xDSL
1
Network reference model
Access provider
Core
network
Service
provider
Transport
exchange
Access
network
TP
cable
fiber
WLL
Network provider
2
Customer
Premises
Network
Evolution of Access Network



3
Evolution based on Twisted Pairs(TP)
Evolution based on optical fiber
Evolution based on wireless network
국내 초고속 가입자 현황
xDSL
HFC
APT LAN 위성
합계
KT
4,625,841
498,306 5,632 5,129,782
하나로 통신
1,184,629 1,359,675 386,951
2,931,255
두루넷
1,284,963
8,543
1,293,506
온세통신
482,172
6,967
489,139
드림라인
73,075
87,554
3,663
164,192
데이콤
69,630
74,653
144,283
부가통신사업자
4,836
363,632
4,388
372,856
별정통신사업자 49,205
124,854
174,059
합계
5,937,586 3,647,626 1,108,328 5,632 10,699,172
점유율(%)
55.50
34.09
10.36
0.05
100
2003년 2월말
4
자료: 한국전산원
DSL 기술의 배경



5
One way to avoid enormous investment for
installing optical fiber local loop is to use the
traditional copper local loop.
The twisted local loop is actually capable of
handling bandwidths up to 1.1 MHz, but the
filter installed at the end of the line by the
telephone company limits the bandwidth to
4KHz. If the filter is removed, however, the
entire 1.1 MHz is available for data and voice
communications.
Thus, DSL technology provides higher data
rate in addition to support POTS at the same
time.
Various xDSL(1)

ISDN







6
2B+D
23B+D
HDSL(High data rate Digital Subscriber Line)
ADSL(Asymmetric Digital Subscriber Line)
SDSL(Symmetric Digital Subscriber Line)
VDSL(Very high data rate Digital Subscriber Line)
RADSL, MDSL, IDSL, UADSL
Various xDSL(2)



7
ADSL2
ADSL2+
VDSL2
Characteristics of major xDSL
T1/E1
Central
Office
(PSTN)
TP(2 pairs)
CO
Repeater
Line
Repeater
0.3~1km
HDSL
Central
Office
(PSTN)
HDSL
CO Unit
ADSL/
SDSL
Headend
(Video)
ADSL
CO Unit
End
User
(POTS)
Line
Repeater
1~1.8km
0.3~1km
HDSL
RT Unit
End
User
(POTS)
ADSL
RT Unit
End
User
(Video)
TP(2 pairs)
TP(1 pair)
PSTN
VDSL
Headend
(Video)
POTS
Optical
Network
Unit
PSTN
8
VDSL
CO Unit
TP(1 pair)
VDSL
RT Unit
End
User
(Video)
POTS
HDSL





9
T1/E1 rate with 2 TP pairs
Internet access, LAN service
 Mainly used for leased line service for
business customers
Covers 3.5km(12kf) using 196KHz bandwidth
without any repeater
 Less expensive than the standard T1/E1
leased line service
dual duplex: two transceiver
2B1Q Modulation
SDSL




10
T1/E1 rate with single pair
Data rate; 160kbps-2.048Mbps(symmetrical)
Distance: less than 3km
2B1Q
ADSL

Asymmetric bi-directional digital subscriber line



Data rate:1.5- 8 Mbps (downstream), 16-640 kbps
(upstream) depending on distance and line quality
Distance is up to 5.5km(18kft)
DMT(G.992.1, G.992.2)
Headend
ADSL
CO
Unit
TP 1pair
1.5 ~ 8 Mbps
16 ~ 640kbps
PSTN
11
ADSL
RT Unit
End
User
POTS
Frequency Bandwidth

Since data transmission is done on the
frequency between 30KHz and 1MHz, ADSL
provides data services as well as POTS at
the same time.
POTS
0.3
3.3
upstream
30
downstream
138
frequency (KHz)
12
1104
ADSL Modem and DSLAM
13
Line coding

Discrete Multitone(DMT)






14
ITU standard(G.992.1, G.992.2)
Combines QAM and FDM.
The whole bandwidth is divided into 256 channels.
For upstream data and control the channel 6 to 30
are used, each using 4KHz.
With QAM modulation, available bandwidth is
24x4000x15 = 1.44Mbps.
For down stream, channels 31 to 255 are used,
and we can achieve up to
224x4000x15=13.4Mbps
DMT
15
Bandwidth Division
16
ADSL2


Data rate: 8Mbps(down), 800kb/s(up)
Improve ADSL for stability rather than speed.




17
Improved initialization
On-line reconfiguration
Framing
DMT(G.992.3, G.992.4)
ADSL2+



Improve the downstream data rate of ADSL.
Bandwidth for downstream data transmission: 2MHz
downstream data rate






18
16Mb/s, 1.2km
10Mb/s, 1.8km
7Mb/s, 2.5km
Upstream, 1.5Mb/s
DMT(G.992.5)
However, there is little or no improvement of speed
for loops beyond 2.5km.
VDSL

Very high data rate digital subscriber line




VDSL line coding standards





19
Because of distance limitation, fiber cable should be installed up to the
curb, and from there twisted pair lines are used up to subscribers.
Depending on distances, up to 13-52Mbps(down), 1.5-2.3Mbps(up)
Bandwidth: 10MHz
ANSI: DMT
IEEE: DMT (EFM-Cu for short-reach)
ETSI: DMT/QAM
ITU-T G.993.1
Because VDSL is used for short distance, there are many technical
issued such as crosstalk to be solved.
xDSL Comparison
Data rate
types
up
20
down
distance
TP
POTS
IDSL
128kbps
~5.5km
1
X
SDSL
768kbps
~3.5km
1
X
MDSL
64~2,048kbps
~6km
1
X
HDSL
1.544Mbps(T1)
2.048Mbps(E1)
~3.5km
2
X
RADSL
128k~1Mbps 128k~8Mbps
~5.5km
1
O
UADSL
128~512kbps 128k~1.5Mbps
~6km
1
O
VDSL
640~2.3Mbps 13~52Mbps
~1.4km
1
O
New ADSL
50Mb/s
VDSL
VDSL2
10Mb/s
ADSL2+
ADSL
6Mb/s
1Mb/s
ADSL2+
0.5 1
2
4
3
거리
21
5
6
7 km
VDSL2



Adopts ADSL ‘s new features
Backward compatibility to ADSL family
Possible new features



22
Frequency beyond 12MHz
100Mb/s at 1km
Etc.
Migration Strategy
Wire Plant
Neighborhood
Curb
Premises
up to 8Mbps
Copper Loop
DLC
DSLAM
up to 8Mbps
DLC
FTTC
ONU
up to 52Mbps
155Mbps and beyond
FTTH
23
DSL Terminology
xDSL
=
x Digital Subscriber Line
ADSL
=
Asymmetric Digital Subscriber Line
RADSL =
Rate-Adaptive Digital Subscriber Line
UAWG
Universal ADSL Working Group (universal ADSL, ADSL Lite,
=
G.Lite, splitterless ADSL)
SDSL
=
Symmetric Digital Subscriber Line
HDSL
=
High Bit-Rate Digital Subscriber Line
HDSL2 =
High Bit-Rate Digital Subscriber Line, 2nd generation
SHDSL =
Single-pair High Bit-Rate Digital Subscriber Line
IDSL
=
ISDN Digital Subscriber Line
VDSL
=
Very High-Speed Digital Subscriber Line
DSLAM =
Digital Subscriber Line Access Multiplexer
xDSL = Physical layer technologies allowing transport of digital information over the
copper loop.
HFC(Hybrid fiber-coaxial)
25
HFC Overview




HFC networks use a hybrid of fiber optic and coaxial cable to make the
cable network bidirectional (two-way). The use of fiber-optic cable reduces
the need for amplifiers down to 8 or less.
Coaxial network has a tree & branch structure.
An area served by a SO is divided into several cells.
The size of a cell is decided by the number of subscribers.
splitter
Head end
Set top
box
ONU
Cable
modem
26
TV
PC
HFC 망
PP
Distribution center
(SO)
H/E
CMTS
Optical RTX
broadcast
Outdoor optical RTX
(ONU)
splitter
TBA
Tap-off
Coaxial cable
Power supply
CM
ISP
Cell 1
27
PP: program provider
Cell
SO: system operator
CM: cable modem
CMTS: cable model termination system
TBA: trunk bridge amplifier
N
Components

ONU(Optical Network Unit)


TBA


Split one RF signal into more than two RF signals.
Tap-off

28
Guarantee the loss of line signal of coaxial cables.
Splitter


Transforms between optical signals and RF signals in a cell.
It distributes equally RF signal into subscriber terminals.
Frequency bandwidth
upstream
5


29
42 54
Analog
broadcast
Internet
450
Digital broadcast
Value added services
552
750 MHz
The downstream data occupies 450-552MHz band. This band is
divided into 6MHz.
The upstream data occupies 5-42MHz band, which is also
divided into 6MHz channels.
 The 5-42MHz frequency band for upstream is very
susceptible to noises by consumer electronics devices and
signals caused by HAM, CB radios.
 For this reason, The low bit rate modulation technique such
as QPSK is used for stability.
Data rates
Data rates depending on modulation techniques
of DOCSIS modems
bandwidth
modulation
upstream
1.5MHz
QPSK
Data rate 2.5Mbps
30
Downstream
6MHz
16QAM
64QAM
256QAM
5Mbps
27Mbps
40Mbps
Characteristics



One cell serves up to 500-2500 subscribers.
Bidirectional transmission
Limitation of data rate


31
When 100 subscribers use at the same time, data
rate is reduced to less than 300kbps(downstream).
Because of tree & branch structure, the transmission
quality is deteriorated by signal interruption.
국내 HFC 망 연혁

1995년 종합유선방송(케이블TV) 사업 개시


PP(Program provider): 프로그램 공급자
SO(System operator): 지역 방송국
•
•
•

NO(Network operator):
•
•



1997년 KEPCO 양방향 시버 서비스 성공
1998년말 두루넷(KEPCO의 HFC망 사용) 사업 시작
1999년 하나로, 2000년 온세 통신 등 다수 사업자 참여
•
HFC망: KEPCO 1차 지역, 데이터 HFC망 구축
2000-2002년 초고속 가입자 사업 활성화




케이블 TV 분배망(PP-SO): 파워콤, KT(위성)
케이블 TV 전송망(SO-가입자): 파워콤, SO의 HFC 망
케이블 모뎀을 통한 인터넷 사업 시작


광역시, 대도시 1차 53개 지역
지역 중소 도시 2차 24개 지역
중계유선 3차
KT 시설분 SO 매각, 중계유선의 SO 전환
파워콤 분리
인터넷 가입자 증가로 데이터 HFC망 시설 폭증(하나로, 두루넷, SO 등 HFC 자가망
구축)
2003년 디지털 케이블 TV 도입 개시
자료: 파워콤㈜ KRNET2004발표자료
32
국내 인터넷 가입자 현황

전체 가입자 증가와 마찬가지로 현재 완만한 증가
추세로 인터넷 가입자의 포화 상태에 이르렀음을 알
수 있다.
2000.12
2001.2 2002.12 2003.12
2004.4
1,040만 1,118만
1,143만
전체가입자
398만
780만
HFC망가입자
139만
262만
355만
383만
402만
자료: 파워콤㈜ KRNET2004발표자료
33
Standards


CableLabs, DAVIC, IEEE 802.14, ATM Forum,
IETF의 IP over Cable Data Network
CableLabs(Cable Television Laboratories Inc.)




Non profit organization composed of cable modem
manufacturers.
CableLabs standards are adapted by ANSI, ITU-T
Also performs certificates.
DOCSIS(Data Over Cable Service Interface Spec.)
• DOCSIS 1.0(1999):
• DOCSIS 1.1:
• DOCSIS 2.0(2001):

34
Digital settop box standards: Opencable
• Cable Network Interface Standard(SCTE40/DVS313)
DOCSIS cable modem

DOCSIS 1.0(1999년)



DOCSIS 1.1(2001년)



Improve OoS functions
DOCSIS 1.0 can be upgraded to DOCSIS by software.
DOCSIS 2.0(2002년)



35
First commercialized standards
Bidirectional data transmission
Improve upstream data rate: 30Mbps
Symmetrical bidirectional service
H/W upgrade
HFC MAC

Credit-based MAC


For upstream transmission, the headend grants the
right to send data to cable modems.
CRA(Collision Resolution Algorithm)
• When cable modems send credit requests collision may
happen, When it happens, the headend detects the
collision, and notifies cable modems of it. Then the cable
modems backoff and retry after random intervals.
36
Future

Speed improvement


Downsizing of cells


37
Frequency bandwidth can be expanded upto
1.5Gbps, the speed can be increased upto
100Mb/s.
The current distance from ONU to subscribers
which is about 1km will be decreased to less than
500m.
Improve network monitoring system.
SDH (SONET)
38
Multiplexing of Telephone Lines
39
Multiplexing of Digital Signals
40
Digital Hierarchy
Table 6.1 DS and T lines rates
41
Service
Line
Rate
(Mbps)
Voice Channels
DS-1
T-1
1.544
24
DS-2
T-2
6.312
96
DS-3
T-3
44.736
672
DS-4
T-4
274.176
4032
Digital Hierarchy (Europe)
Table 6.2 E line rates
42
E Line
Rate
(Mbps)
Voice
Channels
E-1
2.048
30
E-2
8.448
120
E-3
34.368
480
E-4
139.264
1920
Synchronous Digital
Hierarchy(SDH)
PDH
DS-0
DS-1
DS-2
DS-3
DS-4
43
0.064
1
T-1 1.544
24
T-2 6.312
96
T-3 44.736 672
T-4 274.176 4032
SDH
STM-1
STM-4
STM-16
STM-48
OC-3
155.52
OC-12 622.08
OC-48 2488.32
OC-192 9953.28
Synchronous Digital
Hierarchy(SONET)
44
STS
OC
Rate (Mbps)
SPE (Mbps)
User (Mbps)
STS-1
OC-1
51.84
50.12
49.536
STS-3
OC-3
155.52
150.336
148.608
STS-9
OC-9
466.56
451.008
445.824
STS-12
OC-12
622.08
601.344
594.432
STS-18
OC-18
933.12
902.016
891.648
STS-24
OC-24
1244.16
1202.688
1188.864
STS-36
OC-36
1866.23
1804.032
1783.296
STS-48
OC-48
2488.32
2405.376
2377.728
STS-192
OC-192
9953.28
9621.604
9510.912
SONET transport network
45
TDM-based transport network
Home
POP(주노드국)
CO(수용국)
ADSL (1.5M~8Mbps)
DSLAM
GES
B-RAS
MTU
수용국
LAN A
DS3/
OC3
T1
LAN B
STU
LAN C
T1 (1.544Mbps)
FLC
FLC
T1
GSR 2.5Gbps
(POS)
Internet
Edge
Router
DS3/
(7500)
OC3
OC3/
OC12
ADM
ADM
STM-4 (2.5G)
T1 1.544 Mbps
동선
T1 1.544 Mbps
CSU
OC3
DSC
(D/MUX)
SONET/SDH
ADM
DSC
(D/MUX)
ADM
수용국
LAN D
CSU
TDM multiplexing/Circuit switching
64Kbps
No Statistical multiplexing
1.544Mbps
1
46
STS-N
OC-N STS-N
STS-1
1
…
STS-1
STS-1
…
28
…
T1 1.544 Mbps
…
24
STS-1
(45M)
…
…
64Kbps
1.544Mbps
1
1
24
28
T1 1.544 Mbps
SONET frame
47