

List of Acronyms and Abbreviations

Advanced LTE Advanced Long Term Evolution AOCM Adaptive Oscillator Correction Method BC Boundary Clock BMC Best Master Clock CDMA Code Division Multiple Access CPU Central Processing Unit FDD Frequency Division Duplexing FIFO First In First Out FPGA Field-Programmable Gate Array GB Ggigabyte GHz Ggigahertz GM Grandmaster GPS Global Positioning System GSM Global System for Mobile LAN Local Area Network LTE Long Term Evolution MAC Media Access Control MAN Metropolitan Area Network Mbps Megabits per second MIB Management Information Base minTDEV Minimum Time Deviation ms Millisecond NA Not Applicable NS Nanosecond NTP Network Time Protocol OC Ordinary Clock OCXO Oven-Controlled Crystal Oscillator OS Operating System PCI Peripheral Component Interconnect. PLL Phased Locked Loop PPB Pulse per Billion PPM Pulse per Million PPS Pulse per Second PQ Priority Queuing PRC Primary Reference Clock PIM-SM Protocol Independent Multicast-Sparse Mode PTP Precision Time Protocol PTPD Precision Time Protocol Daemon QoS Quality of Service RBS Radio Base Station RTC Real-Time Clock RP Rendezvous Point SNMP Simple Network Management Protocol Sync-E Synchronous Ethernet TC Traffic Control TC Transparent Clock

xiv

TDD Time Division Duplexing TDev Time Deviation TDM Time Division Multiplexing TLV Type-Length-Value UDP User Datagram Protocol UMTS Universal Mobile Telecommunications System UTC Coordinated Universal Time WAN Wide Area Network WCDMA Wideband Code Division Multiple Access WiMAX 2G

Worldwide Interoperability for Microwave Access second generation

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Different types of RBS (e.g., GSM, Wideband Code Division Multiple Access (WCDMA), and Long Term Evolution (LTE)) have different timing requirements (these requirements will be described in detail in section 2.1.1). While PTP can normally meet these timing requirements in a local area network (LAN), in this thesis project we will examine whether PTP can meet these requirements in a MAN. To do this we will explicitly calculate a delay budget and examine the expected jitter in a MAN to which the various RBSs are attached. The main scientific question of this thesis project is to understand how well PTP can keep the slave within a bounded time of the GM and for what period of time the slave is within this bound.

1.3 Limitations This section states the limitations of this thesis with respect to the study and

implementation that have been carried out within this project.

Initially, the planned thesis was to include a comparison between a simulation of the PTP protocol and experimental results using real hardware. However, after several months of working with a PTP implementation in OPNET, this effort was terminated because some parts of the code were missing and unavailable from the original author of the code.

Following this the thesis aim shifted to an experiment with both full time aware networks and partial time aware networks. Unfortunately, budget limitations prevented the acquisition of a real hardware boundary clock (BC) or the emulation of a BC.

As a result the experiments were done with older borrowed PTP devices that do not support PTPv2 (which is currently used in market). Moreover, those devices only support a special kind of GPS receiver. As a result the experiments were limited to measuring the time difference between a GM and slave where the GM stratum is 255 instead of 1. This means that the GM did not have a GPS disciplined oscillator and this GM was not synchronized with UTC; the results is that it was only possible to measure the relative deviation of the slave from this GM, rather than the absolute deviation from UTC.

A further limitation of this thesis was that the industrial team, I was working with, did not have any competence in the area of synchronization; hence I have done this thesis completely independently. Having a larger budget and support from team mates, who had competence in synchronization would have been helpful and reduced the time necessary to carry out this thesis project.

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1.5 Structure of this thesis The first chapter of this thesis has presented the problem that is to be solved. Chapter 2

provides the reader with the necessary background to read the rest of the thesis. Chapter 2 also summarizes related work that is directly relevant to this thesis. Chapter 3 describes the method and methodology used. Chapter 4 describes the design and implementation of a prototype solution. Chapter 5 evaluates this prototype with the goal of determining the bounds of operation for PTP with respect to the requirements for synchronization of different types of RBSs. Chapter 6 summarizes the conclusions that can be drawn from this thesis project, proposes future work, and offers reflections on some of the economic, social, and ethical considerations relevant to this thesis project.

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ultiple PTP his clock is

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ed to PTP indevice. Theinterval delrespect to dclocks can nsparent clnterval delaforming in es propagatevents a qu

ence in the c

e network ealso helps

ents that imaster clock

Figure 2-5ocks are de

manent clocally this clo

port that actas a mas

ter Clock (B

ports that ausually a s

ng for the sechosen by Bore accurateto synchron

n version twmain task

lay into thdelay compact as peerlocks. An ay for end-to

the systemtion delay ueue from fcase of a cha

elements anto visualize

nteract in k (GM), ord5 shows thescribed bel

ck in the sysock will util

ts as an endster or slavBMC) algor

acts as a trantandard swiegments tha

BMC to act e clock. Thnize other cl

wo. These dk of this tyhe system; ensation an

r-to-peer traend-to-end

o-end systemm. A peer-trather than forming anange in the

nd PTP come the master

order to rdinary cloce PTP mastlow [26, 27

ystem is knolize a GPS

d device is cve in the rithm which

ansmission ditch or a rouat it is conneas a slave t

he other porlocks which

devices can ype of nodthis impro

nd accuracyansparent c

d transparenms, thus preto-peer tran

n an intervand helps to

network [2

mponents ner-slave rela

achieve ck (OC), ter-slave ] (based

own as a receiver

called an network

h will be

device is uter that ected to. that will ts of the h will be

act as a de is to oves the y. In the locks or nt clock eventing nsparent al delay,

provide 1, 27].

eeded to ationship

Figure 2

2.3.5

Besnot invofor eachclock w

In PThese a

Straprimaryeither a

Strareferenc

Stra(greater

Stra

Straclock [1

2-5: PTP

Best Mast

t Master Clolve TCs. Th communi

with higher a

PTP, clocksaccuracies a

atum 1 hasy reference an atomic cl

atum 2 hasce in a PTP

atums 3 anr than 100 n

atums 5-25

atum 255 i18].

P component

ter Clock S

lock (BMCThe main tacation link.accuracy an

s are categoare specified

s an accuracclock. Thisock or a GP

an accuracnetwork [1

nd 4 can bnanoseconds

54 are reserv

is a clock w

t in network

Selection

) is a distriask of the a. For each c

nd the slave

orized accod as:

cy of withins clock is cPS receiver

cy of within8].

be consideres) [18].

ved [18].

with a defau

k, adapted fr

ibuted algoralgorithm iscommunicais a node th

ording to th

n 25 nanoseconsidered t[29].

n 100 nanos

ed as other

ult setting a

from [28]

rithm that ins to define mation link thhat should b

heir accurac

econds. A sto be a gran

seconds. Th

r references

and can nev

nvolves BCmaster and

he master wbe synchron

cy by differ

tratum 1 clondmaster cl

is clock wil

at a lower

ver be cons

Cs and OCsslave relat

will be the pnized [29].

rent stratum

ock is conslock and is

ll be a seco

r level of a

sidered as a

13

; it does ionships port of a

m levels.

sidered a s usually

ond level

accuracy

a master

14

2.3.6

PTPand slavinclude

In Pmessagorigin ctimestamthe mesclock up

FollFollow_origin tand incPTP v1

In PmessaginformaselectioPTP in messaginfrequesynchro

PdemessagPdelay_

2.3.7

Tabdetail inhave thspecific

Messages

P is a synchve clocks. Tan origin ti

PTPv1, the ee is sent byclock timesmp of this sssage deparp to date.

low_up, D_up messagtime stamp.cludes the d will be exp

PTP versiones. The Anation was ion leads to a

the netwoe. This reflently and tonization.

elay_resp, Pes in PTPv2_resp and Pd

PTP mess

ble 2-2 shown section 2.he same hcation of eac

s in PTP

hronization These messimestamp) a

event messay a master. Tstamp. A Dslave clock.rts the node

Delay_resp, ge is sent b. A Delay_rdelay receipplained in se

n 2, Pdelaynnounce meincluded ina smaller Syork. The Sylects the asthat the pr

Pdelay_follo2. The Signdelay_follo

sage packe

ws summary.3.5. Each m

header. Heach field in t

protocol wages can beand general

ages are: (1This messagDelay_req m. An origin e. A Sync m

and Manby a masterresp messag

pt timestampection 2.3.8

y_req and Aessage is ren Sync meync messageync messagsumption th

rimary purp

ow_up, and alling messw_up mess

et format

y of messagmessage coader formathe header fi

which relies e categorizel messages.

) Sync mesge includesmessage istimestamp

message wil

nagement mr right afterge is sent bp. The com

8.

Announce mesponsible fssage. Usine, this can de will be shat the netwpose of the

Signalling sage is used ages are use

ge types in Pontains headt is shown

field of the P

on messaged into two

ssage and (2 best maste

s sent by ais the local ll be sent p

messages r a Sync mby the mast

mmunication

messages wfor best mang a differdecrease thesend more work and se protocol

messages wto send add

ed in the ne

PTP and theder, suffix an in FigurePTP packets

ges exchangtypes: even

2) Delay_reer selection a slave clocnode’s cloceriodically

are generaessage and ter in responn between m

were added aster selectirent message amount of frequently et of clockis to provi

were added ditional dataew peer dela

eir purpose and body. Ae 2-6. Tabs [30].

ged betweennt messages

eq message.informationck with thck value at to keep the

al messaged includes a

nse to a Demaster and

to the set oion. In PTPge for bestf bandwidth than an An

ks change revide accurat

d to the set a using TLVay mechanis

which discAll of the mble 2-3 sho

n master s (which

A Sync n and an e origin the time

e slave’s

es. The a precise elay_req slave in

of event Pv1, this t master used by

nnounce elatively te clock

of event V tuples. sm [18].

ussed in messages ows the

Table 2-

Figure 2

Messag

Messagpurpos

UDP po

-2: PTP

2-6: PTP

e

ge name SD

ges se

gttns

ort p

P messages t

P header for

event mess

Sync Delay_Req

generate antransport timestamps needed for tsynchronisa

port 319

type and spe

rmat

ages genmeFolDe

d

the ation

usethebetclo

po

ecification

neral essages llow_Up lay_Resp

ed to measue link delay tween two ocks

ort 320

annomess

ure buildsynchhierar

unce age

up the hronization rchy

signalinmessage

all otherpurpose

15

ng es

r s

16

Table 2-3: Header fields of the PTP packets [26]

Field value Explanation Octets Offset

Transport Secific 0 IEEE1588 PTP message 0.5 0

1 802.1AS PTP message 0.5 0 Message type 0 Sync message 0.5 0

1 Delay_req message 0.5 0

2 Pdelay_req message 0.5 0

3 Pdelay_resp message 0.5 0

4-7 Reserved 0.5 0

8 Follow_up message 0.5 0

9 Delay_Resp message 0.5 0

A Pdelay_Resp_Follow_up ,essage 0.5 0

B Announce message 0.5 0

C Signalling message 0.5 0

D Management message 0.5 0

E-F Reserved 0.5 0

Version PTP Version of IEEE1588 0.5 1

Message length Length of PTP message 2 2

Domain Number It shows the number of domain the PTP message sender belong to

1 4

Correction Field This is a correction value which is ns multiplied by 216

1 5

Source Port Identity Indicates clock ID and port which the message sent

10 16

Sequence Id Indicates the sequence number of PTP message which relate the messages together

2 30

Control Field It uses for compatibility to IEEEv1. Different by messages.

1 32

Log Message Interval Indicates the interval of PTP messages 1 33

2.3.8

In Pdelay m2-7 sho

Figure 2

s1 =

m1

s2 =

m2=

t(M

t(sla

2.3.9

PTPsender-rbe usedmessagtranspar

Delay Com

PTPv1, the mechanism i

ws how me

2-7: Mas

= slave rece

= master se

= slave send

= master rec

Master-Slave

ave-Master)

Delay req

P was desigreceiver de

d to computes are excrent clock.

mputation

delay requeis another dessages are e

ster-Slave m

ives Master

ent the Mast

ds a request

ceives the re

) = s1-m1

) = m2-s2

Delay =t(M

uest-resp

gned for symlay is equale end-to-en

changed be

m2

m1

Ma

est-responsedelay compuexchanged b

message exch

r Timestamp

ter Timestam

at this time

equest at thi

Slav-Master

onse mec

mmetric appl to receive

nd delay bettween a m

aster

e mechanisutation methbetween the

hange in PTP

p at this tim

mp at this ti

e

his time

2t(slave ave) +

hanism

plications; ser-sender detween transpmaster and

Sync

m1

Follow_up

Delay_req

Delay_resp

m2

m is used fhod that wae master and

P-v1, adapte

me (via a Syn

ime (includ

Master)-e

so the delayelay. In PTPparent clockslave with

Sl

for computias introduced slave to co

ed from [17]

nc message

ded in Follow

y computatioP v2, this mks [18]. Figh an interm

s2

s1

ave

ing delay. Ted in PTPv2ompute dela

]

e)

w_up messa

Equ

on assumesmechanism gure 2-8 shomediate end

17

The peer 2. Figure ay.

age)

uation 2-1

that the can also

ows how d-to-end

18

Figure 2

2.3.10

Thea peer-tthis memessagdelay be

Figure 2

2-8: Mes

Peer delay

e peer delay to-peer TC. echanism. es do not hetween two

2-9: Mes

m2

Master

m1

Tra

ssage exchan

y mechan

mechanismPdelay_req

In contrasthave to be fo nodes [18]

ssage exchan

mDela

r

Syn

Follow

Delay

m1

tcA1

tcA2

ansparent ClDelay req

nge with end

ism

m is used whq, Pdelay_ret to the deforwarded a. Figure 2-9

nge with pee

m2 ay_resp

nc

w_up

y_req

T

Pdelay_( tcB

Pdelay_

ock A (TCA)uester

Pdela

d to end tran

hen computesp, and Pdelay requesand are sim9 shows this

er to peer tr

Transparent

_follow_up B1, tcB2)

_req

Tra

ay_resp

nsparent clo

ting the deladelay_followst-response

mply used ins mechanism

ansparent c

m2

Delay

Clock

Syn

Follm

Delay_req

tcB

tcB

ansparent CloDelay resp

ock, adopted

ay between w_up messa

mechanismn measuringm in more d

clock, adopte

y_resp

nc

low_up m1

2

1

ock B (TCB) ponder

d from [16]

two OCs, Bages are invm messageg the point-detail.

ed from [14

Slave

s1

BCs, and volved in s, these -to-point

]

tcA

tcB

tcB2

tcA2

Tranclock Athe enddelay ca

t(req

t(res

2.3.11

A mKilomeacross afrequen

Groaggregaaggrega

2.4 AIn t

the twoThen, tr(TDEV

2.4.1

TE time. TE

1 = the time

1 = the time

2 = the time

2 = the time

nsparent cloA (TCA)’s rd of this mean be calcul

quester-resp

sponder-req

Delay

Metropoli

metropolitanetres [24]. Aa city. A Mntly used to

oups of nodeate, and corate part is th

Availablethis section o traditionalraditional c

V), will be de

Time Erro

is a functioE is shown

e TCA send

e TCB recei

e TCB respo

e TCA rece

ock B (TCBresponse. Tessage exchlated as:

ponder) = tc

quester) = tc

y = t(reques

tan Area N

n area netA MAN can

AN is usuaconnect bro

es in a MANre. An accehe middle pa

e Synchrothe availab

l metrics timclock metricescribed.

or

on that calcis in equati

ds a Pdelay_

ives the requ

onds to Pde

ives the resp

B) sends theThis Pdelay_hange, TCA

cB1-tcA1

cA2-tcB1

respond-rste

Network

work (MAbe used for

ally made upoadband net

N can be claess network art that conn

onizationble metricsme error (Tcs, Maximu

culates the don 2-3[32].

_req

quest from T

elay_req

ponse

e Pdelay_fo_follow_up

A is aware o

2t(resp der) +

AN) [31] spr communicp of severaltwork subsc

assified acck is the partnects the co

n Metricsin network

TE) and timum Time In

difference i

TCA

ollow_up afp message cof tcA1, tcA

requ-erpond

pans a largcation betwl LANs concribers to a l

cording to tht of a MANore network

s k synchronizme interval nterval Error

in time valu

fter respondcontains tcBA2, tcB1, a

uester)

ge area of een multipl

nnected via blarger netwo

he followingN closest to

to the acce

zation will error (TIE)r (MTIE) a

ues of two

ding to TranB1 and tcB2and tcB2. T

Equ

f between 5le buildingsbridges. A

work such as

g hierarchy the custom

ess network(

be explaine) will be diand Time D

clocks at a

Equ

19

nsparent 2. So, at Thus the

uation 2-2

5 to 50 s or even MAN is WAN.

: access, mer. The (s).

ed. First scussed.

Deviation

a certain

uation 2-3

20

2.4.2

TIEtwo diff

Where:

local cloto calcu[33].

2.4.3

MTtime. Ea

Where:

Time Inte

E (shown infferent times

tisaceπcertaiTIE and TEock to a refulate the fre

Maximum

TIE is a metach period’

, num

erro

inde

total time

erval Error

n equation 2s (as shown

,ertaintime; nperiodofiE are traditference clocequency erro

m Time Inte

tric that mes time inter

mber of samp

or sampling in

ex of the spec

l number of

e error sampl

r

2-5) computin equation

T(t+π

interval; tional metrick (in order or using TI

erval Erro

easures the val error ca

le within a c

nterval;

cial period o

samples;

le;

tes the timen 2-4 [32]).

π)-T(t)

ics that can to perform

IE metrics b

or

maximum an be associ

certain period

over the data;

e difference

be used tophase synch

by calculatin

interval erated with a

d;

;

e between t

o measure thhronizationng the slope

ror during sliding win

,

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Equ

Equ

he phase ern). It is also e of a curve

a certain pndow.

, , . . ,

values at

uation 2-4

uation 2-5

rror of a possible e of TIE

period of

Equuation 2-6

2.4.4

Minwhich iwhether

,

2.4.5

MDfrequeninterval

2.5 RAfte

Timing Networstandardactuallyexplain in more

Somthese ar

2.5.1

IEEapplicatbased omechan

Managmechan

Path de

Time Devi

nimum Timis independer the networ

, …Modified A

DEV is a trncy by reducl into n cy

Related wer PTPv2, t

and Syncrks” standard has the stry for time

how PTP we detail.

me experimere explained

IEEE 802.

EE 802.1AStions such on IEEE 1nisms of this

gement nism

elay mecha

iation/ mi

me Deviationent of the nrk meet a sy

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work the IEEE 80chronizationrd based onring “for LAsensitive awill operate

ents have bd in more de

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1588 v2 ans PTP profi

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lgorithm deal observatieriod [34].02.1AS “Stan for Timn the seconAN and metpp

Extending the precision time protocol to a metropolitan area...

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