Dominik Schneuwly examines how to evolve from legacy to next-generation network synchronization

1. Smooth Evolution Path from
Legacy to NGN Synchronization
Dominik Schneuwly, ITSF 2014

2. © 2014 ADVA Optical Networking. All rights reserved.2
Outline
• Drivers of the evolution
• Dimensions of the evolution
• Evolution starting points
• Evolution phases and end points
• Evolution path examples
• Conclusions

3. © 2014 ADVA Optical Networking. All rights reserved.3
Driver of the evolution
• Network technology evolution from TDM to packet-switched
networks, and from fixed to fixed & mobile end sytems
• Synchronization in the past:
• Driver: TDM switching (telephony) and transmission (SDH)
• Reasons: limit under- and overflowing of frame buffers,
allow crossconnecting (SDH)
• Requirements: frequency, accuracy 1·10-11 (relative freq. acc.)
• Synchronization at present and in the future:
• Driver: mobile base stations, e.g. 2G BTS, 3G Node B, 4G eNB
• Reasons: successful call handover
efficient use of sparse spectrum & channel capacity
etc.
• Requirements: frequency (1.6E-8) and phase (1.5 μs ⇾ hundreds ns)

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Dimensions of the evolution
• Change in synchronization needs
• Old: frequency for the entire network (1E-11)
• New: frequency (1.6E-8) and phase (1.5 μs ⇾ hundreds ns) for the
network edge
• Change in network technology
• Old: TDM networks (PDH, SDH)
• New: packet-switched networks
• Ethernet, Synchronous Ethernet (SyncE)
• IP, IP/MPLS
• Etc.
• Change in synchronization technology
• Old: SDH/SONET, E1/T1 over PDH
• New: SyncE, PTP (IEEE 1588 v2)
Synchronization
technology
Synchronization
needs
Network
context

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Once more: frequency, phase and time-of-day
t
t
Clock signal of system A
Clock signal of system B ! !!
t
t
Time signal of system A
Time signal of system B
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08:34:56
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08:34:57
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08:34:55
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08:34:55
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08:34:56
14/01/00
08:34:57
System A System B
t
t
Clock signal of system A
Clock signal of system B
TA = 1 / fA
TB = 1 / fB
fA = fB• Frequency synchronization
• Phase synchronization
• Time-of-Day synchronization

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Application Radio Interface Backhaul
Frequency Phase Frequency Phase
CDMA 2000 ±50ppb ±3 to 10µs GPS GPS
GSM ±50ppb n/a ±16ppb n/a
WCDMA ±50ppb n/a ±16ppb n/a
LTE (FDD) ±50ppb n/a ±16ppb n/a
LTE (TDD) ±50ppb ±1.5µs ±16ppb ±1.1µs
LTE-A MBMS ±50ppb ±1 to 5µs ±16ppb
±1µs
(G.8271)
LTE-A CoMP
LTE-A CoMP JT
±50ppb
±1 to 5µs
± 0.5µs
±16ppb
±1.1µs
< 0.5µs (?)
LTE-A eICIC ±50ppb ±1 to 3µs ±16ppb ±1.1µs
Frequency and phase synch. requirements
MBMS: Multimedia Broadcast Multicast Services CoMP: Coordinated
Multipoint
eICIC: enhanced Inter-Cell Interference Coordination JT: Joint Transmission

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Starting point 1: central PRC
PRC
SDH
SSU
SSU
SSU
SSU
SSU
• Frequency synchronization
with accuracy = 1E-11
• Generation: central PRC,
typically atomic Cesium
clock
• Distribution: SDH, physical
layer; sometimes E1/T1 in
«last mile»

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Starting point 2: distributed PRCs
SDH
Subnetwork
PRC
SDH
Subnetwork
PRC
SDH
Subnetwork
PRC
• Frequency synchronization with accuracy = 1E-11
• Generation: distributed PRCs, typically GNSS receivers
• Distribution: SDH, physical layer; sometimes E1/T1 in «last mile»

9. © 2014 ADVA Optical Networking. All rights reserved.9
Transition phases
• Main transition phases:
• A: Frequency over TDM network
• SDH/SONET
• B: Frequency over packet network
• SyncE
• PTP / No Timing Support (G.8265.1)
• C: Phase over packet network
• PTP / Full Timing Support (G.8275.1) with SyncE
• PTP / Full Timing Support (G.8275.1) without SyncE (ITU-T: «ffs»)
• PTP / Assisted Partial Timing Support (G.8275.2)
A B C
(less common)

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Transition A → B
B / A SDH & PDH
SyncE X
G.8265.1 X
Transition B → C
C / B SyncE G.8265.1
G.8275.1 X X
G.8275.2 X X
Many evolution scenarios
Transitions A → B → C:
SDH & PDH → SyncE → G.8275.1
SDH & PDH → SyncE → G.8275.2
SDH & PDH → G.8265.1 → G.8275.1
SDH & PDH → G.8265.1 → G.8275.2

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There are more evolution scenarios than that!
• Already mentioned: Starting point (SDH & PDH) can be with
centralized or with decentralized PRCs
• There are multiple mobile systems (2G, 3G, 4G); evolution
scenarios may be different for each of them
• Multiple network ownerships (mobile operator, transport provider,
etc.)
• Networks with equiment from multiple vendors: different
equipment roadmaps
• Some operators use CES/PWE for their 2G BTS (PDH over packet
network)
• And we haven’t mentioned WDM systems in conjunction with
phase synchronization …
• Etc., etc.

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Evolution example 1a: SDH & PDH → SyncE → G.8275.1
Leverage existing PRC and SSUs
SSU
PRC
SDH
or
SyncE
SyncE
SSU
PRC
SDH
SDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE

13. © 2014 ADVA Optical Networking. All rights reserved.13
Evolution example 1a: SDH & PDH → SyncE → G.8275.1
Leverage existing PRC and SSUs, just add cards to SSUs for phase
SSU
PRC
SDH
SyncE
SSU
PRC
SDH
SDH & PDH
SSU
SyncE
GNSS
card
T-GM
card
GNSS
Physicallayerbased
Packetbased(PTP)
G.8275.1
Deploy
Boundary Clocks
Add cards
Upgrade to
PTP Slave
Upgrade to
SyncE
Core

14. © 2014 ADVA Optical Networking. All rights reserved.14
Evolution example 1b: keep PRC for phase holdover
Leverage existing PRC and SSUs, just add cards to SSUs for phase
SSU
PRC
SDH
or
SyncE
SyncE
SSU
PRC
SDH
SDH & PDH
SSU
SyncE
GNSS
card
T-GM
card
GNSS
Physicallayerbased
Packetbased(PTP)
G.8275.1
Deploy
Boundary Clocks
Add cards
Upgrade to
PTP Slave
Upgrade to
SyncE
PRC
SDH
or
SyncE
For Holdover:
frequency
holds phase &
time

15. © 2014 ADVA Optical Networking. All rights reserved.15
Evolution example 1c: starting with decentralized PRCs
Leverage existing GNSS/SSUs, just add T-GM card to SSUs for phase
SyncESDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE
GNSS
card
GNSS
SSU
GNSS
card
GNSS
SSU
Local PRC Local PRC

16. © 2014 ADVA Optical Networking. All rights reserved.16
Evolution example 1c: starting with decentralized PRCs
Leverage existing GNSS/SSUs, just add T-GM card to SSUs for phase
SyncESDH & PDH
SSU
SyncE
GNSS
card
T-GM
card
GNSS
Physicallayerbased
Packetbased(PTP)
G.8275.1
Deploy
Boundary Clocks
Add card
Upgrade to
PTP Slave
Upgrade to
SyncE
GNSS
card
GNSS
SSU
GNSS
card
GNSS
SSU
Local PRC Local PRC Local PRTC

17. © 2014 ADVA Optical Networking. All rights reserved.17
Evolution example 2a: SDH & PDH → SyncE → G.8275.2
Add cards to SSUs and add small APTS units for phase
SSU
PRC
SDH
or
SyncE
SyncE
SSU
PRC
SDH
SDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE

18. © 2014 ADVA Optical Networking. All rights reserved.18
Evolution example 2a: SDH & PDH → SyncE → G.8275.2
Add cards to SSUs and add small APTS units for phase
SSU
PRC
SDH
or
SyncE
SyncE
SSU
PRC
SDH
SDH & PDH
SSU
SyncE
GNSS
card
T-GM
card
GNSS
Physicallayerbased
Packetbased(PTP)
G.8275.2
Add cards
Upgrade to
PTP Slave
Upgrade to
SyncE
APTS
GNSS
G.8275.2
Add APTS unit
First
Aggregation
node

19. © 2014 ADVA Optical Networking. All rights reserved.19
Evolution example 3a: SDH & PDH → G.8265.1 → G.8275.1
Leverage existing PRC and SSUs, just add cards to SSUs for phase
PRC
SDH
or
Synce
Carrier
Ethernet
SSU
PRC
SDH
SDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE
G.8265.1
T-GM
card
Add card
SSU

20. © 2014 ADVA Optical Networking. All rights reserved.20
Evolution example 3a: SDH & PDH → G.8265.1 → G.8275.1
Leverage existing PRC and SSUs, just add cards to SSUs for phase
PRC
SDH
or
Synce
Carrier
Ethernet
SSU
PRC
SDH
SDH & PDH
SSU
Carrier
Ethernet
GNSS
card
T-GM
card
GNSS
Physicallayerbased
Packetbased(PTP)
Deploy
Boundary Clocks
Add card
Upgrade to
PTP Slave
Upgrade to
SyncE
Core
G.8265.1
T-GM
card
Add card
SSU
G.8275.1

21. © 2014 ADVA Optical Networking. All rights reserved.21
Evolution example 4a: SDH & PDH → G.8265.1 → G.8275.2
Add cards to SSUs and add small APTS units for phase
PRC
SDH
or
SyncE
Carrier
Ethernet
SSU
PRC
SDH
SDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE
T-GM
card
SSU
Add card
G.8265.1

22. © 2014 ADVA Optical Networking. All rights reserved.22
Evolution example 4a: SDH & PDH → G.8265.1 → G.8275.2
Add cards to SSUs and add small APTS units for phase
PRC
SDH
or
SyncE
Carrier
Ethernet
SSU
PRC
SDH
SDH & PDH
Physicallayerbased
Packetbased(PTP)
Upgrade to
SyncE
T-GM
card
SSU
SSU
Carrier
Ethernet
GNSS
card
T-GM
card
GNSS
G.8275.2
Add card
Upgrade to
PTP Slave
APTS
GNSS
G.8275.2
Add APTS unit
First
Aggregation
node
Add card
G.8265.1

23. © 2014 ADVA Optical Networking. All rights reserved.23
Conclusions
• Evolution is driven by changes in synchronization needs, network
context and synchronization technologies
• There are many possible evolution scenarios
• Leveraging existing SSUs and PRCs is possible with many evolution
scenarios
• Within these scenarios, evolution requires addition on T-GM cards
in SSUS, and possibly addition of small APTS units
• Chosen evolution path has important impact on CAPEX
• Optimal planning of the evolution path is a must

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Thank you
schneuwly@oscilloquartz.com