Dual Latency ADSL

5/22/2018 Dual Latency ADSL

1/51All Rights Reserved Alcatel-Lucent 2006, #####

Dual latency discussion (ADSL2+)

Victor Cortijo Technical Presales Expert Group

November, 2007


2/51All Rights Reserved Alcatel-Lucent 20072 | UPC DSL technology | July 2007

Index

1. Impulse noise and its protection

2. Problem statement and dual latency solution

3. Customer examples

4. Implementation complexities and problems

5. Performance (HSI/video/VoIP/gaming)

6. Final conclusion

7. Artificial noise



1Impulse noise and its protection



Impulse noise problem

0 2 4 6 8 10 12 14 16 18 20-0.015

-0.01

-0.005

0

0.005

0.01

0.015

Time [DMT Symbols]

Voltageon100Ohm

s[volts]

-2 -1 0 1 2 3 4 5 6 7

x 10-3

-1.5

-1

-0.5

0

0.5

1

1.5

Neon 6

Neon lamps and economic lamps:

e.g. turn on of TL lamp

Longest burst observed

28 DMT symbols

0.2 DMT symbols

ERRORS



INP & Delay in ADSL2+

Protection (INP) = combination of interleaving and RS overhead.

Complex formula for data rate - can be simplified to

INP bigger => net data rate smaller

Max delay smaller => net data rate smaller

Big issue both driving factors (more protection, less delay)

drive to less net data rate

maximum achievable bit rate also capped by interleaver memory size and

maximum 1/S

Net_data_rate/Total_data_rate = 1-(INP / (2 delay[ms]))



2Problem statement and dual latency

solution



Problem statement

What is the optimal INP_min/max_Delay

combination for triple play (ADSL2+) with single

latency?

Is there even a reasonable solution?

As a consequence, is dual latency reallyneeded or not?


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All Rights Reserved Alcatel-Lucent 20078 | UPC DSL technology | July 2007

3Customer examples


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Dual latency

In practice

all 3-play deployment today using ALU equipment is single latency (on

ADSLx and VDSL2) operators that initially put dual latency as a requirement finally decided to deploy

single latency after consideration of all aspects

lack of CPE support for dual latency today ; no dual latency IOP today

no IOP tests have been done at UNH plugfests with dual latency

All 3-play over xDSL using ALU equipment is offered successfully without duallatency today


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INP_min/delay_max for triple play in real life

Examples (information has been summarized because of confidentiality):

VDSL2 customers: INP ranges from INP=1 to INP=2 with delay=8ms and some

type of higher layer retransmission is used in all (or most of the) cases

ADSL2+ customers: INP ranges from INP=1 to INP=4 with delay=8ms in all

cases

one of the customers uses INP=1, delay=8ms for both upstream and downstream

with no higher layer retransmission

Only one of the customers uses higher layer retransmission with settings

INP=2,delay=8ms downstream
http://www.swisscom.com/GHQ/?lang=fr


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4Implementation complexities and problems


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Implementation complexities and problems (1)

Need for selection mechanism to associate incoming traffic with a bearer on

DSL line

Dual latency is standardized at the physical layer but there is no correct standard

specification on how the traffic should be split or aggregated above these

interfaces and this can result in interoperability and other deployment issues.

If Dynamic Rate Repartitioning (DRR) is not well defined, there is no bandwidth

sharing between bearers, meaning that bandwidth is wasted if one of the services

is not being used.

Dual latency risks big interoperability issues

for each DSL line, different queues may be required per bearer if different QoSclasses are mixed over same bearer. Also, a scheduler resource or instance is

required per bearer on each DSL line (complexity of scheduler depends on number

of service types that can be mixed on single bearer).


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The most attractive solution (QOS model)consists in associating each of the QOSqueues to one of both latency channels. This way the selection of the QOS queue

(based on Priority bit) automatically results in the selection of the latency channelBUT..

..to offer a QoS-based solution, we would need:

agreements from the CPE suppliers to adopt the same model.

Most ATM CPE's are expected to use separate PVC's across the different latencychannels.

confidence that the Priority bits are well controlled through the network.

confirmation that such implementation suits the different customers.

the acceptance of or a solution to the technically feasible but controversialimplementation for ATM where a PVC channel can by principle not be split on twobearers.

Dual latency puts end-to-end requirements

to ensure that different services are mapped on proper latency bearers


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Each bearer has to be addressable on the DSL line

DSL modem ASICs and interface between network processor and DSL modem ASICsneed to support a double number of physical port addresses

Number of objects to be managed doubles

multiple bearers on a same DSL line have to be managed (configuration, fault and

performance mgmt) as different physical lines

with some dependencies between managed objects (bearers), e.g. maximum

aggregate bandwidth on a physical DSL line determines possible provisioning ofbandwidth on each of its bearers

Dual latency increases operational complexity


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5Performance (HSI/video/VoIP/gaming)

ALU investigation


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Performance summary

Service Packet loss sensitivity Delay sensitivityVideo without correction at

higher layers

High

packet loss 107to 109

Very low

(dejittering buffer of seconds)

Video with correction at higher

layers

Low

packet loss 5%

Very low

(dejittering buffer of seconds)

Web browsing Medium

packet loss 0.1%

High (if RTT is low)


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Performance conclusion

guaranteed correction of 2 successively corrupted DMT symbols (INP=2)

improves video quality and large file downloads in environments with strong

impulse noise

medium interleaving delay (8 ms) is fine for gaming, VoIP and web browsing

(HTTP)

From performance point of view, single latency is

enough INP=2 in combination with delay of 8 ms is good combination for

downstream.

good Reed Solomon efficiency (R/N = 1/8)

upstream delay and INP values can be less than for downstream

But, is the data rate in this case sufficient for triple

play?


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Dual latency

Example: maximum achievable bit rates in function of INP & Delay

26

Upper DS performance limits for Amd1 ADSL2+ standard

40248112144552224426042278092955663

40248112144552224426042278092955632

40248112144552224426042278092955616

0811214455222442604227809295568

00761621092257182761229556400076162092825718295562

000000295561

1684210.50

INP_min

d

elay_

max(ms)

CPE has to be compliant !

= INP 2, 8 ms delay

Limitations: (1/S)max=16, Dmax =511, Max Interleaver Memory=16k


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Dual latency


32

Upper DS performance limits for amd.3 ADSL2+ standard

539310844190922470327217283942955663

539310844190922470327217283942955632

402410844190922470327217283942955616

0811219092247032721728394295568

00761621092257182761229556400076162092825718295562

000000295561

1684210.50

INP_min

d

elay_

max(ms)

CPE has to be compliant !

Limitations: (1/S)max=16, Dmax =511, Max Interleaver Memory=24k

= INP 2, 8 ms delay


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Result with CT562plus

INP=2 with Delay 16/8/4ms vs INP=0/Delay=16ms


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Result with ST716

INP=2 with Delay 16/8ms vs INP=0/Delay=16ms


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6Final conclusion


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Final conclusion

Dual latency is not needed in the current triple

play (ADSL2+) scenario Single latency performance is guaranteed with INP=2 and

max_delay = 8 ms

Single latency data rate is enough to deploy triple play

Other operators deploying triple play successfully with singlelatency

Dual latency (if implemented) increases

dramatically the interop and operationalcomplexity of the solution, leading to other type

of errors/limitations/compromises.


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7Artificial noise


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0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.0016.00

20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 0:00

1stNoise increase

(neighbor modem)

2nd Noise increase

(strong radio signal)

Service interruptions:resyncs result in minutes

of downtime

Service degradation:lower bandwidth due to

higher noiseBandwidth(Mbp

s)

time

Line instability cause and visible effects

A closer look at a DSL line during prime time (8pm-midnight):

noise

stable DSLvideo affected by

packet loss

Excessive transmission errorsSpontaneous DSL line resynchronizations

stable DSLvideo affected by

line resync


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Stabilizing an unstable line with Artificial/Virtual Noise

Original situation high bandwidth but unstable

Traditional solution: High Noise Margin stable but reduced bandwidth

The Alcatel-Lucent solution: Artificial/Virtual Noise stable and high bandwidth

Bandwidth

(Mbps)

time

noise

noise

noise

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 0:00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 0:00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

20:00 20:30 21:00 21:30 22:00 22:30 23:00 23:30 0:00

stable @11.6 Mb/s

stable @4.7 Mb/s

2 resyncstable @ 9.7 Mb/s


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Margin

frequencies ()

Receiver Noise

Artificial Noise (ADSL) / Virtual Noise (VDSL)

frequencies ()

MarginMargin

Receiver Noise

Artificial /

Virtual

Noise

resyncs

Unstable line

Service interruptions

Artificial/Virtual noise guarantees DSL stability whilst keeping Noise Margin lowfor maximum bandwidth availability

Neighbour switches

on DSL modem,

generating crosstalk

Dynamic noise

(crosstalk) exceeds

configured margin

Noise margin adapts

to accomodate virtual

noise

Dynamic noise will not

exceed noise margin(on top of A/V noise)

no resync

Noise margin can

remain low, for max.

bandwidth

No resyncs

Stable line

No interruptions

PSD

(dBm/Hz

)

PSD

(dBm/Hz

)


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Artificial Noise / Virtual Noise field results

Transmission errors (CVs)

2 ~3 day monitoring>3500~1 day monitoring

problem line

3500 errors/day

14.9Mbps

Multiple resyncs

Same line with Artificial Noise


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StableDSL R1.0

ADSL Artificial Noise

Unique Alcatel-Lucent solution

invented by ALU patent pending

Works with all deployed CPEs

VDSL Virtual Noise

Invented by ALU patent pending

Included in standard (optional)48pVDSL2

48pMulti-DSL

Artificial/Virtual noise in ISAM Network Analyzer

Alcatel-Lucent consultancy groups help operators stabilize their lines

1 2

3

Premium Package never included in base price

DSL line troubleshooting Automated Artificial / Virtual Noise

configuration

Automated line analysis

Access Network Design

& Transformation (AND&T)

Logical and physical network design:

introduction of new DSL flavours

introduction of new Triple Play services

Access Network OperationsOptimizations (ANOO)

Operational optimization of DSL networks:

Troubleshooting & Tuning of networks

5520 AMS, 5580 HNM and 5530 NA


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StableDSL R1.0 : Practical Information

Availability: today

Virtual Noise: ISAM R3.1 ETSI, Artificial Noise: ISAM R3.3 (DR5 Aug07)

Network Analyser support: AN/VN analysis R5.2 (Jul07)

Virtual/Artificial noise should be implemented independently of theINP/Delay settings

Helps with resynchronizations and line stability

Helps in conditions of high repetitive noise


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Backup


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Impulse noise protection

Reed Solomon plus interleavingMessagevector

Ctrl Data to be transmitted

Transmitted Data

Bloc 0 Bloc 1 Bloc 2

CtrlCorrection CtrlCorrection CtrlCorrection CtrlCorrection CtrlCorrection

Bloc 3 Bloc 4

Bloc 0 Bloc 1 Bloc 2 Bloc 3

Burst errors

6 lost bytes

1 Byte error

per bloc!


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Impulse Noise Protection (INP) in ADSL2(+)


How much of the DMT symbol is protected?

Protection via Reed Solomon and extended via interleaving

Which parameters influence the INP

S = # DMT symbols per RS word

D = interleaving depth (# of combined RS words used)

N = Number of bytes per RS word (1 255 bytes)

R = Number of RS overhead bytes (0 16 bytes)

(ms)delay4

DS

N

RDS0,5INP


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Step 1: protection for 1RS / 1DMT symbol

NOinterleaving introduced

R=overhead bytes N=Total bytes K= payload bytes

Correction on payload = R/2

What part of the DMT symbol is protected?

Number of correctable bytes over number of bytes in DMT symbol INP = DMT protection = payload correction / N = R / (2xN)

K R

DMT symbol


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Assume 1 RS word / 4 DMT symbols & NOinterleaving

S = # DMT symbols per RS word = 4

We have seen before that RS correction = R/2

How much of the DMT symbol is protected? RS word is now spread over 4 DMT symbols

With R=16 you have 8 correctable bytes over 4 DMT symbols

INP = (# correctable bytes) / (#bytes in a DMT symbol)== (R/2) / (N/S) = (S x R) /( 2 x N)

INP increases with a factor S

Step 2: protection for 1RS / S DMT symbols

DMT DMT

RS

DMT DMT


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...

1 2 3 4 5 6

Step 3: introducing interleaving

Correction has improved by a factor D

Errorred bytes are spread over D RS words

Payload correction = D x R/2

DMT protection has as such also increased

= # correctable bytes / N = (DxR)/(2xN)

BufferD

D = interleaving depth

N = number of bytes per RS word

incoming

outgoing

Max. 255

Bytes

..

N

B1 B1 B1 B1 B2 B2 B2 B2 Bx Bx Bx Bx Bz Bz BN BN BN BN...

Assume 1 interleaved RS word / DMT symbol

Size N

Max. 64


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Step 4: all together

RS introduces a correction = R/2

RS correction presented by parameter R

Interleaving introduces an improvement on the number of correctable bytes

Interleaving represented by parameter D

S factor introduces an impact on the number of correctable bytes per DMT

symbol

INP = (S x # correctable bytes) / N

= S x R x D / (2 x N)


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conclusions

INP = S x D x R / 2 x N

How to increase the INP

Increase S > increases the introduced delay

Increase D > increases the introduced delay

Increase R > Decreases the available bitrate

Decrease N > Decreases the available bitrate

When configuring a DSL port a max delay needs to be given and a minimum INP

This will impact the max. possible bitrate


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Reed Solomon plus interleaving

Messagevector

Checkbytes Data to be transmitted

Transmitted Data

RS word 0 RS word 1 RS word 2

Received Data

CheckCorrection

RS word 3 RS word 4

RS word 31 Byteerror

per bloc!

1 DMT symbol in error:

5 lost bytes

CheckCorrection CheckCorrection CheckCorrection CheckCorrection

D=31

N=q*I=15

K=9 R=6

I=5

S=5/15

RS word 4RS word 0 RS word 1 RS word 2


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INP & Delay in VDSL2

Protection (INP) = combination of interleaving depth and RS overhead.

Complex formula for data rate - can be simplified to

_ _ 2 _1_ _ _

n nn

n n s

total data rate INP minr net data rate delay max f

delay_maxnis in milliseconds

fsis the data symbol rate in ksymbols/s

INP_min bigger => net data rate smaller

Max delay smaller => net data rate smaller

Big issue both driving factors (more protection, less delay)

drive to less net data rate


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HSI performance

HSI performance is determined by

packet loss due to stationary and impulsive noise if packet loss is too high, TCP goes in congestion avoidance too often

use interleavedmode rather than fast mode

file size

TCP does not get out of slow start before file transfer is over

use fastmode rather than interleaved mode

overall: interleavedis preferred for file download (onnoisy lines), fastis better for web browsing (on very highcapacity XDSL lines)


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Video performance

Video quality is determined by

bit rateuse a high enough video bit rate (1.5 Mb/s for SDTV, 8Mb/s for HDTV)

use a state-of-the-art codec (e.g. H.264)

packet loss

video is very sensitive to packet loss

every lost packet is visible when MPEG-Transport Stream is used different (new) transport mechanisms exist that may offer better

robustness (less visual disturbance) against packet loss

use interleavedmode to protect against packet loss

use FEC on packets or a retransmission scheme to protect against remaining packet

loss

Video can tolerate some delay

additional DSL bit pipe delay will have almost no impact on overall zapping time

overall: interleavedis recommended but can work infastmode too with FEC or retransmission at packet level


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VoIP performance

Voice quality is determined by

end-to-end delay total budget is 150ms without any drop in quality and even 400ms if a slight loss in

interactivity is allowed; however, XDSL line requirement will be something less

fastmode is fine; but additional delay of interleavedmode (e.g. 8 or 16 ms) is notdramatic

packet loss

tolerable amount of packet loss is a few percent

interleavedmode is fine; but normally also no problem in fastmode

overall: slight preference for (medium) interleavedmode but works fine in fastmode too


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Gaming performance

Gaming performance is determined by

(twice) client-server delay (Ping time) an additional 60-80ms delay (over the adversarys) seems to negatively impact

gaming performance

fastmode is fine; but additional delay of interleavedmode (e.g. 8 or 16 ms) is notdramatic

packet loss

does not seem to be crucial

no problem in interleavedand fastmode

overall: slight preference for fast mode but works fine in(medium) interleavedmode too

Dual latency


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Dual latency

Example: maximum achievable bit rates in function of INP & Delay (Amd 1)

x 4000 symbols/sec = bps

Total Data Rate (bits/symbol)


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Increasing DSL stability for IPTV StableDSL R1.0

DSL line stability is critical

Errorspe

rday

1

10

100

1000

IPTV Errors visible

>> complaints

InternetErrors hardly visible

CLEC

HSI/ADSL2+

ILEC

HSI/ADSL

ILEC

IPTV/ADSL2+

CLEC

IPTV/ADSL2+

ILEC

HSI(512k)/ADSL

Up to 25% of DSL lines potentially unstable

Stable lines

Potentially unstable: crosstalk

Solution: Artificial/Virtual noise

0% 20% 40% 60% 80% 100%

More complaintsLess qualifying lines Lower take-up rate/higher churn


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Difference with VDSL2


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Difference with VDSL2

Everything stated remains exactly the same

but.. Due to different technology, achievable bit rates are different than

in ADSL2+ (see next slides)


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VDSL2 PHY fault correction

Alcatel VDSL2 implementation allows independent configuration of INP and

delay on per port basis max interleaving Delay can be configured in steps of 1ms in range of 0 to 63

ms (delay 2ms for interleaved path)

min INP can be configured in steps of 0.1 DMT symbol in range of 0 to 16

DMT symbols

max achievable bit rate is function of combined settings for INP and delay

Example: downstream for profile 12a/b (simulation with estimated null loop

performanceThroughput

Delay Error

Correction (INP)

BALANCE

2 4 8 16

2 13056 0 0 0

4 37632 13056 0 0

8 60242 37632 13056 0

16 60242 39168 24084 13056

32 60242 39168 24084 13645

INP_min

delay_max

(ms)

Net Data Rates

Note: The bit rates presented in the table are upper limits which might not be practical or feasible in

typical VDSL2 deployment scenarios.

Dual latency


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Dual latency


0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400

TP150 loop length [m]

bitrate[Mb

/s]

fast down

fast up

INP=2, delay=8ms downINP=2, delay=8ms up

INP=4, delay=16ms down

INP=4, delay=16ms up

INP=8, delay=63ms down

INP=8, delay=63ms up

NVLT-A

measurementconditions NVLT-A (R3.2) profile 12a PSD mask: 998-M2x-A -140 dBm/Hz AWGN loop TP150


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