Transcript Intro to xDSL Part 3

Introduction
to
xDSL
Part III
Yaakov J. Stein
Chief Scientist
RAD Data Communications
Stein Intro xDSL 3.1
Introduction to xDSL
I Background
history, theoretical limitations, applications
II Modems
line codes, duplexing, equalization,
error correcting codes, trellis codes
III xDSL - What is x?
x=I,A,S,V - specific DSL technologies
competitive technologies
Stein Intro xDSL 3.2
Quick recap
Lecture 1
How did we get to where we want to go?
How far can we go?
Lecture 2
How can we get there?
Lecture 3
How can we get there?
What do we do when we get there?
Stein Intro xDSL 3.3
Quick Review
DSL leaves concept of using 4KHz analog line
Use UTP as general transmission line
Rate limited by






line loss
thermal noise
NEXT crosstalk
FEXT crosstalk
RF ingress (AM broadcast, ham, etc.)
misc (splices, bridged taps, echo, filters, sync)
Stein Intro xDSL 3.4
Introduction to xDSL III
Applications
Deployment topologies
IDSL
HDSL, HDSL2, SDSL
ADSL, G.lite
VDSL
competitors (cable modems,wireless)
HPNA
Stein Intro xDSL 3.5
The Baby Bells had a problem ...
1993: cable TV companies started offering
10 Mbps Internet access
Internet seen as potential future market
RBOC’s Plan: HFC to every home by 1996!
This didn’t happen




costs grew
regulatory problems
no standardization
LEC’s had lower operating expenses
What could be done?
Stein Intro xDSL 3.6
Telco Alternatives
Fiber, coax, HFC
COST: $10K-$20K / mile
TIME: months to install
T1
COST: >$5K/mile for conditioning
TIME: weeks to install
DSL
COST: @ 0 (just equipment price)
TIME: @ 0 (just setup time)
Stein Intro xDSL 3.7
Analog (or V.90) modems
CO SWITCH
PSTN
UTP subscriber line
modem
CO SWITCH
modem
network/
ISP
router
Stein Intro xDSL 3.8
xDSL System Reference Model
CO SWITCH
PSTN
POTS-C
network/
ISP
router
Analog
modem
WAN
POTS
SPLITTER
POTS-R
UTP
POTS
SPLITTER
DSLAM
xTU-C
PDN
xTU-R
x = H, A, V, ...
Stein Intro xDSL 3.9
VoDSL
CO SWITCH
PSTN
POTS-C
network/
ISP
router
POTS
SPLITTER
WAN
DSLAM
xTU-C
POTS-R
UTP
POTS
SPLITTER
PDN
xTU-R
Stein Intro xDSL 3.10
Network Reference Model
PDN (Premises Distribution Network) is ethernet or USB
WAN is typically ATM or FDDI (even though FDDI is LAN protocol)
Internet is TCP/IP
HDSL connects to DACS and to CSU
Many interconnect possibilities (may impact modem design)
full STM, full ATM, full packet network, packet-ATM-packet, etc.
Example, FR WAN, ATM over UTP, Ethenet PDN
Modems should be cell pumps, not bit pumps
(also need CIF protocol to tunnel ATM through Ethernet)
Stein Intro xDSL 3.11
Splitter
Splitter separates POTS from DSL signals



Must guarantee lifeline POTS services!
Hence usually passive filter
Must block impulse noise (e.g. ring) from phone into DSL
ADSLforum/T1E1.4 specify that splitter be separate from modem
No interface specification yet (can’t buy splitter and modem from different vendors)
Splitter requires installation
 Costly technician visit is the major impediment to deployment
 G.lite is splitterless ADSL
Stein Intro xDSL 3.12
xDSL - Maximum Reach
Stein Intro xDSL 3.13
Examples of Realistic Reach
More realistical design goals (splices, some xtalk)

1.5 Mbps 18 Kft
5.5 Km
(80% US loops)

2 Mbps
16 Kft
5 Km

6 Mbps
12 Kft
3.5 Km

10 Mbps
7 Kft
2Km

13 Mbps
4.5 Kft
1.4 Km

26 Mbps
3 Kft
900 m

52 Mbps
1 Kft
300 m (SONET
(CSA 50% US loops)
STS-1 = 1/3 STM-1)
Stein Intro xDSL 3.14
xDSL flavors
modem
speed
reach
main applications
IDSL
160 (144) Kbps
5.5 km
HDSL
2 Mbps (4-6W)
3.6-4.5 km
HDSL2
2 Mbps (2W)
3 km
POTS
replacement,
videoconferencing,
Internet access
T1/E1 replacement
PBX interconnect,
FR
same as HDSL
SDSL
<= 2 Mbps
3 km
same as HDSL
Stein Intro xDSL 3.15
xDSL flavors
modem
speed
reach
main applications
ADSL
8 Mbps DS
3.5-5.5 km
residential Internet,
video-on-demand
G.lite
1 Mbps DS
5.5 km
Internet access,
VoIP
VDSL
<= 52 Mbps
300m - 1 km
cable modem
10-30Mbps DS
shared
50 km
LAN interconnect,
HDTV,
combined services
residential Internet
HPNA
1, 10 Mbps
home wiring
residential
networking
Stein Intro xDSL 3.16
ITU G.99x standards

G.991 HDSL (G.991.1 HDSL

G.992 ADSL (G.992.1 full rate

G.993 VDSL

G.994 HANDSHAKE

G.995 GENERAL (INFO)

G.996 TEST

G.997 PLOAM

G.998 PNT (HPNA)
G.991.2 SHDSL)
G.992.2 G.lite G.992.3,4,5 new)
Stein Intro xDSL 3.17
PSD(dBm/Hz)
Some xDSL PSDs
T1
IDSL HDSL HDSL2
ADSL
F(MHz)
Stein Intro xDSL 3.18
Line Codes
PAM
 IDSL, HDSL (2B1Q)
 HDSL2 (with TCM and optionally OPTIS)
 SDSL
QAM/CAP

proprietary HDSL/ADSL/VDSL
DMT


ADSL
G.lite
VDSL line code war is still raging (but QAM seems to be winning)
Stein Intro xDSL 3.19
T1/E1
DS1 rate
1 bit per symbol AMI
Half duplex on each UTP
Full duplex requires 2 UTP (4W)
Simple DSP
Linear equalization
Needs conditioning
Repeaters (every km)
Stein Intro xDSL 3.20
IDSL
Original DSL (1980s)
160 Kbps in 80 KHz BW
resistance design reach (18Kft)
popular in Europe, but not US
2 bit PAM called 2B1Q (2 Bits in 1 Quat)
+3
+1
-1
10 +3 (Gray code)
11 +1
01 -1
-3
00 -3
alternative line code:
4B3T (4 Bits in 3 Ternary symbols)
Stein Intro xDSL 3.21
HDSL
Replace T1/E1 DS1 service
Use 2B1Q line code, DFE
Full duplex on each pair with echo cancellation
Full CSA without conditioning/repeaters
more complex DSP (250 MIPS)
ANSI: 2 pairs for T1 (each 784 Kbps)
ETSI: 1, 2, 3 or 4 pairs
Most mature of DSL technologies
Stein Intro xDSL 3.22
HDSL vs T1(AMI)
T1
HDSL
Stein Intro xDSL 3.23
HDSL - continued
HDSL is repeaterless T1/E1
Major application - multiline POTS
Reach is CSA (less than ADSL!)
Can add doublers to extend range
Other applications:

PBX extension

digital local loop

campus networks

Internet
Stein Intro xDSL 3.24
HDSL2, SDSL, SHDSL, OPTIS
Customers request HDSL service that is
 single UTP HDSL
 at least full CSA reach
 spectrally compatible w/
HDSL, T1, ADSL, etc.
Variously called
HDSL2 (ANSI)
SDSL Symmetric DSL (ETSI)
SHDSL Single pair HDSL (ITU)
This is the DS1 service that will last!
Stein Intro xDSL 3.25
OPTIS Overlapping PAM Transmission with Interlocking Spectra
A solution that achieves these goals
16 level PAM with 517K baud rate
very strong (512 state, >5 dB) TCM
1D for low (216 msec) latency (speech)
strong DFE
tailored spectra (fits between HDSL and T1)
partially overlapped (interlocking) spectra
folding (around fb/2) enhances SNR!
upstream bump for spectral compatibility
Stein Intro xDSL 3.26
OPTIS - continued
Stein Intro xDSL 3.27
OPTIS - continued
Stein Intro xDSL 3.28
ADSL
Asymmetric - high rate DS lower rate US
Originally designed for video on demand
Almost retired due to lack of interest
…but then came the Internet
Studies show DS:US should be about 10:1
full rate ADSL 512-640 kbps US, 6-8 Mbps DS G.lite 512 Kbps US, 1.5 Mbps DS
ADSL could mean All Data Subscribers Living
Stein Intro xDSL 3.29
Why asymmetry?
NEXT is the worst interferer stops HDSL from achieving higher rates
FEXT much less (attenuated by line)
FDD eliminates NEXT
All modems must transmit in the SAME direction
A reversal would bring all ADSL modems down
Upstream(US) at lower frequencies and power density
Downstream (DS) at high frequencies and power
Stein Intro xDSL 3.30
Why asymmetry? - continued
PSD (dBm/Hz)
US
DS
F(MHz)
Stein Intro xDSL 3.31
Echo cancelled ADSL
FDD gives sweet low frequencies to US only
and the sharp filters enhance ISI
By overlapping DS on US
we can use low frequencies and so increase reach
Power spectral density chart
Stein Intro xDSL 3.32
ADSL - continued
ADSL system design criterion BER 10-12
(1 error every 2 days at 6 Mbps)
Raw modem can not attain this low a BER!
For video on demand:
 RS and interleaving can deliver (error bursts of 500 msec)
 but add 17 msec delay
For Internet:
 TCP can deliver
 high raw delay problematic
So standard defines TWO framers
fast (noninterleaved ) and slow (interleaved) buffers
Stein Intro xDSL 3.33
ADSL standard
ITU (G.dmt) G.992.1, ANSI T1.413i2 standard
First ADSL data implementations were CAP
Standard is DMT
DMT allows approaching water pouring capacity
DMT is robust
DMT requires more complex processing
DMT may require more power
Stein Intro xDSL 3.34
DMT
Discrete Multitone is a form of FDM (Frequency Domain Multiplexing)
Discrete Multitone is a form of MCM (MultiCarrier Modulation)
It uses many different carriers, each modulated QAM
Each tone is narrow


low baud rate (long frame)
channel characteristics are constant over tone
Number of bits per tone chosen according to water pouring
Put more bits where SNR is good
Stein Intro xDSL 3.35
DMT - continued
DMT is OFDM (Orthogonalized FDM)



Carrier spacing is precisely baud rate
Center of tone is precisely the zero of all other sincs
ICI minimized
ISI minimized by having a long interframe guard time
DMT modem can be efficiently implemented using FFT
DFT is mathematically equivalent to a bank of filters
Filtering is equivalent to cyclic convolution
So use cyclic prefix rather than guard time
Stein Intro xDSL 3.36
DMT - continued
frequency
time
Stein Intro xDSL 3.37
ADSL DMT
Baud rate (and channel spacing) is 4.3125 KHz
US uses tones 8 - 32 (below 30 KHz reserved)
DS uses 256 tones (FDM from tone 33, EC from tone 8)
P
O
T
S
US
8
DS
32
256
Stein Intro xDSL 3.38
DMT misc.
bit handling ((de)framer, CRC, (de)scrambler, RS, (de)interleaver)
tone handling (bit load, gain scaling, tone ordering, bit swapping)
QAM modem (symbolizer, slicer)
signal handling (cyclic prefix insertion/deletion, (I)FFT,
interpolation, PAR reduction)
synchronization (clock recovery)
channel handling
(probing and training, echo cancelling, FEQ, TEQ)
Stein Intro xDSL 3.39
RADSL
Rate Adaptive ADSL

Not variable rate (not small fast variations)

Increases percentage of useable lines

Fine for Internet access
but not for video on demand

Standard ADSL supports 32Kbps steps
RADSL provides management protocols
Stein Intro xDSL 3.40
G.lite
ITU (G.lite) G.992.2, UAWG
ADSL compatible DMT compatible using only 128 tones
512 Kbps US / 1.5 Mbps DS
Still much faster than V.34 or V.90 modems
No splitter required!
Certain features removed for simplicity
simpler implementation (only 500 MIPS < 2000 MIPS for full rate)
Stein Intro xDSL 3.41
New ADSLs
ITU has continued development of G.dmt.bis, G.lite.bis
Should become G.992.3, G.992.4, G.992.5
ADSL2
Longer reach with higher rate (1.5 Km @ 12 Mbps)
4D 16-TCM constellations, Stronger RS FEC
Lower framing overhead (programmable 4-32Kbps overhead)
Power cutback standby mode
Algo improvements (e.g. real-time tone re-ordering, relocatable pilot tone)
ADSL+
Uses more BW for higher bitrates for short reaches
double BW (512 bins) - double speed (24 Mbps!)
Annex J
Symmetric 3 Mbps
Stein Intro xDSL 3.42
VDSL
Optical network expanding (getting closer to subscriber)
Optical Network Unit ONU at curb or basement cabinet
FTTC (curb), FTTB (building)
These scenarios usually dictates low power
Rates can be very high since required reach is minimal!
Proposed standard has multiple rates and reaches
Stein Intro xDSL 3.43
VDSL - rate goals
Symmetric rates
6.5 4.5Kft (1.4 Km)
13
3 Kft (900 m)
26
1 Kft (300 m)
Asymmetric rates (US/DS)
0.8/ 6.5
1.6/13
3.2/26
6.4/52
6 Kft
4.5 Kft
3 Kft
1 Kft
(1.8 Km)
(1.4Km)
(900 m)
(300 m)
Stein Intro xDSL 3.44
VDSL - Power issues
Basic template is -60 dBm/Hz from 1.1MHz to 20 MHz
Notches reduce certain frequencies to -80 dBm/Hz
Power boost on increase power to -50 dBm/Hz
Power back-off reduces VTU-R power so that won’t block another user
ADSL compatibility off use spectrum down to 300 KHz
Stein Intro xDSL 3.45
VDSL - duplexing
In Japan and campus applications can operate TDD (ping pong)
SDMT Synchronous DMT
(2 KHz frame can be heard in adjacent pairs or hearing aids)
Rest of world PSTN only FDD is allowed
Can divide US and DS into 2 areas (e.g. ADSL) or more
Need guard frequencies because of clock master/slave problems
Zipper - large number of interleaved frequency regions
(even on a bin by bin basis)
Stein Intro xDSL 3.46
VDSL line code wars
VDSL Alliance
DMT
VDSL Coalition
QAM
MORE
LESS
robust to noise
power
capacity
spectral compatibility
IPR
complex
expensive
A/D bits
With no complexity constraints probably equivalent
Stein Intro xDSL 3.47
T1E1.4 draft T1.424
T1E1.4 has released a 3-part “trial use” draft standard
 Part 1 Common Specifications
 Part 2 Single Carrier Modulation
 Part 3 Multicarrier Modulation
Objective tests have been specified (VDSL Olympics)
– Test definition may determine results
• SCM is NOT spectrally compatible with ADSL
• Present SCM implementations are more mature
– the tests should be of technology, not products
• MCM may be more robust in certain noise settings
The trials should be finished by July-August 2003
– ITU and IEEE are waiting for the results
Stein Intro xDSL 3.48
G.994.1 (G.hs)
Handshaking
Universal flexible method for initialization
Includes




tone negotiation for capability identification
common mode identification
exchange of nonstandard information
line probing (line code dependent)
Currently integral part of ADSL and G.lite
Anticipated that future ITU DSL modems will support as well
Stein Intro xDSL 3.49
G.997 (PLOAM)
Physical Layer Operation Administration and Maintenance
Includes
 physical layer management (SNMP based)
 configuration, fault and performance administration
 4 management interfaces
 optional OAM channel
 far end management
Currently integral part of G.992 (ADSL) family
Anticipated that future ITU DSL modems will support as well
Stein Intro xDSL 3.50
G.996.1 (G.test)
Universal testing procedure for xDSL modems
Finds margins in presence of
 POTS signaling
 impulse noise
 cross-talk from other services
 geographical position dependent test loops and wiring models
Currently integral part of G.992 (ADSL) family
Anticipated that future ITU DSL modems will support as well
Stein Intro xDSL 3.51
G.bond
ISDN defined BONDING of 2B channels to one 128Kbps line
G.991.2 (SHDSL) Annex E has physical layer bonding
ITU G.bond objectives:
1) be higher layer agnostic
2) be backward compatible with the present 2-wire G.shdsl Annex E solution
3) different rates on different pairs
4) be applicable to all DSL families, not just SHDSL
5) have low latency and overhead (to support TDM)
6) support dynamic addition and removal of pairs
If succeeds no need for layer 2+ aggregation protocols
(ATM-IMA, MLFR, MLPPP, 802.3ad etc) with
high overhead, high latency, same rates for each pair,
no dynamic addition/deletion support, etc.
Stein Intro xDSL 3.52
cVoDSL
Standard VoDSL sends TDM over ATM layer
Channelized VoDSL reserves N 64Kbps channels (N=1..4)
PRO Implemented on-chip (no GW), higher voice quality, lower delay
CON Consumes BW even if not used
VoIP
VoATM
cVoDSL
POTS
IP layer
AAL1
AAL2
ATM layer
AAL5
DSL physical layer
baseband physical layer
Stein Intro xDSL 3.53
Competitors
and
non-DSL
technologies
Stein Intro xDSL 3.54
G.998 (G.pnt,HPNA)

Studies show that about 50% of US homes have a PC
30% have Internet access, 20% have more than one PC!

Average consumer has trouble with cabling
HomePNA de facto industry standard for home networking




Computers, peripherals interconnect (and connect to Internet?)
using internal phone wiring (user side of splitter)
Does not interrupt lifeline POTS services
Does not require costly or messy LAN wiring of the home
Presently 1 Mbps, soon 10 Mbps, eventually 100 Mbps!
Stein Intro xDSL 3.55
HPNA

HPNA 1.0 (98Q3) has average data rate 1.0432 Mbps

Line code is PPM (pulse position modulation)
Each pulse is 4 cycles at 7.5 MHz (shaped)
time between pulses 3.27 msec < t < 6.07 msec
Can co-exist with full-rate ADSL and G.lite







HPNA 2.0 (ITU G.pnt) 10 - 32 Mbps
QAM line code
HPNA 3.0 up to 100 Mbps
Specification not yet finalized
Stein Intro xDSL 3.56
Cable modems
CABLE
MODEM
CMTS
CATV
HEADEND
fiber
OPTICAL
FIBER
CABLE
coax
COAXIAL
MODEM
AMPLIFIER
NODE
CABLE
MODEM
CABLE
MODEM
Stein Intro xDSL 3.57
Cable modems - continued
Line Code (nonstandard, IEEE 802.14)

QPSK/16 QAM US 1.5 Mbps (raw)

64/256 QAM DS

QPSK control channel
30 Mbps (raw)
FDD (US low frequencies, DS high frequencies)
BW to CM is shared
Performance degrades when too many users
Stein Intro xDSL 3.58
Cable modems - continued
DOCSIS - Data Over Cable System Interface Specification

Evolving specification for high-speed data-over-cable systems

DOCSIS 1.0 designed for transparent bi-directional IP traffic
– 3.2 MHz channel, 5.12 Mbps (QPSK)

DOCSIS 1.1 enhancement:
– 3.2 MHz channel, 10.24 Mbps (16-QAM)
– BW management features for QoS multimedia applications

DOCSIS 2.0 improved modem
– 6.4 MHz channel, 30.72 Mbps (64-QAM / 128-QAM+TCM / S-CDMA)
– symmetric upstream and downstream,
– increased noise immunity
Cable modems are not allowed to monitor each other
so Ethernet (CSMA/CD) is not possible
Stein Intro xDSL 3.59
MMDS
Wireless cable services are only minor competition

Services originated when telcos wanted to get into CATV
Multichannel Multipoint Distribution System (Wireless CATV)

2.6 GHz (SHF) frequencies

54 Mbps DS (33 uncompressed video/data channels)

Upstream traffic requires expensive subscriber transmitters

Line of site range

Technical problems: weather, trees
Stein Intro xDSL 3.60
LMDS
Local Multipoint Distribution System (Cellular TV)

28 GHz frequency

short-distance version of MMDS

uses small cells

small cell size requires many transmission antennas

most suitable for business LAN extension
Stein Intro xDSL 3.61
DBS
Direct Broadcast Satellite
Geosynchronous satellites already used for digital TV

POTS return connection

High powered transmitter return connection

Significant propagation delay
Low earth orbit (LEO) satellites

Minimal delays

Lower power uplink transmitters

Too expensive for residential use
Stein Intro xDSL 3.62