Transcript Technológia ADSL

ADSL technology
Access Networks
lectures 2008/09
Broadband
Network
(Internet)
Wiring
Distribution
Frame)
... once more...
Customer
Premises
Wiring
ADSL
= 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)
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
ISDN-BRA
Frequency
Analog
teleph.signal
Fig. 1 ADSL spectrum with various variants [2]
ADSL
variant
number of
subchannels
from
to
only data
Tab.1 Comparison of ADSL variants
speed
number of
subchannels
from
to
speed
POTS
Downstream
Upstream
Frequency
Fig. ADSL spectrum in frequency multiplex
POTS
Upstream
Downstream
Frequency
Fig. ADSL spectrum with echo compensation
ADSL and ISDN
Upstream
Downstream
Frequency
Basic Access (4B3T link code)
Frequency
Basic Access (2B1Q link code)
Frequency
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].
S

C  B log 2 1  
 N
[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) )
LF
symmetrical pair
HF
Fig.2 Typical termination of ADSL line on the user side
Fig.3 ADSL line configuration with splitters
user
Provider
user line
Data network
ATU-C = ADSL transceiver unit at the central office,
ATU-R .....at the Remote home or business
Splitter
filtre DP a HP
ATU-C (ATU-R) =ADSL Transceiver Unit (on the user side)
koncentrator and/or switch (switching array)
multiplexor/demultiplex.
PHY = physical interface
Fig.4 Reference model of ADSL in comparison to general xDSL model [6]
transmitt
ed data
bit sequence securing
scrambler
trellis coder
carrier mapping
RS coder
CP
adding
D/A
conversion
data
interface
analog
section
Echo
cancelling
received
data
A/D
conversion
dig.QAM
power
spreading
analog
transmit.part
line
hybrid
analog
receiver part
secured bit sequence decoding
Fig.5 Functional scheme of ADSL modem (and steps of data treatment …)
ADSL2+
2,2 MHz
1,1 MHz
Up to 18,000 feet (5.5 km)
Up to 25 Mbps down
Up to 1 Mbps Upstream
Fig.6 ADSL 2+ system
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.transmission
transmission 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.