1. Broadband Access Networks and Services
EE Spring 2004
Broadband Access Networks and Services
Chapter 2
Twisted-Pair based Access Networks
Byeong Gi Lee
Seoul National University

2. 2. TP-based Access Network
Limitation of POTS and ISDN
Digital Loop Carrier
DSL Technologies – IDSL, HDSL, SDSL, ADSL, G.Lite, VDSL, and Comparisons
ADSL Access Network, Architecture, Components, and Protocol Model
Spectrum Allocations
Modulation Techniques
Applications, Challenges, and Penetration
BGL

3. Structure of Access Network
ADSL : Asymmetric Digital Subscriber Line
DBS : Direct Broadcast Satellite
FTTC : Fiber To The Curb
HFC : Hybrid Fiber Coaxial
LMDS : Local Multipoint Distribution System
MMDS : Multi-channel Multipoint Distribution System
MSO : Multiple Service Operator
TP-based AN
Digital DBS
Fiber or
Wireless
MMDS/LMDS
LMDS only
Hub Station
DBS STB/
MMDS/LMDS STB
64Kbps
ISDN Adaptor
ISDN Line
MSO
/CO
Analog Modem
56Kbps
앞 절에서 소개한 기술을 개략적으로 도시한 그림입니다.
6Mbps
ADSL Modem
Home
Terminal
Coax
30Mbps
640Kbps
Cable Modem
Fiber
HFC
3Mbps
ONU
Coax or Copper
Fiber
VDSL Modem
52Mbps
FTTC/FTTO
3Mbps
BGL

4. Access and Backbone Infrastructure
BGL

5. Limitation of POTS and ISDN
Limitation in existing subscriber lines
Restrictive for high-speed service
Limited data-carrying capacity of 56kbps using V.90
Analog mode and suppressing filters above 3,400Hz
Limitation of POTS
Customer connected over thin-wire pairs (26guage, 0.5mm)
Local loops are bundled in binder groups (feeder part)
Limitation of ISDN services
Not possible to provision ISDN and POTS in same local loop
Internet Problems for POTS and ISDN
Both carries data in circuit mode (voice switch)
BGL

6. Digital Loop Carrier
T1 or HDSL base feeder (connecting CO and RT)
BGL

7. xDSL
Advanced modulation technology based bandwidth expansion (128kbps to 52Mbps)
xDSL easier to install than ISDN
needs inside wiring work and copper line cleaning
Variations depending on symmetry of upward/downward data rates (ADSL vs SDSL) and the location of equipment (ADSL vs VDSL)
Supports POTS using splitter (split flter). But G.Lite can eliminate splitter.
HDSL can replace T1/E1 without repeaters.
BGL

8. Configuration of xDSL T1/E1 HDSL ADSL VDSL Central Office (PSTN) BGL
End
User
(POTS)
Central
Office
(PSTN)
TP (2 pairs) CO
Repeater
Line
Repeater
Line
Repeater
T1/E1
0.3~1km
1~1.8 km
0.3~1km
End
User
(POTS)
Central
Office
(PSTN)
TP (2 pairs)
HDSL
HDSL
CO Unit
HDSL
RT Unit
End
User
(Video)
Headend
(Video)
ADSL
CO Unit
ADSL
TP (1 pair)
ADSL
RT Unit
xDSL(Digital Subscriber Line, x=family member; A, H, S, U, V)는 기존의 트위스트 페어 전화선을 사용하는 디지털 가입자 선로(Digital Subscriber Line) 기술 집합을 의미한다. xDSL 기술은 비대칭형 전송방식인 asymmetric DSL(ADSL), 대칭형 전송 방식인 high-data-rate DSL(HDSL) 및 single-line DSL(SDSL), 단거리에서 초고속 데이터 전송방식인 very-high-rate DSL(VDSL), 및 전송선로 특성에 따라 전송속도가 가변이 되는 rate-adaptive DSL(RADSL) 등으로 구별된다.
PSTN
POTS
End
User
(Video)
Headend
(Video)
Optical
Network
Unit
VDSL
VDSL
CO Unit
TP (1 pair)
VDSL
RT Unit
PSTN
SPF
POTS
BGL

9. IDSL
ISDN Digital Subscriber Line is a cross point between ISDN and xDSL
Made available with the introduction of ISDN
2B + D basic rate access (BRA), 144kbps+16kbps
B: 64kbps for voice or data
D: 16kbps for call control or packet data
Transmission rate of 80 ksps
2B1Q modulated
Travels over 5.4 km over 24 gauge (.5mm)
BGL

10. HDSL Comparable with T1/E1 lines
Mbps rate transmission with 2 pairs
Can replace T1/E1 lines without repeaters
For T1 rate (1.5Mbps), two TP wires are necessary
For E1 rate (2Mbps), three TP wires are necessary
2B1Q Modulated, CAP, DMT
2B1Q: 3.6km, CAP:5.5km over 24 gauge
Interference problem when bundled in large size
BGL

11. SDSL Symmetric (or Single-line) HDSL (SHDSL, SDSL)
Two-wire (single pair) implementation of 2B1Q or CAP
Data rate of 384kbps~2Mbps (Sub-T1/E1 rates obtainable)
HDSL2 (G.SHDSL) stadard
Symmetric 2.3 Mbps over a single loop pair
Symmetric 4.6 Mbps over two loop pair
Echo cancellation and adaptive equalization
BGL

12. ADSL Up/down asymmetric bandwidth
For use in Internet, VOD like applications
One pair - good for residential use
1.5/2 ~6/8 Mbps down, 16~820 kbps up
Up to 5.4km without repeaters (0.5mm)
DMT (standardized), CAP (market) modulation
POTS split through split filter (SF)
Rate-Adaptive DSL (RADSL) - line condition
Universal ADSL (UADSL) - without split filter
BGL

13. ADSL G.Lite
ITU G.992.2
Easy and consumer-installable due to no need of POTS splitters like in full-rate ADSL (UADSL)
Offers the services of ADSL at a lower speed
POTS service possible by reducing the transmission power when off-hook
Fast retrain procedure: 1~2 s cessation of service
Longer reach and much less power than full-rate ADSL
BGL

14. VDSL Very high data rate, (a)symmetric DSL
Drop line for FTTC application
13~52 (~155) Mbps down depending on distance
300 m to 1.5 km distance (from curb to home)
CAP, DMT,QAM (DAVIC) modulation
POTS split through split filter (SF)
Standardization (DAVIC, ANSI T1E1.4, ETSI TM6, FSAN)
BGL

15. ADSL vs. G.Lite Full-Rate ADSL G.Lite ITU Specification ITU G.992.1
ANSI T1.413
ITU G.992.2
No ANSI specification
Also known as
G.dmt
Splitterless ADSL
POTS
Yes, using a single splitter
in home
Yes, using microfilters at each
analog handset
Modulation scheme
DMT
Phones
only after splitter
freely connected anywhere
Subbands
256
128
Downstream speed
6 Mbps, maybe more for
shorter distances
Up to T1
Upstream speed
Up to 512 Kbps
Professional installation
Hopefully no
Yes, for splitter and inside
wiring
BGL

16. ADSL vs. VDSL POTS/ISDN, therefore requiring splitters Full-Rate ADSL
Modulation techniques
Yes
DMT, using 256 bands with
4 kHz spacing
VDSL
DMT, CAP, or QAM
DMT modulation would use
256
band with 40 kHz spacing, or
2048 bands with 4 kHz spacing
Dual latency
Spectrum Allocation
Up to 1 MHz
Up to 30 MHz
Downstream bit rate
2 to 3 Mbps
Various up to Mbps
Upstream bit rate
Various up to T1
Various up to 6 Mbps
Standardization
ASNI T1.E1
ADSL Forum
ITU G.992.1
ITU SG 15, G.vdsl, G.993
Distance to ONU
Up to 5000 meters
300 to 1000 meters
BGL

17. Comparison of xDSL (1) Modulation Scheme ISDN 2B1Q 64 Kbps, 128 Kbps
ANSI T1.601
Uses 4B3Q coding in
some
European countries
IDSL
HDSL
HDSL-2
SDSL(ETSI)
Up to 2 Mbps
2 Mbps
Downstream
Bit Rate
Upstream
POTS
Support
Comments
Uses ISDN TA
Uses four wires; current T1
service
PAM-16
Uses two wires; not rate-
adaptable
Yes
Uses two wires; rate
BGL

18. Comparison of xDSL (2) G.Lite ADSL Mutiple Virual Line (MVL)
One Megabit
Modem
VDSL
2 Mbps
1.5 Mbps to
6Mbps
DMT
512 Kbps
Yes
ITU G.992.2
CAP
64 Kbps to
800 Kbps
Mostly Paradyne
ANSI T1.413
768 Kbps
Paradyne
QAM
1 Mbps
320 Kbps
Proprietary to Northern
Telecom; residers in Nortel
loop carrier system
QAM/CAP
12.96 Mbps to 51.84
Mbps
3 Mbps
Range of 300 meters for top
speeds; ANSI T1.E1.4, ETSI
and ITU Study Group 15
BGL

19. Comparison of xDSL (3)
* Distance for 0.5 mm (24 gauge) TP wires
BGL

20. ADSL-based Access Network
Switch
0~4 kHz
Splitter
Splitter
PSTN
Subscriber line
DSLAM
Data
Comm.
Network
ATU-C
ATU-R
T1.413 Issue 2 : Down 25 ~ 1104 kHz,
Up ~ 138 kHz
UADSL : Down 138 ~ 552 kHz,
Up ~ 138 kHz
Subscriber line
UADSL-R
* DSLAM : Digital Subscriber Lines Access Multiplexer
* ATU-C : ADSL Transceiver Unit, Central
* ATU-R : ADSL Transceiver Unit, Remote
* Splitter-less in UADSL
BGL

21. Generic ADSL Access Network Architecture
BGL

22. ADSL Components ADSL Transceiver Units POTS splitter
Physical layer device for frequency allocation, echo cancellation, FDM, rate adaptation, etc.
POTS splitter
Lowpass/highpass filter that separates analog voice from ADSL frequencies
DSL Access Multiplexer
Houses a set of ATU-C interfaces, mux/demuxes traffic from multiple ATU-Cs onto a single high-speed trunk
BGL

23. Protocol Model for Data Services over ADSL
BGL

24. Typical Protocol Stack for Access Network
BGL

25. Bandwidth Requirement
Application
File Type
File Size
Modem
28.8 kb/s
ISDN
128 kb/s
xDSL
384 kb/s
1.5 Mb/s
6.1 Mb/s
All User 30 kB
8.3 sec
1.9 sec
0.63 sec
0.16 sec
0.04 sec
Consumer
Digitized Photo
125
34.7 sec
7.8 sec
2.6 sec
0.6 sec
0.2 sec
Business User
Word Files
250 kB
69.4 sec
15.6 sec
5.2 sec
1.3 sec
0.3 sec
Telecommuter
Videoconferencing
384kb/s No
YES
Telemedicine
X-ray
5 MB
23.1 min
5.2 min
1.7 min
25.9 sec
6.5 sec
Remote LAN Ac c
ess Bulk File
20 MB
1.5 hr
20.0 min
6.9 min
26.0 sec
* Acceptable response time < 3.0 sec
BGL

26. Concept of Spectrum Allocation
(Numbers for example)
ISDN
ADSL (Down)
Power
Spectra
POTS
ADSL
(Up)
ADSL(Asymmetric Digital Subscriber Line)은 “비대칭형디지틀가입자회선”으로 해석되는데 엄밀한 의미에서 회선자체를 말하는 것이 아니라 정확히 말하면 전화회선의 미사용 대역폭을 이용하여 데이터속도를 혁신적으로 증가 시키는 전화선 양단의 모뎀을 지칭한다. ADSL은 1989년 Bellcore에서 전화선으로 동영상 즉 VOD서비스를 제공하겠다는 그 당시는 가히 혁명적인 개념에서 태동된 기술이다. 그러나 Contents의 빈약, 수요기반의 미성숙, VOD기술의 불완전으로 인하여 세인의 관심사에서 멀어져 사장된 기술로 인식되어 오다가 지난 95년부터 인터넷 붐이 일어나면서 다시 빛을 발하기 시작했다. ADSL의 가장 큰 특징은 전화국과 가입자간의 데이터 전달속도가 비대칭이며, 상향측 속도는 640kbps속도를 가지나, 하향 전달속도는 최고 9Mbps속도까지 제공 가능하다는 것이다.
하향전달속도는 전화국에서 가입자까지의 전화선의 거리, 직경, 브리지 탭의 유무, Interference의 세기 등 다양한 요소에 의하여 영향을 받으며, 특히 신호감쇄는 라인의 길이가 증가하고 주파수가 높을수록 급격히 증가한다. ADSL모뎀은 전화선의 직경이 0.5mm(24AWG)인 경우 각 1.5Mbps하향신호는 5.5km까지 전달할 수 있다. 한국통신의 가입자 평균거리가 2.5km이고 95%가 5.5km이내임을 감안한다면 ADSL 도입을 위한 선로상태는 유리한 편이며, 특히 브리지 탭이 없는 것은 ADSL기술을 채용하는 데 있어 큰 장점으로 작용할 것이다. 4 10 80
100
200
1000 kHs
BGL

27. Spectrum Allocations for xDSL
FTT Exchange, FTT Cabinet
BGL

28. ADSL Operation (1) Two services of ADSL: Voice Service (1)
transparent access to legacy voice service
high-speed digital service
Voice Service (1)
Provision of voice service relatively simple
In-home configuration
Frequencies below 3400Hz shunt by POTS splitters to POTS wiring at home and to voice switch at CO
NID (or NT) by telco powering, ATU-R by local powering
Voice service not to be subject to home wiring impairments
Protection of NID from lightening required not to damage home electronics.
So professional assistance needed for splitter installation
BGL

29. ADSL Operation (2) Voice Service (2)
Three possible locations of POTS splitter:
LPF at NID and HPF at ATU-R;
both filters in ATU-R;
both filters in NID
Three constraints:
local powering ATU-R;
voice not to be subject to impairments of home wiring
LPF relatively large, so does not fit into NID
These three constraints suggest POTS splitter and ATU-R should be separated
BGL

30. ADSL Operation (3)
One proposal from British Telecom
BGL

31. ADSL Operation (4) Digital Service (1) 1. Determine latency:
Video traffic subject to burst error, so interleaving and FEC used.
ANSI provided 500microsecond burst protection against impulse noise, creating 20ms latency.
But data service has no such requirement as higher-layer protocols can perform error correction, - delay of only 4ms.
So ADSL provides two logical data channels – fast (4ms) and slow (20ms)
Video on slow channel due to FEC and interleaving
Data on fast channel only with (de)modulation delay
ATU-R determines which latency type to take at start-up
BGL

32. ADSL Operation (5) Digital Service (2) 2. Determine bit rate:
RADSL adapts to the line condition via a negotiation process
When powered on, ATU-R probes the line to determine signal carrying capacity.
Signal-carrying capacity is a function of distance, noise, and allowable margins
Negotiation goes between ATU-C and ATU-R for maximum sustainable bit rate (out of four start-up rates, ANSI)
Entire negotiation within 20s.
BGL

33. ADSL Operation (6) Digital Service (3) 3. Perform auto-configuration:
Configuring IP addresses and software filters for ATU-R
Relatively straightforward since each user has a dedicated ATU-C
Manually configured by DSLAM or some form of software tunnel between ATU-R and a device
Method differs depending whether ATU-R or the end system is IP-aware
If ATU-R and PC is IP-aware DHCP client is one autoconfiguration technique
BGL

34. ADSL Operation (7) Digital Service (4) 4. Digital Data Transfer
After startup complete, data transferring
ATU-R accepts data from home networking over an Ethernet, ATM25, or other digital protocols, encapsulates, and then sends out.
MAC protocol is not required unlike HFC
Dynamic rate adaptation: ATU-R and ATU-C renegotiation during data transmission by periodic testing of line conditioning -- retraining time will be required in support of this.
BGL

35. Modulation Techniques
2B1Q (2 binary, 1 quaternary)
DMT (discrete multi-tone modulation)
CAP (carrier-less amplitude and phase modulation)
QAM (quadrature amplitude modulation)
QPSK
BGL

36. 2B1Q -3 -1 +1 +3
Bits
Quads
BGL

37. DMT (1) DMT: Sub-channel based data rate allocation BGL TWISTED-PAIR
Bits/chan
Bits/chan
Atten
Frequency
Frequency
Frequency
TWISTED-PAIR with TAP, AM/RF, and XTALK
Bits/chan
Atten AM
Bits/chan
TAP
xtalk
Frequency
Frequency
Frequency
BGL

38. DMT (2) DMT Transceiver Block Diagram S BGL T’=TDMT/2N Transmitted
signal
Encoder
and
buffer
b=RT
2N Point
IDFT
Parallel to
serial
converter
DAC
LPF
R b/s
N QAM
Symbols
2N Times Domain
Samples
T’=TDMT/2N
Decoder
DFT
Serial to
Parallel T’
Channel S
Noise
Received
N개의 부채널을 가진 기본적인 DMT송,수신 system은 위 그림과 같다. 입력 bit stream(R bps)은 b bits(b=RT)의 블럭 단위로 쪼개어져 저장된다. T(secs)는 symbol period를 1/T(frequency)는 symbol rate를 나타낸다.
한 블럭에 할당된 b bits는 N~개의 부채널에 각각 bi(i=1,2....N) bits씩 각부채널의 SNR 특성에 따라 분배된다.
그 다음 각각의 부채널의 bi bits는 QAM constellation상의 한 점인complex subsym -bol X(=│Xi│?Xi)로 encode 된다.
예를 들어 i번째 부채널에 bi = 4bits씩이 할당되게 되면, 현재의 b bits 블럭의 입력 비트열중 i 번째 부채널에 할당된 4bits에 해당하는 데이터(e.g: 1011)를 16-QAM의 1011에 해당 하는 subsymbol로 encode 하게 된다.
일단 N개의 부채널에 b bits가 bi bits씩 할당되고 QAM symbol Xi로 encoding되고 N개의 symbol을 IFFT를 사용하여 변조하게 된다.전송채널을 통해 실제로 전송되는 신호는 time domain에서 real 신호여야 하기때문에 , 할당된 N~개의 complex subsymbol Xi의 conjugate symmetric 신호를 N + 1부터 2N까지 배열하여 N-point IFFT를 함으로써 N개의 real-valued time domain samples, n(n=0,1, N-1)을 얻는다.
DMT modulator의 sampling rate 1/T'는 NT'=T로부터 1/T'=N/T, 즉symbol rate의 N배가 됨을 알 수 있다.
BGL

39. DMT (3) Features Issues frequency efficiency
symbol length per sub-channel longer
frequency selective noise avoided
Issues
complexity, power consumption
timing and synchronization critical
ANSI standard
BGL

40. CAP (1) CAP Transceiver Block Diagram + Encoder Inphase filter
Quadrature +
DAC
LPF
Input
signal
Decoder
Output
ADC
Decision
device
CAP방식은 single carrier 방식으로서 송신부에서 2개의 baseband 신호를 in-phase와 quadrature filter를 이용하여 passband spectral shaping하여 전송하는 방식이다.
QAM과 CAP의 신호는 같은 구조 이나 단지 차이점은 QAM의 경우에는 쉐이핑 필터의 입력에 ejwcnT가 곱해진 신호를 사용하는 반면CAP에는 ejwcnT가 곱해지지 않은 raw심볼을 사용한다.
BGL

41. CAP (2) 16CAP BGL ... b2 b3 b0 b1 b2 b3 b0 b1 b2 b3 b0 b1... t
quadrant
point within quadrant
symbol Qn 11 01 +3 10 11
b2 b3 01 00
current state 10 00 +1 00 01 -3 -1 +1 +3 In 01 00 00 10 11 -1 10 11 10 -3 01 11
BGL

42. QAM 16QAM : Downstream in DAVIC VDSL In-Phase I n Filter + Data Band
Symbol
Pass
Signal
Input
Encoder _
Filter
Output Q n
Quadrature
Filter Q n 11 01 +3 10 11
b2 b3
increasing time 01 00
current
lsb
msb
TC layer
state
byte alignment 10 00 +1 00 01 b2 b3 b0 b1 b2 b3 b0 b1 b2 b3 b0 b1 b2 -3 -1 +1 +3 I n
quadrant 01 00 -1 00 10
point within quadrant 11 10
symbol n (0..3)
symbol n+1 (0..3) 11 10 -3 01 11
BGL

43. QPSK QPSK: Upstream DAVIC VDSL Transmit I n Filter + cos Data Band
Symbol
Pass
Signal
Oscillator
Input
Encoder _
Filter
Output
sin Q n
Transmit
Filter +1 -1 00 01 11 10
b0 b1 I n Q b1 b0
increasing time
lsb
msb
byte alignment
TC layer
symbol n
n+1
n+2
n+3
BGL

44. CAP vs. DMT CAP DMT Power consumption Lower, fewer gates
Higher peak/average, but will
likely narrow gap
Forward carriers 1
256
Return carriers 32
Increment
320 Kb
32 Kb
Adaptive equalizers
Needed
None
Licensing
Globespan
Many sources
Standardization
In process
ITU and ANSI
BGL

45. xDSL Applications (1) High-speed Internet Access Telecommuting
residential and business area
Intranet access to link
Remote Office and Branch Office (ROBO)
low cost, high throughput LAN-to-LAN connectivity
Telecommuting
Small Office / Home Office (SOHO)
BGL

46. xDSL Applications (2) On-demand type applications
VOD, home shopping, tele-education, Interactive TV
Frame relay / ATM network access
Leased line provisioning (HDSL/SDSL)
replacing conventional T1/E1 leased line
FTTC using VDSL
BGL

47. Technical Challenges of xDSL (1)
End-to-end loop qualification impacted by
Loop length, loading coils, quality of E2E splicing of wiring segments, multiple changes of wire gauge, home wiring, age, corrosion, hostile binder groups, crosstalk, and bridged taps…
Crosstalk
Near-end crosstalk (NEXT)
Far-end crosstalk (FEXT)
Bridged Taps
Y form branch => source of echo
BGL

48. Technical Challenges of xDSL (2)
Powering remote terminals
Local power used to power DSL equipment; battery backup
Spectral masking
Long-term narrowband interference such as, AM radio and amateur radio ingress
Notching out specific frequencies
Impulse noise
Short-term interference with duration of 100ms with peak power of 10mv
ART-R maintenance
Software upgrading such as, algorithms
BGL

49. xDSL Penetration Worldwide (1)
Sources from Point-Topic
77 million broadband lines worldwide at June 2003
60% of all broadband lines are xDSL (46.7 million)
DSL lines grew by 30% in the first half of 2003, cable modems by 16.4%
Fast increase in Japan and China
Growth appears to be slowing in Korea and USA
Expected 60 million xDSL subscribers by end of 2003
BGL

50. xDSL Penetration Worldwide (2)
BGL

51. xDSL Penetration Worldwide (3)
BGL

52. xDSL Penetration Worldwide (4)
BGL

53. xDSL Penetration Worldwide (5)
USA
BGL

54. xDSL Penetration Worldwide (6)
China (1)
BGL

55. xDSL Penetration Worldwide (7)
China (2)
BGL

56. xDSL Penetration Worldwide (8)
Japan (1)
BGL

57. xDSL Penetration in Korea (1)
11 million broadband access subscribers (Jun. 2003)
6.2 million xDSL (56.5%), 3.8 million Cable (34.5%)
Source: 정보통신부
*아파트LAN: LAN based Broadband Internet Service
BGL

58. xDSL Penetration in Korea (2)
Subscribers for Service Providers
BGL
Source: 정보통신부

59. xDSL Penetration in Korea (3)
Service Providers and Base Technologies
BGL
Source: 정보통신부

60. Access Network Architecture (2)
Typical technology-independent protocol stack
A typical protocol stack for an access network.
ATM
applications
Application/services
SNMP, TFTP, DHCP, security management, etc
TCP/UDP
IP, ICMP
PPP
ARP
LLC
Link security
AAL5 and ATM
MAC TC
Transmission convergence (TC)
Physical
BGL

61. Service Architecture over ADSL (1)
Basically a p2p switched transmission technology
IP over PPP over HDLC over ADSL or
IP over ATM over ADSL
ADSL intended to be used as access technology for Internet or LAN access in conjunction with analog telephony service
Various architectural models possible to meet the specific service offerings, interconnection to the backbone networks, and strategic direction of a network provider
BGL

62. Service Architecture over ADSL (2)
A plausible communications model for data over ADSL
An example communications protocol model for data services over ADSL.
Note that this model is fairly generic to work on any physical medium IP
Any data
link layer or
ATM
with TC *
PPP
HDLC
AAL5
MAC
PMD TC
802.2 LLC
803.3 MAC
802.3
10BaseX
Switch #
and/or
router
Internet/
WAN
ADSL-C modem
ADSL-R modem
Home terminal
Copper wire
Optionally, a standards-based ATM
UNI interface can be provided to
connect directly to an ATM backbone
Switch can be a LAN, a frame relay
switch, or an ATM switch
BGL

63. Service Architecture over ADSL (3)
ATU-C: encoding and modulating the DS data and combining the analog POTS signal; in US, demodulating the signal received from the customer and outputting a data stream and POTS signal
Three main architecture options
Bit-synchronous mode
ATM cell mode
Packet mode
Type of mode is independent of underlying line encoding method used
BGL

64. Service Architecture over ADSL (4)
Generic reference architecture at logical model
A generic ADSL access network architecture.
Access
node *
Service-specific
interfaces
Access node can be co-located with the CO
switch, or be remoted in the distribution plant.
Internet
backbone
ATM
network
Private
leased-line
Other
networks
(e.g., FR)
ATU-C
ATU-R
Premises
LAN
cable
wiring PC
Set-top
PSTN
Passive
split
To phones
Network
interface
Copper loop
BGL

65. Service Architecture over ADSL (5)
Bit-Synchronous Mode
Traditional circuit-switched network digital hierarchy
Interface with either a backbone voice or data network via existing CBR circuit-switched services
Plesiochronous digital hierarchy supported in ADSL
DS1 (1.544 Mbps); E1 (2.048 Mbps); DS2 (6.312 Mbps); E2 (8.448 Mbps)
An application will typically use the appropriate bandwidth from the digital hierarchy meeting the bandwidth demand
Data applications such as Internet and LAN interconnect supported in this mode
BGL

66. Service Architecture over ADSL (6)
Packet-based Transport over ADSL
MUX in the access node adapts the protocol carried over ADSL to one of the commonly used packet transport services
Switching and/or routing of variable-length layer 2 frames and/or layer 3 packets over an ADSL link
PPP and FR are the most popular L2 protocols (HDLC-like) supporting any of L3 protocols (IP, IPS,..)
PPP encapsulation: allows many different protocols to be transported over p2p links
FUNI encapsulation: variable-size frame to be transmitted is encapsulated in FUNI frame
BGL

67. Service Architecture over ADSL (7)
ATM-based Transport over ADSL
ATU-R provides a native ATM interface to the user device or a legacy LAN interface with segmentation and reassembly (SAR) functionality
Edge switch
ATM multiplexer in access node
Concentration and ATM layer routing function
Alternatively, SAR and network layer routing can be provided in CO such as DSLAM
On access side: multiplicity of service protocols (TCP/IP, PPP, FR, ATM cell relay, ATM circuit emulation) over a variety of physical layer protocols (HDSL, ADSL, DS1)
On backbone side: standard ATM user-network interface for transport to ATM switch, which can connect to ATM backbone
BGL