Double Migration

of Packet Clocks

Kenneth Hann

Principal Engineer

Artwork:Tanja Hann

November 1, 2011 1

Packet Clocks...

the first migration

Land of

Phase

Data

Com

Republic

Legacy

Land

Packet Clocks...

the first migration

Land of

Phase

Data

Com

Republic

Legacy

Land

Packet Clocks...

the first migration

Land of

Phase

Data

Com

Republic

Legacy

Land

10/25/10 5

Agenda

1. From “here”...2. Timely progress3. Supporting PTP migration

4. To Phase (eventually)

5. Conclusions

1st Migration 2nd Migration

1. From “here”:

November 1, 2011 6

• mobile FDD• Ethernet backhaul• that “last E1”

From Legacy Sync ...to SyncE

RNCN x E1

“all SyncE”

Network

RNC

E1

N x E1

Operator Network

(TDM)

Ethernet

Network

SyncE flow

From Legacy Sync ...to PTP

RNCN x E1

Network

(3rd party)

PTP

masterPTP

slave

PTP timing flow

(G.8265.1)

RNC

E1

N x E1

Operator Network

(TDM)

Network

(3rd party)

From Legacy Sync ...to Hybrid networks

RNCN x E1

Network

(3rd party)

PTP

masterPTP

slave

RNC

E1

N x E1

Operator Network

(TDM)

Network

(3rd party)

SyncE

PTP timing flow

SyncE flow

2. Timely Progress

November 1, 2011 10

• Network limits G.8261.1• Packet Equipment Clock model G.8263• PEC “knowledge base” G.8260

Output limits for a packet Clock(frequency / FDD applications)

112G / 3G / LTE mobile requires 50ppb frequency stability

2us

18us

MTIE

2us +16ppb

18us + 50ppb

Or...

18us + 16ppb

50ppb

9 µs

Observation

interval τ (s)32

MTIE

0.2

16ppb

1125

18 µs

640.05

G.8261.1 Sneak Preview

Factors impacting Packet clock “performance”:

•Local oscillator stability

•Accuracy of timestamps

•Sync rate

•PDV characteristics of the network

•PDV filtering in the packet clock

•Packet selection algorithm

•Number of synchronization flows in Ensemble

•Ensemble combining algorithm

•Adaptive clock recovery algorithm

None Some of above being standardized

2010

2011

Model of a frequency PEC (G.8263)

November 1, 2011 13

Noise

Amplitude

(us)P

acket s

ele

ctio

n

PECoutput

Ensem

ble

2nd order PLL

Master_1

Master_n

...

PEC output

for worst case input

November 1, 2011 14

Worst case

Noise

Amplitude

OutputFFO2nd order

PLL

Packet Equipment Clock model

– not just ”secret plans and clever tricks”

November 1, 2011 15

0

10

20

30

40

50

60

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Max o

utp

ut

FF

O f

or

all f

req

uen

cie

s (

pp

b)

Time Constant (seconds)

100µs PDV Triangular noise

200µs PDV Triangular noise

500µs PDV Triangular noise

16ppb objective

5000s line

PEC Time constant guarentees a

noise tolerance

10/25/10 16

3. Supporting PTP migration

(Frequency FDD)

• PDV metrics

• Clock output monitoring

• Live network deployments

Monitoring of the Synchronization

network

Mobile networks:

– need synchronization <50ppb

– May be >10,000 nodes

– Some must migrate to IEEE1588

PECs viewed with suspicion

– Are fairly new

– Telecom standards still evolving

– Performance partially dependent on network conditions

17Operators need to be conservative

Packet Metrics – work in progress ...

10/25/10 18

0

10

20

30

40

50

60

1 10 100 1000 10000

Available, but...

Hard to interpret...

Needs mapped to FFO

10/25/10 19

True PEC output monitoring

(Built-in wander meter)

Needs a reference, but...

Fortunately legacy provides

the reference (temporarily).qPEC qSD

H

IEEE1588 Clock Monitoring

Phase

comparitor

Node

Clock

qSD

HqPEC...

TIE

+

MTIE > Mask Alarm

TIE measurement

TIE measurements

21

MTIE measurements

(up to 10 x 24h)

Which of my 10,000 nodes should I monitor?

March 14, 2011 - DRAFT 22

Filter for 1588 ”Mask Crossed”

alarms

Change mask for senarios

Why not monitor all 10,000?

Network management

Supports 1588 clock monitoring

March 14, 2011 - DRAFT 23

Select reference (for Migration use ”last E1”).

Configure MTIE mask and monitoring period

Automate configuration using tools; rules and macros

Set Fall Back List priorities (determines node clock)

E.g. Initially E1 then switch to PTP

Large scale evaluation of IEEE1588

performance (TDM to IEEE1588 migration)

Work flow:

1. Configure clock monitoring (Node clock = E1)

2. Periodically during migration

– filter faults to show synchronization “trouble spots”

– launch clock monitoring on selected node

– optionally “tighten MTIE mask” for scenarios

3. Preference PTP over E1 (Node clock = PTP)

(clock selection process does the “switchover)

4. Decommission the “last E1” from nodes

March 14, 2011 - DRAFT 24Perhaps leave a few measurements points...

10/25/10 25

4. Future Directions(phase synchronization TDD/LTE adv.)

•Phase requirements (new network)

•Telecoms boundary clock

•Network phase & service phase

10/25/10 26

Telecom Phase and frequency solutions are very different...

... but same management (SSM) for both

Prepare for the ”phase migration”

LTE-TDD and LTE-advanced

– Require phase synchronization

– 1us or better accuracy

GPS extension using IEEE1588

– Standardization work ongoing

– Nodes ”T-BC Hardware Ready”

10/25/10 27

RNC

Network(Ethernet)GPS

GPS

PPS

Initially islands around GPS

SyncE

Microwave

links

Synchronization TopologyProvisioned, uses ”SSM” for ring protection

Migration to support phase means

– Upgrading PRC to PRTC

– Upgrading EEC’s to T-BC’s

10/25/10 28

SDHSyncE

10GRNC

L3L2L3 L1

Topology management is the same for phase

PR CT

Network timing flow

Network phase flow

Phase sync needs 4 timestamps

Delivery mechanisms differ...

November 1, 2011 29

Master Slave

T1T2T3

T4

T4

IEEE1588 Delay

Request Mechanism

T2T1

T4T3

ESMC timestamp mechanism

(Phase Synchronous Ethernet)

a)

b)

c)

T2T1

T4T3 IEEE1588 Pdelay Request Mechanism

(Sync message free for ”Service Phase”)

10/25/10 30

L1 SyncE

L2 Ethernet

T-BC

L3 IPService

Phase(s)

Network

Phase

Network

Frequency

Telecoms BC

Service GW

Telecoms BC

Service GW

SGW SGW

Service phase and Network Phase

E.g. When a carrier has several mobile customers...

“SSM” and the sync hierarchy remain the same!10/25/10 31

5. Conclusions

Everyone is leaving “Legacy Land” on...

– SyncE; PTP; Hybrid (or anything that floats)

Packet Equipment clocks - ready for Ethernet prime-time

PEC output monitoring gives a confidence boost

– Last service of the “Last E1”

– Large-scale, live network, field monitoring is available

Prepare for 2nd migration

– Phase support needs new clocks (Nodes “HW phase ready”)

Thank you!

Questions?

Enabling the mobile Internet

November 1, 2011 33

10/25/10 34

A PEC’s got to know it’s limitations

PTSF