adsl technology access networks lectures 2008/09

ADSLADSL technology technology

Access NetworksAccess Networks

lectureslectures 2008/09 2008/09

... once more...

Broadband Network (Internet)

Wiring Distribution Frame) Customer

Premises Wiring

= Assymmetric Digital Subscriber Line

- inmodulation band (not baseband)

- ANSI standards (T1.413 of T1E1.4 group), ETSI (european requirement added to T1.413), ITU (groups of standards ITU-T G.991, 992, 995 etc. – they are downloadable from : ITU - publications – ITU-T)

ADSL

Specifications:• high bit rate transmission + telephone (and also analog) connection, or ISDN • max. downstream from 1,5 to 8 Mbps / max. upstream from 16 to 832 kbps (basic ADSL system) – various data speeds in dependence from user distance• freq.band up to 1,1 MHz, DMT modulation scheme (Discrete Multitone Transmission), max. 256 DMT channels, each is 4 kHz wide• for analog teleph.- lower 4 kHz, for ISDN up to 80 kHz (if there is ISDN transmission, the band for digital data is reduced)• reach - 5,5 km• frame transmission by means Cu- lines• Full / Lite versions

Analog teleph.signal

Frequency

Fig. 1 ADSL spectrum with various variants [2]

ADSL variant

number of subchannels

from to speed number of subchannels

speedfrom to

only data

Tab.1 Comparison of ADSL variants

ISDN-BRA

POTS Upstream Downstream

Fig. ADSL spectrum in frequency multiplex

Frequency

POTS Upstream Downstream

Frequency

Fig. ADSL spectrum with echo compensation

ADSL and ISDN

Upstream Downstream

Frequency

Frequency

Frequency

Basic Access (4B3T link code)

Basic Access (2B1Q link code)

ADSL

btw., relation between bandwidth and data speed:

Shannon-Hartley theorema for information capacity of channel with both digital signal with mean power S and additive Gauss noise with mean power N. Bandwidth of channel is B [Hz].

N

SBC 1log2 [bps] ... channel information capacity

B ... bandwidth [Hz]

S ...power of signal in the given band B [V2 or W]

N...power of noise in the given band B [V2 or W]

S/N . .. signal–to-noise ratio [-]

(we know already SNR[dB] =10 log (S/N) )

symmetrical pair

LF

HF

Fig.2 Typical termination of ADSL line on the user side

Fig.3 ADSL line configuration with splitters

user

Provider

Data network

user line

ATU-C = ADSL transceiver unit at the central office, ATU-R .....at the Remote home or business

Splitter

Fig.4 Reference model of ADSL in comparison to general xDSL model [6]

ATU-C (ATU-R) =ADSL Transceiver Unit (on the user side)

koncentrator and/or switch (switching array) multiplexor/demultiplex.

filtre DP a HP

PHY = physical interface

Fig.5 Functional scheme of ADSL modem (and steps of data treatment …)

data interface

transmitted data

scrambler RS coder

bit sequence securing

trellis codercarrier mapping

dig.QAMpower spreading

CP adding

D/A conversion

analog transmit.part

hybrid

lineanalog section

analog receiver part

A/D conversion

Echo cancelling

secured bit sequence decodingreceived data

Fig.6 ADSL 2+ system

2,2 MHz

1,1 MHz

Up to 18,000 feet (5.5 km)

Up to 25 Mbps down

Up to 1 Mbps Upstream

ADSL2+

ADSL2

- ITU-T G. 992.3, .4

- 2nd generation of ADSL standard

- downstream - up to 12 Mbps

- DMT modulation

- bandwidth - up to 2,2 MHz

- but: shorter reach (only from 1,5 to 2 km) !

- CVoDSL

ADSL2 + (fig.6)

- ITU-T G. 992.5

- downstream - up 24 Mbps

- bandwidth - up to 2,2 MHz (512 subchannels DMT, each 4kHz wide, up to 2,2 MHz)

- full data speed only in reach of max. 1,5 km from DSLAM (!)

• RE-ADSL = Reach Extended ADSL

-ITU-T G.992.3 – Annex L (it is annex to ADSL2 standard)

- optimalized DMT channels with the goal of larger length (manipulation with PSD of some channels their higher throughput

- dedicated to long lines (not for short ) – up to 5,5 km with the same date speed as in ADSL2

• RADSL = Rate Adaptive DSL- it is in development- both symetrical and assym.transmissiontransmission speed is adaptive (it depends on transmission conditions and distance)down 1-12 Mbps / up 128kbps-1Mbps DMT or CAP (and QAM) are supposed- for applications without synchronization requirements (IP services, ATM, Frame Relay)

• Bonded ADSL

- combines (bonds) 2 or more (up to 32) Cu-pairs for higher or extreme data speeds (for big and reach companies)

Literatúra

[1] Vaculík: Prístupové siete. ŽU v Žiline, 2000.

[2] J. Vodrážka: Přenosové systémy v přístupové síti. ČVUT, 2003.

[3] T. Anttalainen: Introduction to Telecom. Network Engineering, Norwood (USA - MA), 2003.

[4] L. Harte: Introduction to Digital Subscriber Line (DSL): Technologies, Operation and Systems. ALTHOS, 2005.

[5] ITU_T G.995.1 Recommendation, Geneva, 2001.