ADSL Protocol Basics ISSUE1.0-20060630-A

HUAWEI TECHNOLOGIES CO., LTD. For internal use only Page 1

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/ADSL2/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 Symmetrical 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/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




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%.




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/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 2 ADSL/ADSL/ADSL2+ Principles

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.

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

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







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]:


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


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 2 ADSL/ADSL/ADSL2+ Principles


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

www.huawei.com

Date post:	26-Dec-2015
Category:	Documents
Upload:	moayad-mahamead
View:	13 times
Download:	1 times

ADSL Protocol Basics ISSUE1.0-20060630-A

Documents