Delivering Resilient Phase Synchronisation in

Transport Networks

Hans Sjöstrand

Product Manager - Transmode Systems AB

Trends in mobile networks impact mobile backhaul

Fiber is becoming * the * media for mobile transport networks

Macro cells become more dense, Small cells,

Multiple technologies, frequencies, cell sizes …

More stringent accuracy requirements needed to support new

functionality, like LTE coordinated multipoint (CoMP) and enhanced

inter-cell interference coordination (eICIC)

Synchronization becoming one of the most important criteria

Phase and time synchronization is required for LTE-Advanced

SLA assurance and end-to-end performance

is important

Mobile Fronthaul networks to bridge distance

between antenna and base station.

2

LTE synchronization requirements

3 Restricted

Application Frequency

Network / Air

Phase Note

LTE – FDD 16 ppb / 50 ppb N/A

LTE – TDD 16 ppb / 50 ppb ± 1.5 μs

± 5 μs

≤3 km cell radius

>3km cell radius

LTE MBMS (LTE-FDD & LTE-TDD)

16 ppb / 50 ppb ± 10 μs inter-cell time difference

LTE- Advanced 16 ppb / 50 ppb ± 1.5 to 5 μs Details in table

LTE-Advanced Type of Coordination Phase

eICIC enhanced Inter-cell Interference Coordination ± 1.5 to 5 μs

CoMP

Moderate to tight

UL coordinated scheduling

DL coordinated scheduling

± 5 μs

± 5 μs

CoMP

Very tight

DL coordinated beamforming

DL non-coherent joint transmission

± 1.5 μs

± 5 μs

UL joint processing

UL selection combining

UL joint reception

± 1.5 μs

± 1.5 μs

± 1.5 μs

Frequency requirements for earlier generations are same as above. GSM, UMTS, W-CDMA do not

have a phase requirement. CDMA2000 phase requirement is ±3 to 10 μs.

LTE-A covers multiple

techniques rather than

a single technology.

Not all features will be

deployed everywhere,

leading to differences in

real world requirements.

Figures are still in

discussion by members

of the 3GPP. Down to ±

0.5 μs accuracy.

If it wasn’t for this …. resiliency …. thing

4

Source: https://twitter.com/adtomwood/status/604267991195336704

5

Network Toolbox: Solve the nanosecond challenge

SyncE IP MPLS

Network

ROADM

λ

ROADM

λ

ROADM

λ

ROADM

λ

PRC / GM

Hybrid

Mode SC

T-TC

T-TC

T-TC

T-TC

T-TC T-TC

T-TC

T-BC T-BC

T-TC

Solutions Tools

1 Bring a PRC clock to the cell site SyncE Hybrid mode

2 Completely remove network impact on

PTP packets Transparent Clock

3 Onpath support using G.8271.1 Telecom

Boundary Clock Selected T-BC sites

PRC clock to the cell site

SyncE assisted 1588 Slave Clock

Synchronous Ethernet

7

Advantages:

• Close to the metal

• Scales without problem

• Local repair

• Stability

• Independent from network load

• Works over 100G

• Widespread implementation

8

SyncE provides outstanding Network Synchronization

Old TDM

SyncE

G.823

PRC

Better than PRC stability

long term

9

Synchronous Ethernet vital for IEEE 1588 PTP

The Long term stable PRC quality stabilized clock makes

PTP servo job easier.

SyncE

SyncE assisted

1588 Slave Clock

SyncE Frequency

1588 PTP time

PRC / GM

10

IEEE 1588 PTP Hybrid mode assisted by SyncE

Measurements of actual Phase error in G.8271.1

Traffic Matrix with a commercial Slave clock

Red line shows 1588 Slave clock phase error.

Blue line shows EMXPII SyncE assisted 1588 Slave clock phase error

1588 Slave clock

phase error:

Phase ~2.9 μs

SyncE assisted

1588 Slave clock

phase error:

Phase ~300 ns

1588 Transparent Clock

Transparent Clock operation

12

Advantages: No configuration required

Immediate

Less interoperability problems

Handles asymmetry

Makes the network “Transparent” from clock perspective

T-TC Compensates for all delays in NEs in PTP packets

Wholesale / Colocation

13

SGW nx10G

Other metro sites

Other metro sites

10G

POP 2

POP 1

Mobile operator Ethernet wholesale operator Mobile operator

Number

of sites: x2000+ x300 x50 x25

Colorless/Direction

less ROADMs

Used for business

services also

2xGbE

GbE GbE

GbE

GbE

GbE

GbE

HUB 1

HUB 2

ROADM ROADM

ROADM ROADM CE Switch

CE Switch

CE Switch

CE Switch

CE Switch

NID

NID

NID

NID

NID

CE Switch

Wholesale example

14

15

A transparent network

T-SC

Each hop contributing

with traffic generating PDV

in each output

GbE GbE GbE GbE GbE GbE GbE GbE GbE GbE

10G 10G 10G 10G 10G 10G 10G 10G 10G

GM

Measurement of packet delay variation (PDV) with and without T-TC:

16 us

PDV

Network without T-TC onpath support Network with T-TC onpath support

0.2 us

PDV

Slave clock (SC) keeps phase well within requirements Impossible for slave clock (SC) to keep phase accuracy

16

Sync performance with network transparency

G.8265.1 TC13. varying traffic load, forward (80% to 20%) and reverse (10% to 50%).

Max Phase

error ~50 us

Max Phase

error ~80 ns

No onpath support With Network Transparency

Partial onpath 1588 Boundary Clock

18

Network scalability

19

Telecom - Boundary Clock

Each hop contributing

with traffic generating PDV

in each output

IP MPLS

Network

ROADM

λ

ROADM

λ

ROADM

λ

ROADM

λ

PRC / GM

T-BC

T-BC

T-BC

T-SC

GbE GbE GbE GbE GbE GbE GbE GbE GbE GbE

10G 10G 10G 10G 10G 10G 10G 10G 10G

GM

T-B

C

T-B

C

T-B

C

Acceptable

wander

PLL absorbing wander PLL absorbing wander PLL absorbing wander

20

Sparse Onpath Support

Worst possible traffic scenario in G.8261 "Timing and synchronization aspects in packet networks "

Test Case 13: Load change

Traffic Contribution in1/10 in all 10 hops

T-SC Wander within 100ns

T-BC 1 ~150 ns T-BC 2 ~400 ns T-BC 3 ~230 ns

T-SC

GM

T-B

C

T-B

C

T-B

C

Acceptable

wander

PLL absorbing wander PLL absorbing wander PLL absorbing wander

Operate - Service and Sync Assurance

21

• Integration of Sync NMS with network

Service and Network status.

• Multilayer network visiualization.

- Ethernet, CPRI, WDM

• Sync Probes, PRCs, eNB, BBH

• Transport vendor & independent

sync monitoring combined

Pla

n

Deploy

Opera

te

THANK YOU!