ADSL technology Access Networks lectures 2008/09.
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Transcript of ADSL technology Access Networks lectures 2008/09.
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ADSLADSL technology technology
Access NetworksAccess Networks
lectureslectures 2008/09 2008/09
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... once more...
Broadband Network (Internet)
Wiring Distribution Frame) Customer
Premises Wiring
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= 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
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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
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POTS Upstream Downstream
Fig. ADSL spectrum in frequency multiplex
Frequency
POTS Upstream Downstream
Frequency
Fig. ADSL spectrum with echo compensation
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ADSL and ISDN
Upstream Downstream
Frequency
Frequency
Frequency
Basic Access (4B3T link code)
Basic Access (2B1Q link code)
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ADSL
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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) )
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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
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Splitter
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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
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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
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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+
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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 (!)
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• 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)
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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.