70 Packet Synch

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Mobile Synchronisation

All Rights Reserved © Alcatel-Lucent 2008

Rolf Sperber (Material from Dave Sargent)

[email protected]



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

All Rights Reserved © Alcatel-Lucent 2008,

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



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


(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?



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


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)



TDM

Network

TDM

Network

Reference

Clock

Synchronization in Heterogeneous Environments


PacketNetwork

Packet

Switch

CES

Packet

Switch

CES

TDM

Switch

TDM

Switch

E1 TDM E1 TDM



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


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



Timing Measurements


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.



Time Interval Error (TIE)

Fundamental metric for comparing clocks




Carrier Frequency Accuracy for Handoff Control


Handset expects to see the carrier at F2

If F2 > 50ppb from nominal, handset wont find it and call drops.



Synchronization Options




Ways to Synchronize

Overlay Synchronization Network

TDM network in parallel exists

Interim Solution

Distributed Reference Clock Solution

PRC traceable via GPS

Future proof solution


ranspor o m n n orma on v a pac e e wor

Packet based solutions

PHY based solutions



Reference

Clock

TDM Network

Overlay Network for Synchronization


Packet NetworkAsynchronous

Packet

SwitchCES

Packet

Switch

CES

TDM

Switch

E1 TDM

SynchronizationPurposesTDM

Switch



Distributed PRC for Synchronization (GPS)

Reference

Clock

TDM Network

for Classical Time

Distribution


Packet NetworkAsynchronous

Packet

Switch

CES

Packet

Switch

CES

TDM

Switch

E1 TDM

TDM

Switch



Primar

Slave

Hierarchical Clock Distribution


SwitchCES

TDM

SwitchReferenceClock

Packet

Switch SwitchCES

TDM

Switch

TDM

Switch Application

Master



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


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)



TDM

Network

TDM

Switch

TDM

Switch

Reference

Clock



PacketNetwork

SwitchCES SwitchCESE1 TDM E1 TDM

Clock Information

Transport

Interworking

Function

Interworking

Function



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


Less stringent requirements for intermediate nodes



TDM

Network

TDM

Network

TDM

Switch

TDM

Switch

Reference

Clock


PacketNetwork

SwitchCES SwitchCESE1 TDM E1 TDM

Clock Information

Transport

Interworking

Function

Interworking

Function



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.


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



Packet

Switch

CES

Packet

Switch

Query if neighbour

is G.8261 compliant

Packet

Switch

CES

Packet

Switch

Standard Packet

Forwarding

Synchronous Ethernet G.8261


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



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


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



Network Sync Options


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


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



Evolving Network Sync Options

IEEE 1588v2 Slave

Sync (1588 messageexchange)

Ethernet

Node B

Node B

Node B

7705 SARAggregation

Node


PrimaryReference

Clock

Sync


.

Sync

Ethernet

Node B

Node B

Node B

7705 SARAggregation

Node


PrimaryReference

Clock

Sync



Testing 8261




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


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



SyncE in 7750 / 7705




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

All Rights Reserved © Alcatel-Lucent 2008,All Rights Reserved © Alcatel-Lucent 200927

Timing over Synchronous Ethernet performance test

Test over a large network:

- Transport over 24 nodes

Test performance over long duration

- For 10 hours

Documents

70 Packet Synch