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8/8/2019 70 Packet Synch
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Mobile Synchronisation
All Rights Reserved © Alcatel-Lucent 2008
Rolf Sperber (Material from Dave Sargent)
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Why Synchronization over Packet Networks
Network Convergence
Triple Play
QoS and OAM for VoIP
QoS and OAM for VoD
QoS and OAM for Video Distribution
No Synchronization Requirements
Business Applications going Packet
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QoS, OAM and Synchronization for Circuit Emulation Services QoS and OAM for L2 VPNs
QoS and OAM for L3 VPNs
Mobile Applications going Packet
QoS, OAM and Synchronization for GSM access over Packet QoS, OAM and Synchronization for UMTS access over Packet
QoS, OAM and Synchronization for LTE access
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Trend in large carrier’s network design: network convergence
Overall architecture
BRASVoice
GWDSLAM
MSAN
EthNT
3PLAY CPE
FTTH
VDSL
Edge CoreAggregationAccess
MSC
Target architecture
Single packet aggregation / core network on top of OTN
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(e)NODE B
BTS RNC
BSC Voice
GW
SSU T PRC
synchronization
SSU L
The synchronization network today relies on the omnipresent SDH synchronicity
Which are the requirements for the packet / OTN network to support nation-widesynchronization when SDH has gone?
Do all future nodes need to be synchronous?
Do all connections need to be synchronous?
Are protocol based solution the panacea?
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Key Requirements of Synchronization
Key limits for sync that we look at are defined in G.813 and G.823
These specify the timing accuracies and stabilities required for delivery of both data and Synchronisation references over SDH networks
Traffic Interface network wander limit – allows sizing of slip buffers toensure no data loss
Synchronisation Interface wander limit – ensure the signal is stableenough to allow a clock to lock to it and propagate the timing chain
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Mobile basestations use the E1 interfaces from the SDH networks assources of a 2.048 MHz reference
Reference must be stable enough to allow them to meet radio frequencyaccuracies to ± 50 ppb (10-9)
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TDM
Network
TDM
Network
Reference
Clock
Synchronization in Heterogeneous Environments
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PacketNetwork
Packet
Switch
CES
Packet
Switch
CES
TDM
Switch
TDM
Switch
E1 TDM E1 TDM
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Synchronisation Distribution
G.811 – Stratum 1 PRC, Caesium or GPS
G.812 – Stratum 2 SSU-T, Rubidium, HQ-OXCO
G.813 – Stratum 3 SSU-L
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Main goal of SynchronisationDistribution is to ensure that acommon reference frequency isused by all transmitters
Can originate for a single
oscillator (PRC) Can be distributed by GPS
If transmitters are independent,traffic over/underruns can occur
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Timing Measurements
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Even if all the devices are traceable back to the same PRC, their references may notbe stable
Over the short term observation the frequency may drift
Comparing the reference signal at a device to the PRC output is the technique usedto measure the timing stability and accuracy.
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Time Interval Error (TIE)
Fundamental metric for comparing clocks
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Carrier Frequency Accuracy for Handoff Control
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Handset expects to see the carrier at F2
If F2 > 50ppb from nominal, handset wont find it and call drops.
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Synchronization Options
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Ways to Synchronize
Overlay Synchronization Network
TDM network in parallel exists
Interim Solution
Distributed Reference Clock Solution
PRC traceable via GPS
Future proof solution
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ranspor o m n n orma on v a pac e e wor
Packet based solutions
PHY based solutions
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Reference
Clock
TDM Network
Overlay Network for Synchronization
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Packet NetworkAsynchronous
Packet
SwitchCES
Packet
Switch
CES
TDM
Switch
E1 TDM
SynchronizationPurposesTDM
Switch
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Distributed PRC for Synchronization (GPS)
Reference
Clock
TDM Network
for Classical Time
Distribution
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Packet NetworkAsynchronous
Packet
Switch
CES
Packet
Switch
CES
TDM
Switch
E1 TDM
TDM
Switch
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Primar
Slave
Hierarchical Clock Distribution
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SwitchCES
TDM
SwitchReferenceClock
Packet
Switch SwitchCES
TDM
Switch
TDM
Switch Application
Master
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Adaptive Clock Recovery
General:
In adaptive timing or adaptive clock recovery (ACR) the reference clockinformation is encapsulated and decapsulated at the packet edge nodesthat provide interworking function between TDM and packet domains
Protocols
Network Time Protocol (NTP) RFC 1305
Lack of precision
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Proprietary Implementations Do not require NTP compliant intermediate nodes
Number of nodes between timing source and destination matters
Precision Time Protocol (PTP) according to IEEE 1588v2
Normalization with respect to packet size between timing packets
Not all intermediate clocks need to support 1588v2
Support of transparent clock and boundary clock
Support of timestamps for ToD (important in LTE context)
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TDM
Network
TDM
Switch
TDM
Switch
Reference
Clock
Adaptive Clock Recovery
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PacketNetwork
SwitchCES SwitchCESE1 TDM E1 TDM
Clock Information
Transport
Interworking
Function
Interworking
Function
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Differential Clock Recovery
General:
In differential clock recovery (DCR) both edge elements performing theinterworking function have to have access to a common reference clock
Specifics: Frequency not recovered from incoming packets
Normalization with respect to propagation possibel, not necessary
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Less stringent requirements for intermediate nodes
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TDM
Network
TDM
Network
TDM
Switch
TDM
Switch
Reference
Clock
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PacketNetwork
SwitchCES SwitchCESE1 TDM E1 TDM
Clock Information
Transport
Interworking
Function
Interworking
Function
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Synchronous Ethernet (G.8261)
General:
PHY based protocol
Specifics
Independent of network load
No ToD
Here we have to insert timestamps, so a combination of both packet based andpacket independent is advisable.
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Every Element in the chain has to comply to G.8261 It is however possible to have non compliant nodes inbetween if there is an
interworking function between Synch Ethernet and ACR
Synchronous Ethernet complies with the stringent precisionrequirements as defined for SDH
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Packet
Switch
CES
Packet
Switch
Query if neighbour
is G.8261 compliant
Packet
Switch
CES
Packet
Switch
Standard Packet
Forwarding
Synchronous Ethernet G.8261
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nswer s no
Packet
Switch
CES
Packet
Switch
Query if neighbour
is G.8261 compliant
Answer is yes
Packet
Switch
CES
Packet
Switch
Synchronous
Ethernet Forwarding
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Network Sync Options
External (e.g. GPS)
2.048 MHz G.703 section 13
5 or 10 MHz sine wave (TTL level at 50 ohm)
Node B
Node B
Sync
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Primary
ReferenceClock
Line Timing
Synchronize to E1 or SDH
Node B
PDHNode B
Node B
Sync
Node B
Sync
7705 SARAggregation
Node7710/7750 SR
Transport Node at MTSO
7705 SARAggregation
Node 7710/7750 SRTransport Node at MTSO
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Network Sync Options
Adaptive Clock Recovery
ACR algorithm recovers clock based on constant rate of packet arrival
Node B
Eth7705 SAR
Node B
Node B
Packet flow at constant
rateACR
PrimaryReference
Clock
Sync
7710/7750 SR
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Local Stratum 3 Clock/holdover
In case all references fail
Node B
Node B
Node B
Node
Loca
lOSC
Transport Node at MTSO
7705 SARAggregation
Node
7710/7750 SRTransport Node at MTSO
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Evolving Network Sync Options
IEEE 1588v2 Slave
Sync (1588 messageexchange)
Ethernet
Node B
Node B
Node B
7705 SARAggregation
Node
7710/7750 SRTransport Node at MTSO
PrimaryReference
Clock
Sync
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.
Sync
Ethernet
Node B
Node B
Node B
7705 SARAggregation
Node
7710/7750 SRTransport Node at MTSO
PrimaryReference
Clock
Sync
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Testing 8261
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G.8261 test specifics
TestEquipment
TestEquipment
PacketDelay
Variation
Jitter,Wander,
Frequencyaccuracy
1
Reference Timing Signal (PRC)
* The ReferenceTiming Signal(PRC) is used torepresent theTDM serviceclock
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TDMsignal
CE(TDM
trafficgenerator) IWFTDMsignal
IWF
(DUT)
Referencepoint 2
Referencepoint 3
GE GE
GE = 1 Gbps Ethernet
FE = 100 Mbps Ethernet
GE FE or GEGE
Ethernet Switches
N = 10
. . .
Flow of interest
Disturbance load according to traffic models
GEGE GEGE
Traffic Generator
. . .
. . .Reference
point 1
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SyncE in 7750 / 7705
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Lab testing for 7750/7705 in SyncE Clock Recovery (24- node network)
SyncE
SAR-8#1 7750 SR
#2
SyncESyncE
SAR-F#18
SyncE
SAR-F#19
SAR-F#20
2.048MHz2.048MHz
Monitor #1
E1
Monitor #2
7750 SR #3
SyncE
SAR-8#4
SyncE
. . .
24 Nodes
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Timing over Synchronous Ethernet performance test
Test over a large network:
- Transport over 24 nodes
Test performance over long duration
- For 10 hours