extending the precision time protocol to a metropolitan ...maguire/degree-project... ·...
TRANSCRIPT
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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
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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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© Mozhdeh Kamel, February 2014
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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.
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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
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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.
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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
Precision time Differe.1 PTP O.2 PTP S.3 Compo.4 Best M.5 Messag.6 PTP m.7 Delay .8 Delay .9
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
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3.2 3.2.3.2.3.2.
3.3 3.4
3.4.3.4.3.4.3.4.
44.1 4.2
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4.3 4.3.4.3.4.3.4.3.4.3.4.3.4.3.4.3.4.3.
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ReferencAppendiAppendi
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Emulation ....Experimental
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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
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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
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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
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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
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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
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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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Figure 1-1: PTP over MAN
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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-
4
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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-
10
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-
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clock (TC).types of clo
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single PTP pck can act e Best Mastction 2.3.5.
ultiple PTP his clock is
precise timinne port is cd with a moas masters t
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
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n an intervand helps to
network [2
mponents ner-slave rela
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own as a receiver
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h will be
device is uter that ected to. that will ts of the h will be
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eeded to ationship
-
Figure 2
2.3.5
Besnot invofor eachclock w
In PThese a
Straprimaryeither a
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2-5: PTP
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with higher a
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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].
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s an accuracclock. Thisock or a GP
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Selection
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orized accod as:
cy of withins clock is cPS receiver
cy of within8].
be consideres) [18].
ved [18].
with a defau
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n 100 nanos
ed as other
ult setting a
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rithm that ins to define mation link thhat should b
heir accurac
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r references
and can nev
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he master wbe synchron
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tratum 1 clondmaster cl
is clock wil
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rent stratum
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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
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2.3.7
Tabdetail inhave thspecific
Messages
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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
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sage packe
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and Manby a masterresp messag
pt timestampection 2.3.8
y_req and Aessage is ren Sync meync messageync messagsumption th
rimary purp
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) Sync mesge includesmessage istimestamp
message wil
nagement mr right afterge is sent bp. The com
8.
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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
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m1
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m2
m is used fhod that wae master and
P-v1, adapte
me (via a Syn
ime (includ
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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
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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
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ay_resp
nsparent clo
ting the deladelay_followst-response
mply used ins mechanism
ansparent c
m2
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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
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]
-
tcA
tcB
tcB2
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Tranclock Athe enddelay ca
t(req
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2.3.11
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Metropoli
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ock B (TCBresponse. Tessage exchlated as:
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s k synchronizme interval nterval Error
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f between 5le buildingsbridges. A
work such as
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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].
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he phase ern). It is also e of a curve
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uation 2-4
uation 2-5
rror of a possible e of TIE
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-
2.4.4
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2.4.5
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2.5 RAfte
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2.5.1
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Related wer PTPv2, t
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how PTP we detail.
me experimere explained
IEEE 802.
EE 802.1AStions such on IEEE 1nisms of this
gement nism
elay mecha
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