ULAF Training Part 4

1
xDSL and optical network access
PRINCIPLES OF xDSL
2
Topics

• Line codes
• xDSL technologies
• HDSL reference configuration
• Line coding
• Principle of HDSL Transmission
• Cable section for HDSL
• Attainable distances

3
2Mbit/s transmission Line codes ? Reduction of
line speed (1)
1
0
0
1
0
0
0
AMI - Alternating Mark Inversion 2048 kbit/s f0
1024kbit/s (1966.)
1
1
0
0
0
1
0
0
1
HDB3 - High Density Bipolar 2048kbit/s f0
1024kbit/s (1970.)
1
0
artificial 1 after three 0s, which
violates the alternating mark inversion rule
3
2B1Q - HDSL 2 x 1168kbit/s ? 584kbaud per UTP ?
f0 292kHz
1
1
0
0V
-1
2B four binary values
-3
1Q one bit with four levels
4
2Mbit/s transmission Line codes Reduction of
line speed (2)
TC - PAM16 Trellis Coded - Pulse Amplitude
Modulated line code with 16 levels for SHDSL
(4B1HEX)
8 levels
1
0
1
1
0V
four bits with sixteen values e.g.
2320kbit/s ? 580kbaud per UTP ? f0 290kHz
4B
- 8 levels
Trellis code is used to avoid the transitions
between values with small level differences
one bit with sixteen levels 1HEX
5
xDSL

• The idea of DSL to attain longer transmission
  distances without regenerators using different
  line codes for line speed reductions
• Old 2Mbit/s transmission using HDB3 line code -
  bipolar signal with the main frequency
  f01024kHz directions separated into two wire
  pairs regenerator distances 1,8 to 2,4 km
• HDSL/SDSL line code 2B1Q (4PAM) or CAP
  (Carrierless Amplitude and Phase Modulation)
  splitting of 2Mbit/s signal into two or three
  wire pairs or no splitting at all (SDSL) both
  directions in the same wire pair using echo
  cancellation main frequencies for example 292kHz
  for two wires (1168kbit/s) or 580kHz
  (2320kbit/s) for SDSL
• SHDSL line code 16PAM (4B1HEX) brings the
  further line speed reduction - e.g. 290kHz
  (2320kbit/s) for one wire pair echo
  cancellation new feature - settable line speed
  from 192kbit/s to 2320kbit/s in 64kbit/s steps to
  get longer distances without regenerators

6
Tutorial on xDSL technologies
http//www.etsi.org/technicalactiv/xdsl_tutorial.h
tm
7
ETSI TS 101 135 - Reference configuration
A fully equipped HDSL CORE consists of one, two
or three HDSL transceiver, REG, DLL combinations
depending on data transmission rate.
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ETSI TS 101 135 - Framing procedures
9
HDSL Line coding 2B1Q and CAP
CAP - Carrierless Amplitude and Phase Modulation
2B1Q - 2 Binary 1 Quaternary
10
HDSL Comparison between 2B1Q and CAP
Performance with noise 2B1Q has better
performance measured with ETSI 0dbm noise
(complicated Trellis coding with Tomlison
precoding brings no advantages for CAP under real
noise conditions) Performance without noise CAP
offers a better performance than 2B1Q under low
noise and laboratory conditions CAP causes more
crosstalk disturbances in cables due to 1-2 dB
higher transmitting levels compared with HDSL
systems based on 2B1Q
11
Principle of HDSL or SHDSL transmission
or TC - 4B1HEX (16PAM)
or 192 to 2304kbit/s for SHDSl
or 1HEX - 4B
Remark HDSL circuit for one twisted wire pair.
For 2Mbit/s two wire pairs are necessary using
equipment with data rate 1168kbit/s per wire
pair. For SHDSL the bit rates are from 192 to
2304kbit/s via one UTP.
12
Preparation of cable section for xDSL
HDSL transceiver is not properly connected
a
a
The wires do not belong to the same pair.
There exist "bridged taps" - forgotten lines at
MDF which cause reflections
13
Cable section attenuation
Range 265 to 315 kHz (? 25 kHz from the main
frequency of HDSL signal - f0 292 kHz)
Zgen Zrec 135 ? or 150 ?
Requirements a1lt 37 dB including all resonant
maxima (standing waves) a2lt 27 dB at 150 kHz
(ETSI TS 101 135)
14
Cable section noise
This measurement is important because of possible
crosstalk disturbances from neighbour quads and
wire pairs.
line termination
Noise receiver
Zterm Zrec 135 ? or 150 ?
Broadband noise up to ? 1,5 MHz n lt 10
mVrms Selective peaks 10 kHz to 1,5 MHz n lt 10
mVpp
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HDSL Attainable distances on ETSI cable types
The transmission range is dependent on the
diameter, capacity and other characteristics of
the copper cable, as well as on the level of
interferences in its environment.
16
HDSL Attainable distances on non-ETSI cable types
Conditions Cable section attenuation at 150 kHz
27 dB broadband noise up to 1.5 MHz lt 10
mVrms
17
Abbreviations
OF Optical fibre OTU Optical termination
unit PBX Private branch exchange PCB Printed
Circuit Board PRA ISDN-primary rate access
PoP Point of Presence REG Regenerator for
HDSL RPS Remote power supply for
HDSL SHDSL Single pair digital subscriber
line STU SDSL termination unit TCM Time
Compression Multiplex TMN Telecommunication
management network ULAF Universal line equipment
access family UTP Unshielded twisted wire
pair V.xx Data interface X.21 Data
interface WAN Wide area network 2B1Q Line code
for HDSL transmission 16PAM Line code for SHDSL
transmission
DCN Data communication network DCE Data
communication equipment DTE Data terminal
equipment EOC Embedded operating
channel ETSI European telecommunication standard
institute G.703 ITU-T recommendation G.704 ITU-T
recommendation HDSL High-bit-rate digital
subscriber line HTU HDSL termination
unit ISDN Integrated services digital
network LAN Local area network LCT Local craft
terminal LL Leased lines LT Line
termination MUX Multiplexer NMS Network
management system NT Network termination OMI Opera
tions maintenance interface unit