Packet Synchronization over Carrier Ethernet Networks for MBH.pdf
Synchronization Over Packet Networks2
Transcript of Synchronization Over Packet Networks2
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Sync hron iza t ion over Pac k et Net w ork s
Jeremy Lewis
Product Line Marketing Manager
Zarlink Semiconductor
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Agenda
Why Synchronization over PSN
Applicable Standards
In-Band & Out-of-Band
Adaptive Clock Recovery
Differential Clock Recovery
Combination Solution
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Why Sync hronizat ion Over PSN
What is this technology?
Encode server clock frequency/phase information
Transmit server clock information over the PSN
Recover an accurate clock at the client nodes
Benefits of Synchronization over PSN
Replaces the need for GPS receivers at client nodes
Replaces the need for synchronization cables betweennodes
Replaces the need for high stability oscillators
Eliminates the need for routine calibration of highstability oscillators
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St andards for Sync hronizat ion
E1 Standards (2.048 Mbps)
Traffic interface
(G.823, Table 2)
18s over 1000s
T1 Standards (1.544 Mbps)
Traffic interface
(T1.403, section 6.3.1.2)
8.4s over 900s
18s over 24 hours
Max. end-to-end wander (traffic interface) 18 sPSN induced wander < 18 s
CustomerPremises
CentralOffice
RemoteTerminal
IWFIWFT1/E1
PRS
PSTNTDM
EquipmentPSNT1/E1
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St andards for Sync hronizat ion
E1 Standards (2.048 Mbps)
PDH synchronization
interface (G.823 - Table
12)
2s over 2000s
5.33s over 100,000s
T1 Standards (1.544 Mbps)
Reference interface
(T1.101, section 7.2.1)
1 s over 2000s
2s over 100,000s
CentralOffice
RemoteTerminal
IWFIWFT1/E1
Max. end-to-end wander (synchronization interface) 2 sPSN induced wander < 2 s
PRS
PSTN
Network
TDMEquipmentPSN
T1/E1
PBx
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In-Band & Out -of-Band
In-Band Synchronization over Packet
Uses information included in the standard CESoP datastream
Each T1/E1 has its own associated clock No timing traffic overhead
Data and timing are closely coupled
Out-of-Band Synchronization over Packet
Uses dedicated timing packets
Examples: NTP, IEEE 1588
Adds some timing traffic overhead
Can be always on
Configurable to network conditions
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In-Band Tim ing Rec overy
Timing recovery for CESoPSN/TDM-over-IP
Clock & data use the same packet connection
Data Payload
Clock Header
CustomerPremises
CustomerPremises or
Central Office
Carrier PSNCarrier PSNCESoP
IWF
CESoP
IWF
EncodedClock
EncodedData
Single T1Clock and Data
Multiple Streams possible
Recovered T1Clock and Data
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Out -of-Band Tim ing Rec overy
Timing recovery for all applications
Clock & data use separate packet connections
GSM / UMTSBasestation
PrimarySource
BITSSSU
SecondarySource
BITSSSU
Servers
V.90 MODEM
TDM PBX
VoIPGateway
Clients
BaseStation
BaseStation
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In-Band Vs Out -Of-Band
In-band clock recovery advantages
No bandwidth overhead
High packet rate, equal to the CBR traffic rate
Uses already defined standards (e.g. CESoP)
Out-of-band clock recovery advantages
Separation of clock recovery from the data allows forgreater flexibility (e.g. always on operation)
Configurable for network conditions (e.g. packet rate1,000pps)
Far less susceptible to poor network conditions
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Adapt ive Cloc k Rec overy
Reference clock, only available at the server Service is frequency & phase encoded
Accurate time stamp applied & packets sent via in-band or out-of-band
Filtering of the of the arriving packets provides Service
at the Clientnode
CustomerPremises
CentralOffice
Server Node TDMEquipment
Client NodeTDMEquipment
Filter
Queue
Service Service
T1/E1T1/E1
ClockEncode
Carrier PSN
TimeStamp
TDM toPacket
Packetto TDM
In-Band
Out-of-Band
PrimaryReference
Source
fReference
TimeStamp
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Adapt ive Cloc k Rec overy
No common reference required
Good jitter and wander performance is achievable
~2S MTIE
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Dif ferent ia l Cloc k Rec overy
Reference clock available at server & client
Only the difference between Service & Reference is transferred acrossthe PSN
CustomerPremises
CentralOffice
Server Node TDMEquipment
Client NodeTDMEquipment
Add
Queue
ServiceService
T1/E1T1/E1
TimingDifference
Carrier PSN
TimeStamp
TDM toPacket
Packetto TDM
In-Band
Out-of-Band
PrimaryReference
Source
fReferencefServiceis asynchronous tofReference
TimeStamp
Difference
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Dif ferent ia l Cloc k Rec overy
Good jitter and wander performance
Largely unaffected by network delay, delay variationand packet loss
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Com binat ion Cloc k Rec overy
Reference clock, only available at the server Service is encoded using adaptive technique & sent separate to
CESoP traffic
Only the difference between the T1/E1 clocks & Service transferred
across the PSNCustomerPremises
CentralOffice
Server Node TDMEquipment
Client NodeTDMEquipment
Add
Queue
ServiceService
T1/E1 T1/E1
TimingDifference
Carrier PSN
TimeStamp
TDM toPacket
Packetto TDM
In-Band
Out-of-Band
PrimaryReference
Source
fReference
Time
Stamp
Filter
Clock
Encode
TimeStamp
Difference
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K ey Per form anc e Fac t ors
PDV
The nature of the PDV needs to be understood
Network loading
Average network node loadingPacket Rate
Increased rate of timing packet generally increasesperformance
Complexity of the network
Number of nodes, L2/L3
Drift Rate of the local oscillator
OCXO, TCXO
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Fur t her Per form anc e Fac t ors
Network disturbances
Packet loss
Network congestion/modulation/bursts
Network outage Routing changes
Night & day low frequency effects
Network models/characterization Performance models
Test bench
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