Dual Latency

All Rights Reserved © Alcatel-Lucent 2006, #####

Dual latency discussion (ADSL2+)

All 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


1 Impulse 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]

Volta

ge o

n 10

0 Oh

ms

[volt

s]

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

x 10-3

-1.5

-1

-0.5

0

0.5

1

1.5Neon 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 smallerMax 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]))


2 Problem 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 really needed or not?


3 Customer examples


Dual latencyIn 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 dual latency today


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


4 Implementation complexities and problems


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

QoS classes 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).


Implementation complexities and problems (2) The most attractive solution (QOS model) consists in associating each of

the QOS queues 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 channel BUT..

..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

latency channels. 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 controversial

implementation for ATM where a PVC channel can by principle not be split on two bearers.

Dual latency puts end-to-end requirements to ensure that different services are mapped on proper latency bearers


Implementation complexities and problems (3)

Each bearer has to be addressable on the DSL line DSL modem ASICs and interface between network processor and DSL

modem ASICs need to support a double number of physical port addressesNumber 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 of bandwidth on each of its bearers

Dual latency increases operational complexity


5 Performance (HSI/video/VoIP/gaming)ALU investigation


Performance summary

Service Packet loss sensitivity Delay sensitivityVideo without correction at higher layers

Highpacket loss 10–7 to 10–9

Very low(dejittering buffer of

seconds)Video with correction at higher layers

Lowpacket loss 5%

Very low(dejittering buffer of

seconds)Web browsing Medium

packet loss 0.1%High (if RTT is low)

<<RTTFile download Medium

packet loss 0.1%Medium (if RTT is low)

<<RTTVoIP Low

few % packet loss acceptable

Medium (total budget is 150 ms but requirements for DSL may

be order less)Multiplayer shooting game Low

few % packet loss acceptable

Medium/high (total budget is 100 ms but user perception may require

low delay)MMORPG (Massively Multiplayer Online Games)

Low packet loss 10%


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?


Dual latencyExample: maximum achievable bit rates in function of INP & Delay

26

Upper DS performance limits for Amd1 ADSL2+ standard

402481121445522244260422780929556634024811214455222442604227809295563240248112144552224426042278092955616

0811214455222442604227809295568007616210922571827612295564000761620928257182955620000002955611684210.50

INP_minde

lay_

max

(ms)

CPE has to be compliant !

= INP 2, 8 ms delayLimitations: (1/S)max=16, Dmax=511, Max Interleaver Memory=16k



32

Upper DS performance limits for amd.3 ADSL2+ standard

539310844190922470327217283942955663539310844190922470327217283942955632402410844190922470327217283942955616

0811219092247032721728394295568007616210922571827612295564000761620928257182955620000002955611684210.50

INP_minde

lay_

max

(ms)

CPE has to be compliant !

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

= INP 2, 8 ms delay


Result with CT562plus INP=2 with Delay 16/8/4ms vs INP=0/Delay=16ms


Result with ST716 INP=2 with Delay 16/8ms vs INP=0/Delay=16ms


6 Final conclusion


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

single latency

Dual latency (if implemented) increases dramatically the interop and operational complexity of the solution, leading to other type of errors/limitations/compromises.


7 Artificial noise


0.002.004.006.008.00

10.0012.0014.0016.00

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

RESYNC

1st Noise increase (neighbor modem)

2nd Noise increase (strong radio signal)

Service interruptions: resyncs result in minutes of downtime Service degradation: lower bandwidth due to higher noise

Band

widt

h (M

bps)

time

Line instability – cause and visible effectsA closer look at a DSL line during prime time (8pm-midnight):

RESYNC

noise

stable DSL video affected by packet loss

Excessive transmission errorsSpontaneous DSL line resynchronizations

stable DSL video affected by line resync


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

Band

widt

h (M

bps)

time

noise

noise

noise

0.002.004.006.008.00

10.0012.0014.0016.00

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

0.002.004.006.008.00

10.0012.0014.0016.00

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

0.002.004.006.008.00

10.0012.0014.0016.00

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


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 low

for maximum bandwidth availability

Neighbour switches on DSL modem, generating crosstalkDynamic noise (crosstalk) exceeds configured margin

Noise margin adapts to accomodate virtual noiseDynamic noise will not exceed noise margin (on top of A/V noise) – no resyncNoise margin can remain low, for max. bandwidth

•No resyncs•Stable line•No interruptions

PS

D (d

Bm

/Hz)

PS

D (d

Bm

/Hz)


Artificial Noise / Virtual Noise – field results

Transmission errors (CV’s)2

~3 day monitoring>3500

~1 day monitoring

problem line3500 errors/day14.9MbpsMultiple resyncs

Same line with Artificial Noise<1 error/day12.0MbpsNo resyncs

Preliminary field results are excellent


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)

48p

VDSL

248

p M

ulti

-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 Operations Optimizations (ANOO) Operational optimization of DSL networks: Troubleshooting & Tuning of networks 5520 AMS, 5580 HNM and 5530 NA


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 the INP/Delay settings Helps with resynchronizations and line stability Helps in conditions of high repetitive noise


Backup


Impulse noise protection

Reed Solomon plus interleavingMessage vector 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 errorper bloc!


Impulse Noise Protection (INP) in ADSL2(+)

Impulse noise protection 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)delay 4

DS

NRDS0,5INP


Step 1: protection for 1RS / 1DMT symbol

NO interleaving 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


Assume 1 RS word / 4 DMT symbols & NO interleaving 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


...

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 depthN = number of bytes per RS word

incoming

outgoing

Max. 255 Bytes

..

N

B1B1B1B1B2B2B2B2 BxBxBxBx Bz Bz BN BN BN BN...

Assume 1 interleaved RS word / DMT symbol

Size N

Max. 64


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)


conclusionsINP = S x D x R / 2 x NHow 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


Impulse noise protection

Reed Solomon plus interleavingMessag

e vector

Check bytes 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 Byte error

per bloc!

1 DMT symbol in error:5 lost bytes

CheckCorrection CheckCorrection CheckCorrection CheckCorrection

D=31

N=q*I=15K=9 R=6

I=5

S=5/15

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


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 minrnet data rate delay max f

delay_maxn is in milliseconds

fs is the data symbol rate in ksymbols/s

INP_min bigger => net data rate smallerMax delay smaller => net data rate smaller

Big issue – both driving factors (more protection, less delay) drive to less net data rate


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 oftenuse interleaved mode rather than fast mode

file size TCP does not get out of “slow start” before file transfer is overuse fast mode rather than interleaved mode

overall: interleaved is preferred for file download (on noisy lines), fast is better for web browsing (on very high capacity XDSL lines)


Video performance

Video quality is determined by bit rate

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

packet lossVideo can tolerate some delay

additional DSL bit pipe delay will have almost no impact on overall zapping time overall: interleaved is recommended but can work in

fast mode too with FEC or retransmission at packet level


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

fast mode is fine; but additional delay of interleaved mode (e.g. 8 or 16 ms) is not dramatic

packet loss tolerable amount of packet loss is a few percentinterleaved mode is fine; but normally also no problem in fast mode

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


Gaming performance

Gaming performance is determined by (twice) client-server delay (Ping time)

an additional 60-80ms delay (over the adversary’s) seems to negatively impact gaming performance

fast mode is fine; but additional delay of interleaved mode (e.g. 8 or 16 ms) is not dramatic

packet loss does not seem to be crucialno problem in interleaved and fast mode

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


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

x 4000 symbols/sec = bpsTotal Data Rate (bits/symbol)


Increasing DSL stability for IPTV – StableDSL R1.0

DSL line stability is critical

Erro

rs p

er d

ay

1

10

100

1000

IPTV Errors visible>> complaints

InternetErrors hardly visible

CLECHSI/ADSL2+

ILECHSI/ADSL

ILECIPTV/ADSL2+

CLECIPTV/ADSL2+

ILEC HSI(512k)/ADSL

Up to 25% of DSL lines potentially unstable

Stable lines

Potentially unstable: crosstalkSolution: Artificial/Virtual

noise

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

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


Difference with VDSL2


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)


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 performance Throughput

Delay Error Correction (INP)

BALANCE

2 4 8 162 13056 0 0 04 37632 13056 0 08 60242 37632 13056 0

16 60242 39168 24084 1305632 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.



0

10

20

30

40

50

60

0 200 400 600 800 1000 1200 1400

TP150 loop length [m]

bit r

ate

[Mb/

s]

fast downfast upINP=2, delay=8ms downINP=2, delay=8ms upINP=4, delay=16ms downINP=4, delay=16ms upINP=8, delay=63ms downINP=8, delay=63ms up

NVLT-A

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

Dual Latency

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