synchronization over packet networks2

8/14/2019 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



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



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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