Phase/time alignment between base stations requirement can ..... The notion of
frequency synchronization (or syntonization) is making the time-bases “equal” ...
Frequency and Time Synchronization In Packet Based Networks Peter Gaspar, Consulting System Engineer
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• Synchronization Problem Statement • Overview of the Standardization Works • Frequency Transfer: techniques and deployment Synchronous Ethernet Adaptive Clock Recovery • Time Synchronization Two-Way Transfer Time Protocols • Overview of IEEE Std 1588-2008 for Telecom • Summary
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Problem Statement What and Why Do We Care About?
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Why and How are Packet Switched Networks Involved? • Transition from TDM to Ethernet networks. Access
Subscriber Mobile TV
• Connect consumers requiring Frequency
and/or Time (F&T) synchronization.
TDM / ATM
• PSN is built with network elements that
DVB-T/H 3GPP/2
May have to support F&T distribution
WiMAX
May be consumers of F&T
Mobile user
Aggregation
Ethernet Femto-cell
DSLAM
P
xDSL OLT
Enterprise
M-CMTS
P
P
PE
Hub & Spoke or Ring
MS A
P
MSE
Internet
Mesh
Content Network
DOCSIS
VoD TV Portal
Peer ISP
P
PE
PE
xPON Residential SoHO
Backbone
TDM / ATM
Monitoring Billing Subscriber Database
SI P
Identity Address Policy Mgmt Definition
Service Exchange
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• Single domain vs. multiple domains
Access
Subscriber
Internet is a multi-domain network. Mobile TV
TDM / ATM
Wholesale Ethernet virtual link
• Frequency and time could use different
DVB-T/H 3GPP/2
distribution methods.
WiMAX
• Operators may provide synchronization services
to their customers.
Mobile user
Aggregation
Ethernet
Backbone
Peer ISP
TDM / ATM
Femto-cell
DSLAM P
xDSL OLT
Enterprise
DOCSIS
© 2010 Cisco and/or its affiliates. All rights reserved.
P
PE
Hub & Spoke or Ring
MSA M-CMTS
P
PE
PE
xPON Residential SoHO
P
P
MSE
Mesh
Content Network VoD
TV
Internet
SIP
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• Frequency TDM interoperability and Co-existence: Circuit Emulation, TDM, MSAN (MGW) Access: Wireless Base Stations, PON, DSL • Time and Phase alignment Wireless Base Stations SLA and Performance Measurements
BS PON DSL SLA © 2010 Cisco and/or its affiliates. All rights reserved.
: Base Station : Passive Optical Network : Digital Subscriber Line : Service Level Agreement Cisco Confidential
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External Integrated Time and Frequency Server
• Inter-CO/LAN (WAN) • Intra-CO, LAN • Intra-node, -platform © 2010 Cisco and/or its affiliates. All rights reserved.
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The Leading Requirements Application TDM support (e.g. CES, SDH transformation), Access
Frequency PRC-traceability, jitter & wander limitations ITU-T G.8261/G.823/G.824/G.825
GSM, WCDMA and LTE FDD UMTS TDD Mobile Base Stations
TD-SCDMA CDMA2K
Phase Alignment Time Synchronization
N/A (except for MBMS and SFN) Frequency assignment (fractional frequency accuracy) shall be better than • ± 50ppb (macrocells) • ± 100ppb (micro- & pico-cells) • ± 250ppb (femtocells)
Phase alignment between base stations must be < ±2.5µs Phase alignment between base stations must be < ±3µs Time alignment error should be less than 3 µs and shall be less than 10 µs Phase alignment between base stations from ±0.5µs to ±50µs (service degradation)
LTE TDD WiMAX Mobile
Shall be better than ± 15 ppb
Phase alignment between base stations must be < ±1µs
DVB-S/H/T2 SFN
TBD
Cell synchronization accuracy for SFN support must be < ± 3µs
MB SFN Service
Phase/time alignment between base stations requirement can vary but in order of µs
One-way delay and jitter Performance Measurement
To improve precision 1) Server UTC • Node by node: BC slave function is critical
Ordinary Slave
Ordinary Master
Recovered Clock BC
Boundary Clock © 2010 Cisco and/or its affiliates. All rights reserved.
Ref. Clock
BC
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• TC calculates Residence Time (forward / reverse intra node
delays). • TC are supposed to be transparent but: One-step clock issue
Ordinary Slave
Ordinary Master
Recovered Clock TC
Transparent Clock © 2010 Cisco and/or its affiliates. All rights reserved.
Ref. Clock
TC
Transparent Clock Cisco Confidential
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• If IEEE 1588-2008 is not planned node to node, with every
node IEEE 1588 aware and in unique domain…
• Multiple interface types IEEE 802.3, ITU-T G.709, … • Multiple interface frequencies 10GE, 100GE, STM64, STM192… • Multiple encapsulations Ethernet, IP MPLS, MPLS-TP, PBB-TE…
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Ordinary Slave Recovered Clock
Ordinary Master TC
TC
Wholesale
BC
Ref. Clock
BC
Boundary Clock
• Who owns the master? • Who owns the slaves? • Who owns the intermediate nodes? © 2010 Cisco and/or its affiliates. All rights reserved.
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• How to guarantee the recovered clock quality?
Objective: accuracy and stability from reference Slave/ Client Recovered Clock
?
?
TC
Master/ Server
Ref. Clock
PSN BC
?
? ?
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• IEEE Std 1588-2008 is actually a “toolbox” !
What does “support of IEEE 1588” really mean ? • IEEE Std 1588 itself is not sufficient for telecom operator operations. Node characterization, modeling, performance, metrics… • For phase & time support, it is expected any telecom standardization
would take time.
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Summary
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• Timing is a new service many networks shall have to support. • Different solutions are necessary to cover disparate requirements,
network designs and conditions. Physical layer solutions required to upgrade routers and switches. Packet-based solutions are more flexible but less deterministic. • Whatever the timing protocol, it must deal with the same network
constraints. • Each network is different • Synchronization Experts are welcome to enter the packet based
networks and assist with the designs
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Thank you.
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