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SYNCHRONIZATION IN PACKET SWITCHING
NETWORKS
USftARY
DIVERSITY CF MORATUWA, SR! LAtftfA
MORATUWA
Jayasinghe Mudiyanselage Rasika Chanaka Jayasinghe
(08/8371)
Dissertation submitted in partial fulfillment of the requirements for the degree 
Master of Science in Telecommunications
Department of Electronic and Telecommunication Engineering
University of Moratuwa 
Sri Lanka
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February 2014
/OS 98 2University of Moratuwa
108982
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I declare that this is my own work and this dissertation does not incorporate, without 
acknowledgement, any material previously submitted for a Degree or Diploma in any 
other University or institute of higher learning and to the best of my knowledge and 
belief it does not contain any material previously published or written by another 
person except where the acknowledgement is made in the text.
Also, I hereby grant to University of Moratuwa, Sri Lanka, the non-exclusive right to 
reproduce and distribute my dissertation, in whole or in part in print, electronic or 
other medium. I retain the right to use this content in whole or part in future works 
(such as articles or books).
Date: SU>lSignature:
The above candidate has carried out research for the Masters Dissertation under my 
supervision.
w
Signature of the supervisor: Date:
i
ABSTRACT
Network providers are faced with significant challenges in delivering backhaul solutions. 
Given that solutions based on Time Division Multiplexing (TDM), is not providing 
improved efficiency at a reasonable cost. Thus the need for new backhaul solutions is 
becoming significant. With the full-IP evolution, all the mobile networks are migrated to 
full-IP, thus capabilities inherent to traditional TDM needs to be developed in these IP 
networks. Real-time applications have relatively tight timing requirements concerning delay 
and delay variations. Therefore, need efficient timing solution for those real-time 
applications.
Synchronization is important aspect in networks and it is more critical in mobile networks. 
Loss of synchronization in mobile networks leads to call drops, mobile broadband data speed 
degrades and packet losses. Network equipment should be synchronized in frequency, time 
and time of day. To achieve the packet network based synchronization new strategies should 
be adopted. Else, traditional synchronization techniques is to be continued to synchronize 
networks.
Specialized synchronization networks can deliver better and accurate performances, but that 
is with a higher cost. There are new technologies introduced to the industry for 
synchronization. Before migrating in to new technologies, analyzing these techniques against 
the service delivery requirement is a prerequisite. There is information available and 
accessible for the operators, in the areas related to developments of technical standardization 
proceedings, but there is clear lack of resources and information for practical 
implementations.
There are gaps to be addressed while migration mobile networks into packet switching 
networks. Migration from circuit switching network to packet switching networks will break 
the synchronization chain. Most importantly, delivering the synchronization across the 
borders is required to interwork communication systems. Packet networks are asynchronous 
in nature therefore integrating time aware applications with packet network require correct 
timing at the interfaces to provide acceptable performance. Hence, special consideration and 
design is required in All-IP networks.
Cost plays a major role in the adaptation of modem technologies to existing 
telecommunication networks. Hence backhauling need to be a highly cost effective. At 
present, the IP networks have proven to be the most cost effective and thus migrating mobile 
network to a full-IP based network with synchronization capability provides additional cost 
benefit for the network operators.
In this research, technical standards and available synchronization methods are extensively 
evaluated. Moreover, network requirements, possibilities and limitations are also extensively 
analyzed. Logical behaviors are compared and analyzed for standardized synchronization 
techniques. Based on these analyses, implementation guidelines have been developed.
The guidelines have been prepared within the overall technical framework published by 
ITU-T standards and it is hoped that they will be helpful for the mobile operators who wish 
to migrate from existing network to future proof capacity agile packet switching network.
Keywords: Packet Networks, Synchronization, Synchronous Ethernet, IEEE 1588v2.
ii
DEDICATION
I would like to dedicate this dissertation to my wife Priya, our parents, to my brothers 
and to my sisters. Without their continued support I could not have completed this.
iii
ACKNOWLEDGEMENTS
I would like to acknowledge the inspirational support given from the lecturers and 
staff of Department of Electronic and Telecommunication Engineering, University of 
Moratuwa, Sri Lanka.
I wish to acknowledge with sincere gratitude, my supervisor Dr. Ajith Pasqual for his 
advice and guidance during this study and writing of this report.
I would not hesitate to acknowledge the enormous support given by industry 
personal, to gather statistics related to telecommunication industry not limited to Sri 
Lanka but also in other countries.
Also I would like to thank my friends, batch mates and co-workers at my office for 
their support and encouragement.
I thank my wife Priya for her support and encouragement. I could not have 
completed this without her assistance, tolerance and enthusiasm.
iv
TABLE OF CONTENTS
Declaration of the candidate & Supervisor
Abstract
Dedication
Acknowledgements
Table of Contents
List of Figures
List of Tables
List of abbreviations
1 Introduction
1.1 Motives for the Project Work
1.2 Synchronization of Digital Telecommunications Networks
1.2.1 Frequency Synchronization
1.2.2 Clock Synchronization
1.2.3 Synchronization Errors
1.3 Problem Statement
1.4 Technical Approach
1.5 Main Contributions of the Dissertation
1.6 Outline
2 Synchronization of networks
2.1 Network Synchronization Strategies 
2.1.1 Clocking Strategies
2.2 Synchronization Network Standard Architectures for Clocks
2.3 Methods of Synchronization
v
102.4 Synchronization Network Protection
113 Synchronization in Packet Switching Networks
123.1 Packet Backhaul Domains
123.1.1 Packet Network Timing (PNT) Domain
123.1.2 Circuit Emulation Services (CES) Domain
133.2 Differential Clock Recovery (DCR)
Advantages of Differential Clock Recovery (DCR) 143.2.1
3.3 Adaptive Clock Recovery (ACR)
3.3.1 Advantages of Adaptive Clock Recovery (ACR)
14
14
3.4 Combination Clock Recovery (CCR)
3.5 In-Band and Out-of-Band Synchronization over Packet Network
14
15
3.5.1 In-Band Synchronization over Packet 15
3.5.2 Out-of-Band Synchronization over Packet 
3.6 Review on Synchronous Ethernet (SyncE) 
3.6.1 Clock and Data Path in SyncE
15
15
16
3.6.2 Network Clock and Service Clock 17
3.7 Review on IEEE 1588v2 17
3.7.1 PTP Slave Clock Acquisition and Locking Process 
4 Timing over Packet Network
19
21
4.1 ITU-T Recommendations in Synchronization 21
4.2 Implementation Considerations
4.3 Implementing Functionalities
22
23
4.3.1 Implementing SyncE Functionalities
4.3.2 Implementing PTP Functionalities 
4.4 Suitability of Packet Networks
4.4.1 Suitability of Packet Networks for SyncE
24
24
25
25
vi
264.4.2 Suitability of Packet Networks for PTP
285 Guide for Technology Selection
29Backhaul Scenarios5.1
295.1.1 TDM Backhaul
30IP Overlay on TDM Backhaul5.1.2
315.1.3 Hybrid Backhaul
5.1.4 Packet Backhaul 31
5.2 Number of Hops for the Backhaul 32
5.3 IP RAN Deployment 32
5.4 Decision Matrix 36
6 Conclusions and Recommendations 38
6.1 Conclusions 38
6.2 Recommendations 39
6.2.1 Grandmaster Clock 40
6.2.2 Recommendations for SyncE Quality and Priority 42
6.2.3 Recommendations for IEEE 1588v2 43
6.2.4 Network Requirement 
Microwave Network Requirement 
Performance Management
44
6.2.5 44
6.2.6 46
6.3 Research Contribution and Future Work 46
Reference List 48
vii
LIST OF FIGURES
3Figure 1.1: Timing signals a) Sinusoidal signal b) Step signal
Figure 1.2: Jitter affecting to a digital signal..........................
Figure 2.1: Clock distribution strategies a) Distributed clock b) Master-slave clock..8
Figure 3.1: Clock and data path in SyncE....................................................
Figure 3.2: SyncE network element and clock distribution.........................
Figure 3.3: IEEE 1588v2 deployment.........................................................
Figure 3.4: General principle of packet-based timing methods...................
Figure 3.5: Illustration of PTP slave clock acquisition and locking process
Figure 4.1: Technology Status...................................................................
Figure 5.1: Synchronization from El.........................................................
Figure 5.2: Synchronization over TDM Backhaul......................................
Figure 5.3: IP Overlay on TDM Backhaul..................................................
Figure 5.4: Packet transport network with El Sync out..............................
Figure 5.5: Hybrid Backhaul.......................................................................
Figure 5.6: Packet transport network with Ethernet Sync out.....................
Figure 5.7: Packet Backhaul.......................................................................
Figure 5.8: Example of IEEE 1588v2 GM locations..................................
Figure 5.9: Boundary Clock in Network for TDD applications...................
Figure 6.1: High level Clocking Architecture.............................................
Figure 6.2: Primary Reference Clock..........................................................
Figure 6.3: Leased Bandwidth to Complete Ring.......................................
Figure 6.4: SyncE Priority in Interfaces.....................................................
Figure 6.5: Priority and Queuing in Core Network.....................................
Figure 6.6: Microwave Network Priority for Clock....................................
Figure 6.7: Priority and Queuing in Microwave Network...........................
5
16
17
18
19
19
21
29
30
30
31
31
32
32
33
36
39
40
41
43
44
45
45
viii
LIST OF TABLES
11Table 3.1: Air interface synchronization requirement.......................
Table 3.2: PTP slave clock acquisition and locking process.............
Table 5.1: IEEE 1588v2 / SyncE Comparison..................................
Table 5.2: Traffic Class and Classification.......................................
Table 5.3: Synchronization selection matrix with TDM existence.... 
Table 5.4: Synchronization selection matrix after fuII-IP conversion
19
28
35
36
37
ix
LIST OF ABBREVIATIONS
Abbreviation Description
Adaptive Clock Recovery
American National Standards Institute
Boundary Clock
Base Station Controller
Base Transceiver Station
Constant Bit Rate
Combination Clock Recovery
Circuit Emulation Services
Circuit Emulation Services over Packet
Class of Service
Cell Site Router
Differential Clock Recovery
Domain Name Service
DiffServ Code Point
Ethernet Equipment Clock
Edge Masters
European Telecommunications Standards Institute
Ethernet Virtual Circuit
Frequency Locked Loop
File Transfer Protocol
Grand Master
GSM Media Gateways
Global Navigation Satellite System
Global Positioning System
Hyper Text Transfer Protocol
Internet Engineering Task Force
Internet Message Access Protocol
Internet Protocol
Internet Protocol Television
ACR
ANSI
BC
BSC
BTS
CBR
CCR
CES
CESoP
CoS
CSR
DCR
DNS
DSCP
EEC
EM
ETSI
EVC
FLL
FTP
GM
GMGW
GNSS
GPS
HTTP
IETF
IMAP
IP
IPTV
x
International Telecommunication Union
Inter Work Function
Label Switch Path
Metro Ethernet
Metro Ethernet Forum
Multi Protocol Label Switching
Mean Time Interval Error
Network Timing Protocol
Ordinary Clock
Packet Delay Variation
Per Hop Behavior
Phase Locked Loop
Packet Network Timing
Primary Reference Clocks
Packet Switching Network
Quality Level
Quality of Service
Radio Network Controller
Synchronous Digital Hierarchy
Signaling Transport
Session Initiation Protocol
Simple Mail Transfer Protocol
Synchronous Optical Network
Synchronization Status Messages
Synchronization Supply Units
Synchronous Ethernet
Time Division Multiplexing
Type of Service
User Datagram Protocol
Unit Interval
Virtual Local Area Network
ITU-T
IWF
LSP
ME
MEF
MPLS
MTIE
NTP
OC
PDV
PHB
PLL
PNT
PRC
PSN
QL
QoS
RNC
SDH
SIGTRAN
SIP
SMTP
SONET
SSM
SSU
SyncE
TDM
ToS
UDP
UI
VLAN
xi
VLL Virtual Leased Line
VOD Video on Demand
xii