Adsl Basics

HUAWEI TECHNOLOGIES CO., LTD. For internal use only

Jun 2006

ADSL Protocol Basics

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.comISSUE1.0


As the Internet develops rapidly, human

being demands more and more of the

network rate and bandwidth. The great

demand urges the network to develop

from low-speed to high-speed, sharing to

switching, and narrowband to broadband.

This course describes the Asymmetrical

Digital Subscriber Loop (ADSL), a

mainstream technology on access

network (AN).


Reference

Huawei ADSL2+ Principle and Testing Service Guide -

20050318-A http://support.huawei.com/support/pages/kbcenter/view/pr

oduct.do?

actionFlag=detailProductSimple&web_doc_id=SC0000104

718&doc_type=123-1


By taking this course, you can Know the mainstream xDSL technologies

Master the ADSL/ADSL2/ADSL2+ principles

Master the ADSL/2/2+ parameters

Know the trend of the ADSL technology


Chapter 1 xDSL OverviewChapter 1 xDSL Overview

Chapter 2 ADSL/ADSL/ADSL2+ Principles

Chapter 3 ADSL Parameters

Chapter 4 ADSL Trend


Mainstream Bearer Technology on Access Network

xDSL Flourishing

Physical lines cover a large scale and resources are exclusive in the xDSL technologies. Therefore, the xDSL technologies dominant the access network since its birth.

Ethernet Striving

The Ethernet technology that is originally applied to the enterprise LANs has developed a new market because of the birth of broadband access. The Ethernet and xDSL technologies supplement each other gradually. Nowadays, the Ethernet technology is mainly applied to the AN convergence layer and the leased lines of VIP customers.

PON Developing

The newly-appeared Passive Optical Network (PON) technology provides the gigabit bandwidth for users at a lower cost. It is no doubt that the PON technology will be a superior opponent to access network.


xDSL

The ADSL technology uses the existing twisted pairs to provide asymmetrical

upstream and downstream rate for users.

The G.SHDSL technology provides the symmetrical and high-speed leased line

access service on twisted pairs for users. It is mainly applied to the

interconnection of small and medium-sized enterprises, the base station relay of

China Mobile and the ISDN primary access.

The VDSL technology realizes the leased line connection and access. It is

mainly applied to hotel, high-speed access, video meetings, and so on.

ADSL: the Asymmetrical Digital Subscriber Line G.SHDSL: the Single-pair High-speed Digital Subscriber Line

VDSL: the Very High Speed Digital Subscriber Line


DSL Forming and DevelopingDSL Forming and Developing

xDSL Development

Middle 1970s Late 1980s Early 1990s Time Late 1990s

ISDN HDSL ADSL VDSL Other DSL

xDSL

Digital Subscriber Line


ADSL Overview

ADSL is an asymmetrical xDSL technology. It makes full use of the untapped

high-frequency band to transmit data over copper cables at high speed by

diversified modulation. Its upstream band ranges from 26 kHz to 138 kHz, and its

downstream band from 138 kHz to 1104 kHz. Its upstream rate reaches 896 kbps

and downstream 8160 kbps.

ADSL has capability of adapting rate and anti-interference. Namely, the ADSL

technology can adjust its rate to a proper degree based on the line conditions,

such as distance, noise, and so on. In the ADSL technology, the longer the

transmission distance is, the lower the transmission rate is and the more the

transmission attenuates. But the transmission distance and attenuation are not in

linear proportion.


G.SHDSL Overview

G.SHDSL is a new symmetrical subscriber line technology developed from the High-

speed Digital Subscriber Line (HDSL), the Simultaneous Digital Subscriber Line (SDSL)

and the Integrated Services Digital Network (ISDN). SHDSL has many features such as

multi-rate, optimized performance, lower power consumption for transmitting and

compatible spectrum. The rate of a single pair ranges from 192 kbps to 2312 kbps, and can

be adjusted adaptively with 8k as its granularity based on the line conditions. The

transmission reaches 3 km to 5.5 km in the G.SHDSL technology.

The SHDSL technology has the following advantages:

Extends the transmission distance of E1/V.35 (TDM) to 3 – 5.5 km that is four times or

more farther than that of the common E1/V.35.

Provides long-distance leased line access and extends the FR/CES networking distance

based on the TDM mode.

Makes full use of the existing copper cables to access broadband services asymmetrically.


VDSL Overview

VDSL is a new xDSL technology to provide symmetrical or asymmetrical upstream and

downstream rate over twisted pairs. Its transmission reaches about 1.5 km, the highest

downstream rate is 52 M (asymmetrical) and the highest upstream rate is 12 M

(symmetrical). VDSL is the fastest xDSL technology at present.

ITU-T G.993.1 serves as the VDSL.

At home or in office, VDSL is thought as the technology to get the closest transmission

rate provided by optical fibers. VDSL permits the connection by analog telephones and

by high-speed data simultaneously, but it can transmit high-speed data only with short

reach. VDSL is similar to ADSL. But it is much easier to realize VDSL because ADSL is

designed for the line conditions that are worse than those of VDSL.


xDSL Performance

Feature Comparison

xDSL Symmetry Maximum Rate Maximum

Distance (km)

Twisted

Pair

POTS

Service

G.SHDSL Asymmetrical 2.3 Mbps 5.5 1 No

ADSL Asymmetrical Downstream: 8196 kbps

Upstream: 896 kbps5 1 Yes

ADSL2+ Asymmetrical Downstream: 25 Mbps

Upstream: 3 Mbps6.5 1 Yes

VDSLSymmetrical/

Asymmetrical

Downstream: 52 Mbps (asymmetrical)

Upstream: 12 Mbps (symmetrical)1.5 1 Yes


Questions

1. What are the technical features of the ADSL, VDSL and

G.SHDSL technologies?

2. What are the applications of the ADSL, VDSL and G.SHDSL

technologies?


Chapter 1 xDSL Overview

Chapter 2 ADSL/ADSL/ADSL2+ PrinciplesChapter 2 ADSL/ADSL/ADSL2+ Principles




Chapter 2 ADSL/ADSL2/ADSL2+ PrinciplesChapter 2 ADSL/ADSL2/ADSL2+ Principles

2.1 ADSL Protocols Standardization

2.2 ADSL Principle

2.3 ADSL2 Features

2.4 ADSL2+ Features


ADSL Standards

Some international organizations take on the standardization of the ADSL technologies, including

the American National Standards Institute (ANSI), the ITU Telecommunications Union -

Telecommunications Sector (ITU-T), and the ADSL Forum.

FAMILY DESCRIPTION RATIFIED

ADSL G.992.1/ T1.413 G.dmt 1999

ADSL G.992.2 G.lite 1999

ADSL2 G.992.3 G.dmt.bis 2002

ADSL2 G.992.4 G.lite.bis 2002

ADSL2+ G.992.5 ADSL2 PLUS 2003




2.2 ADSL Principle

2.3 ADSL2 Features

2.4 ADSL2+ Features


ADSL Model

• ADSL features

1. The upstream rate reaches

896 kbps and downstream

rate 8 Mbps.

2. ADSL: Asymmetric Digital

Subscriber Line

3. Transmit voice and data on a

twisted pair simultaneously.

ADSL standards

G.992.1(G.dmt)

Standard of full-rate

ADSL

Standard of full-rate

ADSL

Standard of ADSL without signal

splitter

G.992.2(G.lite) T1.413

Twisted pairATU-R

Splitter

Splitter

PSTN

Internet


G.Lite Overview

In G.dmt mode, ADSL needs voice splitters and cannot connect the devices manufactured by different vendors. However, in G.Lite mode, ADSL does not need voice splitters and cuts down the cost of chips and installation.

Features of the low-speed G.Lite

1. G.Lite cuts down costs and needs no splitter.

2. G.Lite uses the DMT line encoding mode that performs the anti-interference well.

3. G.Lite provides asymmetrical rate, 512 kbps for upstream and 1.5 Mbps for downstream.

4. G.Lite extends the transmission distance to 7 km at most.

G.Lite is rarely used in China by taking bandwidth and market into account.


ADSL Modulation & Demodulation

As for the modulation-demodulation technology, we often use the high-speed digital signal

processing technology and the modulation coding with optimized performance to get high speed and

long distance in transmission.

So far, the ADSL modulation-demodulation system uses the following three line encoding

technologies: Quadrature Amplitude Modulation (QAM): It modulates two signals into a carrier frequency. The

amplitude modulation frequency of the two signals are the same but their phase difference is 90

degree. Carrierless Amplitude/Phase Modulation (CAP): It is based on QAM to modulate data to a single

carrier. Discrete Multi-Tone (DMT): It modulates data to multi-carrier, and the data on each carrier is

modulated by QAM. DMT is by far the mainstream modulation technology.

The DMT modulation technology dominants the market for its powerful anti-interference and popular

style.


DMT

DMT is by far the commonly-used modulation technology. It segments the transmission

band into multiple subchannels, each subchannel corresponds to a carrier of different

frequency and is modulated on the corresponding carrier in the QAM mode. The transmission

performance of the current subchannels decides the capacity of the transmitted information in

each subchannel. Information capacity defines the bits of the data modulated by each carrier.

DMT uses 4.3125 kHz bandwidth as its unit. It divides a 1 MHz band into 256 subchannels.

The POTS service occupies the band ranging from 300 Hz to 4 kHz on the telephone wire. By

taking the isolation into consideration, DMT assigns the band from 0 kHz to 25 kHz (namely,

the first six channels) to the POTS service. Therefore, only 250 subchannels are actually

assigned for transmitting digital services.

Each subchannel uses QAM in the DMT technology except the first six subchannels. QAM

piles up the output waveform since each subchannel has its own frequency, and then outputs

the piled waveform to lines. The peer receive end first restores the piled waveform based on

the frequency, and distributes them to each subchannel; then each subchannel uses QAM to

demodulate the waveform into data bits.


DMT Sub-Carrier

16 31 64 256

1.1MHz

4.3125 kHz

Voicetone

26KHz

69 kHz: upstream pilot tone

7

276 kHz: downstream pilot tone

1

Upstream subcarrierDownstream subcarrier

Available band Subchannel Data SNR

noise attenuate

s

Object 1

Object 2


ADSL System Initialization

Activate the request and confirm the procedure

Transceiver negotiation Channel analyzing Parameter switching

• Process

• Aims

The ADSL system initialization aims to test the performance of actual

subchannels, and to balance the transmission configuration between

ATU-C and ATU-R before their work, such as the upstream and

downstream rate, the number of sub-band, and so on. And finally, the

ADSL system initialization sets up an available link for communication.




2.2 ADSL Principle

2.3 ADSL2 Features

2.4 ADSL2+ Features


ADSL2 Standard

ADSL2 is developed from ADSL, its standard (G.992.3) has been

defined in June, 2002.

ADSL2 assigns the band as ADSL does, their downstream band

is 1104 kHz. Since ADSL2 uses the enhanced modulation mode, its

downstream rate can theoretically reaches 12 Mbps and its

upstream rate 1.2 Mbps or so.

The Annex I/J of G.992.3 enhances the all-digital loop mode.

Annex I works if the loop line carries the POTS service; Annex J

works if the loop line carries the ISDN service. The Annex L of

G.992.3 refers to the long-distance ADSL2.


Comparison Between ADSL2 and ADSL

ADSL2 has better performance.

Because ADSL2 uses the enhanced modulation mode, it

weakens the impact on signal from line noises, gets more line

coding gain, and promotes the rate for connecting.

ADSL2 uses the variable overhead bit, its overhead rate ranges

from 4 kbps to 32 kbps. ADSL uses the constant overhead rate

32 kbps. Compared with ADSL, ADSL2 increases its rate by 50

kbps and extends its transmission distance by 200 m. Namely,

the coverage of ADSL2 is increased by 6%.


Comparison Between ADSL2 and ADSL


New Features of ADSL2 — Lower Power Consumption ADSL2 manages the power consumption to lower the running consumption. This new function is presented as

follows:

1) ADSL2 lowers the transmitting power consumption to reduce the unexpected noise margin. Namely, lower

the futile power consumption on the premise of the service stability. The supplementary L2 mode lowers the

power consumption. This mode only guarantees the power consumption to transmit the required management

messages and synchronization signals (for example, using 1-bit constellation ) when no service data is

transmitted. In addition, when there is the user data that needs transmitting, the power consumption can be

restored at once. The power consumption in L2 mode is only 30% of that in normal operation.

2) The central office (CO) and the customer premise equipment (CPE) of ADSL2 can perform the function

“power cutback” ranging from 0 dB to 40 dB. By working with the first rule, this function can lower the power

consumption in transmission when the device runs normal. For ADSL, only CO has such a function and ranges

from 0 dB to 12 dB.


New Features of ADSL2 — Modularization Architecture

For ADSL2/ADSL2+, the ADSL transceiver is functionally divided

as follows: Transport protocol specific transmission convergence (TPS-TC)

Physical media specific transmission convergence (PMS-TC)

Physical media dependent (PMD)

Management protocol specific transmission convergence (MPS-TC)

Each sublayer is encapsulated, and messages between these sublayers

are defined. This is helpful for the interconnection between devices

made by different vendors.




2.2 ADSL Principle

2.3 ADSL2 Features

2.4 ADSL2+ Features


ADSL2+ Standards

ADSL2+ is the second generation full-rate ADSL. In 2003, ITU

presents G.992.5 that is also called the ADSL2+ standard. G.992.5

is compatible with the first generation ADSL standard, and it has

more functions, higher rate and more stable operation. For its

advantages account, ADSL2+ attracts more attention and prevails

in application.

ADSL has high rate, supports multi-service, and is maintainable.

Therefore, ADSL has been the mainstream xDSL technology

nowadays.


ADSL2+ Feature — High Rate & Long DistanceADSL2+ Feature — High Rate & Long Distance

Higher rate and Wider downstream bandsThe following figure compares the spectrum distribution of ADSL2 and ADSL2+. Compared with ADSL2, the ADSL2+ frequency ranges higher (tone 32–511), and ADSL2+ has more subbands (512). Therefore, ADSL2+ provides 24 Mbps or more for the upstream rate. Besides, ADSL2+ extends the transmission distance.


ADSL2+ Features

Longer transmit distance

The transmit distance of ADSL2/ADSL+ reaches 6.5 km or more with the rate

of 192/96 kbps

ADSL2 supports 1-bit constellation, and ADSL supports 2-bit constellation at

minimum.

ADSL2 annex L uses a new spectrum allocation. If the distance is over 4 km,

the subband higher than Tone 128 are disabled to promote the transmit power

of the subband that is lower than Tone 128, and to increase the distance.

The frame overhead can be flexibly configured to provide 28 kbps bandwidth.

This is very important in the case of long distance.

The receiver decides the tone ordering and the pilot tone. This improves the

problem that ADSL cannot be activated pilot tone because of the low SNR of

the ADSL pilot tone signal. In addition, the 2 bits carried by the pilot tone can

provide 8 kbps extra bandwidth.


ADSL2+ Features


ADSL2+ Features

Rate Binding Carriers often need provide the service of different levels for various customers. The

diversified services are made a whole through binding multiple telephone wires to promote

the rate for the home user and the business user. The ADSL2 standard supports the IMA

standard of the ATM operation to bind the services. Using the IMA technology, ADSL2

binds two or more copper wires as one ADSL connection. In this case, the downstream

rate promotion is flexible.

IMA adds a new sublayer between the physical layer and the ATM layer of ADSL. At the

transmit end, the IMA sublayer distributes the ATM data stream from the ATM layer into

multiple ADSL physical layers. The process at the receive end is on the contrary.

To bind the services of various bit error rate and delay, the IMA sublayer defines the IMA

frame, protocol and managing function in a detailed manner. Meanwhile, the IMA sublayer

requires some functions of the ADSL physical layer to be updated. For example, discard

the idle cell and the error code at the receive end.


ADSL2+ Features

More reliable running & Good spectrum compatibility The receiver decides the tone ordering based on the channel analysis result, and

selects the tone of the best performance as the pilot tone. This makes for the

stable ADSL connection.

During the negotiation, the tone is disabled, and the receiver tests the distribution

of the radio frequency interference (RFI) for bypassing the RFI signal and reducing

the crosstalk on other twisted pairs.

ADSL2+ has a good capability of dynamic adaptation. For example, it enhances

the bit swap function, and changes the line rate seamlessly and dynamically.

The power cutback of the receiver and the transmitter is 40 dB high, and reduces

the echo and crosstalk at local end.

The receiver decides the pilot tone, and avoids that the line cannot be activated

because of the line connector interference or the AM interference.

ADSL2+ shortens the negotiation process, and quickly restores the connection

synchronization from errors.


ADSL2+ Features

SRA ADSL2+ can improve the crosstalk problem by using the seamless rate adaptive

(SRA) technology. Using SRA, ADSL2+ can change the ADSL transmit power without

changing the ADSL connection rate and bit error rate. When detecting the channel

condition change, ADSL2+ adapts the rate to the change. This point is transparent to

subscribers. SRA is used for the decoupling at the modulation layer and the framing layer of the

ADSL2+ system. Decoupling enables the modulation layer to change the transmit rate

parameter, but it does not change the parameter of the framing layer. Pay attention

that the bit error will occur and cause the system restarted if the parameter of the

framing layer changes and causes the frame synchronization loss.


ADSL2/ADSL2+ Features Overview

1. Enhanced coding function

2. Lower power consumption

3. Modularization structure

4. High rate & Long distance

5. Rate binding function

6. More stable running & Good spectrum compatibility

7. Seamless rate adaptation technology


Summary

Standard/

Features

Working

Frequency (Hz)

Upstream/Down-

stream rate (bps)

Transmit

Distance (km)

Step

(kbps)

ADSL 26–138 k

138–1.1 M

896 k/8196 k 5 32

ADSL2 26–138 k

138–1.1 M

1.2 M/12 M 5.2 4

ADSL2+ 26–138 k

138K–2.2 M

3 M/25 M 6.5 4

ADSL is widely used on the existing network. ADSL2 is only a connecting point in technology development, so it is rarely used for commercial purpose. Now, ADSL is being upgraded to ADSL2+.


Questions

1. Briefly describe the three line coding technologies for ADSL

modulation & demodulation.

2. What new features does ADSL/ADSL2+ have?




Chapter 3 ADSL ParametersChapter 3 ADSL Parameters



Configuration Parameters of ADSL Service

This chapter chiefly describes the parameter in the ADSL line profile for

activating the ADSL port

ADSL transmission mode

Rate setting

Upstream/downstream channel bit swap

Trellis code

Channel mode

Noise margin

Signal attenuation



3.1 ADSL Transmission Mode

3.2 ADSL Rate Parameter

3.3 ADSL Stability Parameter


ADSL Transmission Mode

Customers use this parameter to choose a standard for activating the ADSL line. The parameter corresponds to the T1.413 issue 2 presented by ANSI and the following standards by ITU : G.992.1, G.992.2, G.992.3 (G.dmt.bis), G.992.4 and G.992.5 (G.dmt.bisplus).

The maximum downstream rate can be 8 Mbps or more in G.dmt (G.992.1, G.992.3 and G.992.5) and T1.413, but only 1.5 Mbps in G.lite. Therefore, G.dmt together with T1.413 is called full-rate transmission mode.

In addition, ITU defines a specific handshake protocol G.994.1 (G.hs) for DSL, and G.dmt and G.lite use the protocol. Therefore, G.dmt and G.lite are called G.hs mode.


Standard For Port in Negotiation

Mode Supported by CO Negotiated Mode of Line

AllAccording to the mode supported by CPE, the port can be activated by any of the following standards: G.dmt, G.dmt.bis, G.dmt.bisplus, G.lite and T1.413.

Full rateAccording to the mode supported by CPE, the port can be activated by any of the following standards: G.dmt, G.dmt.bis and G.dmt.bisplus and T1.413.

G.lite According to the mode supported by CPE, the port can be activated by the G.lite standard.

T1.413 According to the mode supported by CPE, the port can be activated by the T1.413 standard.

G.dmtAccording to the mode supported by CPE, the port can be activated by any of the following standards: G.dmt, G.dmt.bis and G.dmt.bisplus.

G.hsAccording to the mode supported by CPE, the port can be activated by any of the following standards: G.dmt, G.dmt.bis, G.dmt.bisplus and G.lite.

G992.1 According to the mode supported by CPE, the port can be activated only by the G.dmt standard.

G992.2 According to the mode supported by CPE, the port can be activated only by the G.lite standard.

G992.3According to the mode supported by CPE, the port can be activated by either the G.dmt standard or the G.dmt.bis.

G992.4 According to the mode supported by CPE, the port can be activated only by the G.lite standard.

G992.5According to the mode supported by CPE, the port can be activated only by the G.dmt.bisplus standard.


Rate Parameters

Minimum transmit rate: It presents the minimum activation rate required in the current direction

after the line activation.

Maximum transmit rate: It presents the maximum activation rate in the current direction after the

line activation. If the rate is fixed, the maximum and the minimum activation rates must be

identical.

After the activation, the actual line rate will satisfy the activation requirement after being adapted

from the expected maximum rate to the minimum rate. Such an activation requires that the error

bit rate must be smaller than 10-7, and the noise margin must be around the target noise margin.

During the ADSL connecting, if the line is in good conditions, and the calculated downstream

rate is bigger than the configured maximum rate, the system will restrict the downstream rate to

the maximum rate and increase the downstream SNR margin. If the line is in poor conditions, and

the calculated maximum downstream rate cannot satisfy the configured maximum value, the

system will set up the connection at the actual downstream rate on the premise of guaranteeing

the target downstream SNR margin.

Configure the upstream rate and the downstream rate in the same way.

Will you set parameters for rate? (y/n)[n]:Y


Low Upstream Rate Affecting Downstream Rate

[Fault Description]The upstream rate is configured too low and causes the low downstream rate.

[Troubleshooting]Check the port parameter, and it is found that the upstream rate of the ADSL port on the MA5100 is 64 kbps, and the downstream rate is 960 kbps. Change the upstream rate to 512 kbps, and the fault is troubleshot.

[Fault Analysis]As charging is involved, the downstream rate and the upstream rate differ greatly. In application, however, if the upstream rate is lower than 128 kbps, such as 64 kbps, the downstream rate will be affected seriously.

[Cause Analysis]If an ADSL modem connects a large number of LAN subscribers, or the subscriber uses many Internet services, a lot of TCP sessions will occur. In this case, a multiple of TCP receivers send the ACK message at a time and causes the upstream congestion or delay. As a result, the transmitter resends the TCP packet, and the actual downstream rate is low. Therefore, it is recommended not to set the upstream rate to be lower than 128 kbps.


Upstream/Downstream Channel Bit Swap

The bit swap function supports the bit distribution or the power adjustment between

subbands without line activation.

During the line activation, SNR and the bit allocation are calculated independently for each

subband. After the line activation, the line SNR may change for the external environment

account. Therefore, the line SNR change may be represented as that SNR increases on

some subbands and decreases on some others. If the state persists for a long time, the bit

error rate of the line may increase, or cannot satisfy the activation rate and requires the line to

negotiate again. If a subband SNR decreases too much and the subband cannot carry the

allocated bits, the bit swap functions to shift some bits of the subband to other subbands of

high SNR for bit swapping, such as the upstream/downstream channel bit swap.

Configure the bit swap as follows:

> Downstream channel bit swap 0-disable 1-enable (0–1) [1]:

> Upstream channel bit swap 0-disable 1-enable (0–1) [1]:


Trellis Coding

Trellis coding works out the best coding gain using a special coding calculation to

increase the line SNR gain. The practice proves that using trellis coding can increase

the line SNR gain by 3–6 dB at least, but the portion of the error control redundancy

code in the line bandwidth does not increase. The improvement is represented as that

the activation rate increases a lot compared with that in its failure case after the trellis

coding switch is enabled. According to the ADSL standard (G.992.1), the trellis coding function is optional. At

present, all Huawei ADSL board series support this function. In the ADSL2/ADSL2+

standard (G.992.3/G.992.5), the trellis coding function is forcibly supported. Now,

Huawei ADSL2+ board series also support this function.

Enable or Disable the trellis function as follows:

> Trellions mode 0-disable 1-enable (0–1) [1]:


Channel Mode

There are two channel modes: interleaved mode and fast mode. • Fast mode: This mode has short delay and general error correction capability. So it applies to the delay-sensitive service.• Interleaved mode: This mode can solve the burst noise and has a good capability of correcting errors. The deeper the interleaved depth is, the better the error correction capability is, and also the longer the delay is. Therefore, the interleaved mode applies to the delay-insensitive service that requires low reliability.

Unit of interleaved delay• DMT: Use the depth as its unit directly, namely, the interleaved depth. • MS: Use millisecond (ms) as its unit, namely, the interleaved delay. Choose the channel mode: > Please select channel mode 0-interleaved 1-fast (0–1) [0]:


Interleaving Principle

21 20 19 18 17 16 15

14 13 12 11 10 9 8

7 6 5 4 3 2 1

21 20 19 18 17 16 15

14 13 12 11 10 9 8

7 6 5 4 3 2 1

Enter the data from FEC

Read the data to channels

Interleaving process

De-interleaving process

save the data through channels

Read the data to FEC

Depth D=3

Span N=7

21……6, 5, 4, 3, 2, 1

……16, 9, 2, 15, 8, 1

21……6, 5, 4, 3, 2, 1

Object 1

Object 2

17

17

13

17

18

18

20

18

19

19

7

19

16

16

6

16

20

20

14

20

21×1413121110×876543×1

211514131211109876×××21Receiving bit

(no interleaving)

×××

2119125181141710316921581Bit order

(interleaving)

21151413121110987654321

17

17

13

17

18

18

20

18

19

19

7

19

16

16

6

16

20

20

14

20

21X1413121110X876543X1

211514131211109876XXX21

XXXBurst error

2119125181141710316921581

21151413121110987654321Bit order

(no interleaving)

Receiving bit(interleaving)


Improper Interleaved Depth Causing a Fault

[Fault Description] The ADSL subscriber (PPPoEoA) on the MA5100 accesses the Internet after being authenticated on the

ISN8850. After the service is available, subscribers complain that they are often offline but can dialup to be online soon after the fault.

[Troubleshooting]1. By monitoring the end-user terminal, we found that the fault occurs, meanwhile, the modem is not deactivated. 2. Partial user terminals use the networking modem+HUB+PC. Therefore, we presume that the HUB is blocked

when a lot of data are switched due to the HUB performance. We replace the HUB, but the fault persists. 3. The fault may be traced to that the CPU utilization of the ISN8850 is too high. By checking, we found that the

CPU utilization is only 19%. It indicates that some other problems cause the fault. 4. After excluding the two possibilities, check the data configured on the MA5100. we found that the port works in

the interleaved mode and with the interleaved depth as 64. During monitoring the user terminal, we found that the PING packet jitters regularly. Namely, a PING packet of long delay occurs every seven/eight stable PING packets. In the PPPoEoA mode, the ISN8850 sends the PPP ECHO packets to the client software every 40 seconds to detect whether the PPP subscriber is online. If the ISN8850 has sent such a packet for three times (two minutes) and got no response, it will disconnect the subscriber. Therefore, the fault may be traced to that the interleaved depth is too big and causes the PPP ECHO packet sent by the ISN8850 lost, and the ISN8850 disconnects the subscriber. After the check and analysis, we change the interleaved depth parameter of the port to 16, the condition is improved. Change the parameter to 8, and the fault is troubleshot.

[Causes Analysis] Too deep interleaved depth causes long delay on network, furthermore, some data lost and the ISN8850

disconnects the subscriber.


SNR/Noise Margin

The SNR margin refers to the additional noise that the system can tolerate on the premise

of guaranteeing the current rate and error bit rate. The SNR margin of the modem and the

stability of the ADSL connection are in direct ration. Generally, the bigger the SNR margin

of modem is, the more stable the connection is. Meanwhile, the SNR margin and the

activated physical connection rate are in inverse ratio. Namely, the bigger the SNR margin

is, the lower the activated physical connection rate is.

Target SNR Margin: It refers to the required noise margin for initialization when the bit error

rate equal to or smaller than 10-7.

Maximum SNR Margin: When the noise margin exceeds this value, ADSL must lower its

output power.

Minimum SNR Margin: When the noise margin is smaller than this value, ADSL must

promote its output power. If the promotion fails, ADSL should perform the negotiation

again.

Set the SNR margin of modem as follows:

> Will you set SNR margin for modem? (y/n)[n]:y


Signal Attenuation

SATN refers to the signal attenuation. The SATN value is the ratio of the received

signal power at the receive end to the transmitted signal power at the transmit

end. In fact, SATN is the line attenuation parameter in ADSL, ranging from 0

to 102.2 dB with the step as 0.1 dB.

If the signal attenuates too much, the ADSL service will be unstable and

deactivated frequently. SATN can be caused by the following factors:

• Crosstalk

• Bridge connector reflection

• Line connector attenuation

• Line resistance attenuation


Locating the Line Fault Based on Channel Attenuation

[Fault Description]The ADSL Internet service of an office is faulty. Several ports are frequently deactivated at the interval of

several hours, or sometimes the ports are deactivated automatically because of the line fault several times every hour. The subscriber connecting to these ports are less than 500 m away from the MA5100.

[Troubleshooting]1. Run the related port command, and the channel attenuation is found to be too big on these port. The

channel attenuation of some of the ports is 24 dB upstream and 22 dB downstream, and that of some other ports is 42 dB upstream and 20 dB downstream.

2. The parameter shows that the line connection is abnormal. Punching the wire down on MDF, and connect the telephone wire again in the connection box. In this case, the line attenuation decreases to a small value (less than 10 dB). After a test, it is found that the stability of subscriber connection is promoted. The subscribers are offline only for once or twice within two days.

[Cause Analysis]The channel attenuation and the distance between RTU and the MA5100 are in direct ratio but without the

simple linear relation. Nevertheless, if the distance increases by 100 m, the attenuation increases by 2 dB. In this faulty case, the subscriber is less than 500 m away from the MA5100, thus the attenuation must be small in theory. But the attenuation is big in fact, it indicates that the signal attenuates at the connection point but not on the copper wire. Therefore, during enabling the ADSL service, judge the line connection status by checking the channel attenuation. If the actual attenuation is bigger than the estimated one, the line is faulty because of either the non-standard cable or the poor connection of the connector (this case occurs at the subscriber connection box and on MDF most of the time). Following this way to locate the fault, improve the line condition and connection stability.


Parameter Reference Table

Downstream Upstream

Line Length Noise Margin Attenuation Rate Noise Margin Attenuation Rate

0 7 5.5 27232 7 9 1088

1000 6 9.5 25184 6 1.5 1120

2150 7 20 20832 7 23.5 1024

3050 7 30 9056 7 41.5 1056

4000 7 39 5472 7 54 992

5200 8 45.5 2496 7 63.5 896

6100 9 53.5 960 6 63.5 672

7000 12 61 192 6 63.5 416

The following table lists the test parameter value by using the MT880 (target noise margin is 6). The table gives only the reference value of the line length, noise margin, attenuation and rate. The result of the actual line test is a little worse than the values.


This chapter describes the key parameters of the line profile and their

meanings. During configuring the line profile, inherit the default

value for most parameters. What requires change are the following

parameters: the activation standards used by the line profile,

interleaved/fast mode, upstream/downstream activation rate range.

Summary Summary


Questions

1. What is the interleaved mode? Please describe the relation between the

interleaved depth and delay.

2. Which does the negotiation begin with, the high-rate mode G.992.5 or

the low-rate mode G.992.1 if CO (full compatible ) and CPE (full

compatible) work in the negotiation mode?





Chapter 4 ADSL TrendChapter 4 ADSL Trend


Three ADSL Problems

At present, ADSL often meets the following three problems: • Subscribers are offline exceptionally.• Subscribers access Internet at a low rate.• Subscriber accounts are stolen.

Exceptional offline fault is usually traced to either of the following causes: • PPP connection is faulty because of the loss of the Keep Alive packets that are based on the PPP

connection. • Subscribers are offline forcibly because of the Radius packet loss.

Low rate for the access to Internet refers to that the port rate is not qualified to guarantee the

promised rate. According to the survey, the low rate is often caused by the poor line quality and the

unreasonable network architecture on access network.

If the subscriber account is shared, the account is stolen and the illegal subscriber is difficult to

track. This fault is traced to that telecom carriers do not limit and protect the broadband subscriber

account because they lack an effective mechanism to identify subscribers uniquely.


ADSL Trend

Broadband

ADSL ADSL2 ADSL2+ VDSL2+

Full-service

Support the IPTV, Triple Play, leased line, and some other

services.

Intelligent

Speed up the ADSL application, and locate the fault range

accurately to reduce the service interruption time.


Obtaining the Newest Documentation

The ADSL standardization begins with the regional standard, such as

T1E1.4 (North America) and ETSIM6 (Europe). Later, ITU takes charge of

the regional ADSL standardization. This organization is a leader of the

ADSL standardization.

www.itu.int/ITU-T/ International Telecommunications Union-

Telecommunications sector (ITU-T)

www.dslforum.org/ ADSL Forum

www.t1.org/t1e1 ANSI T1E1.4 (North America)


Thank You

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