adsl technology access networks lectures 2008/09
TRANSCRIPT
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.