International Telecommunication Union
ITU-T xDSL Standards
Study Group 15 – Question 4
Stephen Palm Ph.D.
Principal Engineer
Broadcom
palm @ broadcom . com
ITU-T Workshop All Star Network Access
Geneva, 2-4 June 2004
Access Trend
ITU-T
V.34
V.90
G.961
ISDN
2004 June
Analog
Digital
Digital
Telco
Telco
Telco
G.99x
ADSL/SHDSL
Telco
G.993
VDSL
Telco
Analog
Analog
Digital
Digital
Fiber
Digital
33k
56k
64 ~ 128k
0.5 ~ 5M
5 ~ 20M
2
ITU Q4/15 Milestones
ITU-T
o 1997 – First Meetings
o 1998 – First Recommendation – G.hsdl
o 1999 – ADSL set of Recommendations
o 1999 – G.vdsl initiated
o 2001 – G.shdsl
o 2002 – ADSL2
o 2003 – ADSL2+
o 2004 – G.vdsl and line code decision
2004 June
3
ITU-T xDSL Standards 1999
ITU-T
G.ref
(G.995.1)
xDSL standard overview
G.hs
(G.994.1)
xDSL Initialization
and Negotiation
G.hdsl
G.dmt
(G.991.1)
G.test (G.996.1)
G.ploam
Test loops and
crosstalk models
Operations, Administration,
and Maintence protocol
G.lite
(G.992.1)
Main Body
North America
Main Body
2004 June
(G.992.2)
Splitterless ADSL
Full rate ADSL
HDSL
(G.997.1)
Annex A
Annex B
North America
ADSL above POTS
Europe
Japan
ADSL above ISDN ADSL above POTS
Annex C
Annex A
Annex B
Annex C
FDM
ADSL above POTS
Echo canceller
ADSL above POTS
Japan
ADSL above POTS
4
ITU-T
Splitterless ADSL (G.992.2 / G.lite)
o G.lite (G.992.2) similar to G.dmt (G.992.1)
o Two distinctions for consumer market:
• Splitterless operation
• Power management states
o Splitterless:
• No truck roll to install splitter at NID
• But need fast retrain and possibly microfilters
o Although “hot” in 1999, majority of
deployments now use full-rate ADSL
2004 June
5
ADSL (G.992.1 - a.k.a G.dmt)
ITU-T
o Asymmetrical Digital Subscriber Line
o Downstream (to the subscriber) rates ~0.5
to 5 Mbps
o Upstream rates of approximately 100 to
500 kbps.
o For a 1 Mbps downstream rate, the range is
~ 5 km (depends on cable gauge)
o ADSL modulation (line code) = discrete
multitone (DMT).
o 3 Variants (Annexes) for North America,
Europe, and Japan
2004 June
6
xDSL Handshake - G.994.1
ITU-T
o Common activation (handshake) procedure
for all xDSL modems.
• ADSL, VDSL, SHDSL, ANSI, ETSI, IEEE EFM
o Extremely robust modulation
• Works on all lines even with bridge taps
o Forward compatibility for all new xDSL
modem standards.
o Higher layers can indicate service and
application requirements
• Select most appropriate DSL.
• Flexibly tailor the service bandwidth and latency.
2004 June
7
xDSL Support Recommendations
ITU-T
o G.996.1 (G.test) - testing procedures for DSL
modems.
• Useful during manufacturer design and development.
• Not procedures for installing DSL modems.
o G.997.1 (G.ploam) - physical layer management
protocol for ADSL systems.
• Control data exchange on a sub-channel of the DSL
modems.
• Uses a SNMP MIB to easily integrate with existing
network management systems.
o G.995.1 (G.ref) - provides a reference and
overview of the DSL family of Recommendations.
2004 June
8
ITU-T xDSL Standards 2004
ITU-T
Rec
G.991.1
Anx Decription
A Two Pair
B CAP Modulation
G.991.2
A
B
C
D
E
F
G
H
Requirements - North America
Requirements - Europe
Requirements - Japan
Signal regenerator
TPS-TC Framing
North America Rates to 5.696M
Europe Extend Rates
Warm Start
Feb-2001
Feb-2001
G.992.1 Anx H
Feb-2001
Feb-2001
Dec-2003
Further Study
Dec-2003
G.992.1
A
B
C
D
E
F
G
H
I
ADSL over POTS
ADSL over ISDN
ADSL near TCM-ISDN
State Diagrams
Spiltters
Performance - North America
Performance - Europe (minimal)
Symmetric near TCM-ISDN
Short ADSL near TCM-ISDN
Jun-1999
Jun-1999
Jun-1999
Jun-1999
Jun-1999
Jun-1999
Jun-1999
Oct-2000
Mar-2003
A
B
C
D
E
Non-overlapped spectrum
Overlapped Spectrum
ADSL near TCM-ISDN
Performance - North America
Performance - Europe
Jul-1999
Jul-1999
Jul-1999
Jul-1999
Jul-1999
G.992.2
2004 June
Date
Oct-1998
Oct-1998
Rec
G.992.3
Anx Decription
Date
Jul-2002
A ADSL2 over POTS
Jul-2002
B ADSL2 over ISDN
Jul-2002
C ADSL2 near TCM-ISDN
Jul-2002
D State Diagrams
Jul-2002
E Spiltters
Jul-2002
F Performance - North America
G Performance - Europe (minimal) Jul-2002
Jul-2002
H Symmetric near TCM-ISDN
Jul-2002
I All digital ADSL near POTS
Jul-2002
J All digital ADSL near ISDN
K TPS-TC functional descriptions Jul-2002
Apr-2004
L READSL2 over POTS
M ADSL system with extended upstreApr-2004
G.992.4
A
B
C
D
E
F
G
H
I
ADSL2 over POTS
void
ADSL2 near TCM-ISDN
State Diagrams
No spiltters
Performance - North America
void
void
All digital ADSL near POTS
Jul-2002
N/A
Further study
G.992.3
N/A
Further study
N/A
N/A
Jul-2002
Rec
Anx Decription
G.992.5 A ADSL2+ over POTS
B ADSL2+ over ISDN
C ADSL2+ near TCM-ISDN
D State Diagrams
E Spiltters
F Performance - North America
G Performance - Europe (minimal)
H Symmetric near TCM-ISDN
I All digital ADSL near POTS
J All digital ADSL near ISDN
K TPS-TC functional descriptions
L READSL2 over POTS
Date
May-2003
May-2003
Further study
G.992.3
G.992.3
Further study
Further study
Further study
May-2003
Further study
G.992.3
Further study
G.993.1 A
B
C
D
E
F
G
H
I
Assymetric BandPlan
Symmetric BandPlan
Fx BandPlan
Requirements - North America
Requirements - Europe
Requirements - Japan
ATM-TC
PTM-TC
SCM
Nov-2001
Nov-2001
Nov-2001
Further study
Further study
Further study
Nov-2001
Nov-2001
Jun-2004
G.994.1
Handshake
Living
G.995.1
xDSL Overview
Living
G.996.1
Test Loops and Conditions
Living
G.997.1
Operations and Maintenance
Living
9
VDSL - G.993.1
ITU-T
o Very-high-speed Digital Subscriber Lines
o Asymmetric and symmetric data rates as
high as 5 to 20 Mbps.
o Typically combined with fiber to the
curb/building access.
o Spectrum up to 12 MHz, so the length of
the copper loops must be shorter than
ADSL.
o Must overcome many ingress / egress
issues.
2004 June
10
VDSL Problems to Solve
ITU-T
o Application
o Assymetric vs Symmetric, rates
o Spectrum / Band Plans
o Line code
2004 June
11
VDSL Typical Rate/Range tradeoff
ITU-T
VDSL
service type
Asymmetric
Short
Medium
Long
Symmetric
Short
Medium
Long
2004 June
Reach
[km]
Down
[Mbit/s]
Up
[Mbit/s]
0.3
1.0
1.5
50
25
13
6.4
3.2
1.6
0.3
1.0
1.5
25
13
6.5
25
13
6.5
12
VDSL spectral issue
ITU-T
o Different providers
may want spectrally
incompatible services
o Unbundling is strongly
influenced by spectral
compatibility
o At higher frequencies,
signals in adjacent
wire pairs are strongly
coupled.
D
U
0.138
3.
5.1
D
0.138
D
U
3.75
U
7.05
12.
D
5.2
U
8.5
12
o Maybe Dynamic
2004 June
Spectral Management
(DSM) is the future?
13
VDSL Line Code Selection
ITU-T
Single Carrier (QAM)
Multi Carrier (DMT)
n-QAM modulated
up
down
f
fB
f
∆f = fB/N
frequency spectrum
o DMT Selected as the Line Code for VDSL2
o Compromise: QAM as an Annex to DMT Main
Body in VDSL1
• January 2004; Publish July 2004
2004 June
14
G.shdsl - G.991.2
ITU-T
o Single pair high speed digital subscriber line
o Technology improvement of G.hdsl
(G.991.1) that will work on a single pair.
o Symmetric bit rates to 2Mbps (2001)
o New Extended bit rates to 6 Mbps (2003)
2004 June
15
Miscellaneous Q4/15 Projects
ITU-T
o G.voice
• Channelizing Voice on xDSL
o G.selt
• Single Ended Line Testing
o G.bond
• Bonding multiple pairs together
o G.nm
• Network Management
o G.pnt
• Phoneline Networking
2004 June
16
Q4/15 Ongoing Work
ITU-T
o VDSL2
• DMT only VDSL based on VDSL1 and ADSL2
o ADSL increments
2004 June
17
Calls to Action
ITU-T
o Regulators: Uniform regulations lead to
less variants worldwide
o Operators: Uniform requirements with
clear applications
o Standardizers: Reduce the options and
Annexes
2004 June
18
ITU-T
2004 June
19
xDSL Spectra
ITU-T
POTS
Upstream
Downstream
Mixed
ISDN
SHDSL
ADSL Annex A
ADSL Annex B
ADSL2 Annex M
ADSL2+ Annex A
VDSL
???
VDSL2
10K
100K
1M
10M
100M
Frequency Spectrum (Hz)
2004 June
20