This presentation was presented in the ITU/BDT Arab Regional Workshop on "DSL Services and Applications", held in Cairo (EGYPT) during the period 4-6 March 2003. It addresses the following main topics: What is DSL? Why use DSL? How DSL works? Evolution of DSL Technology DSL System Components DSL System Applications

1. ITU/BDT Arab Regional Workshop on :
“DSL Services and Applications”
4 – 6 March 2003, Cairo/EGYPT
DSL :
Concepts, Technologies, and Prospects
By
Dr. Mahmoud T. El-Hadidi
Professor of Computer Networks
Dept. of Electronics & Electrical Communications
Faculty of Engineering – Cairo University

2. Outline
‰ What is DSL ?
‰ Why use DSL ?
‰ How DSL works ?
‰ Evolution of DSL Technology
‰ DSL System Components
‰ DSL System Applications
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

3. What is DSL ?
• DSL = Digital Subscriber Line
• DSL is a transmission technology
based on copper loop
that achieves broadband speeds ( 8 Mbps + )
• DSL sends digital signals over subscriber
loop, including :
data
digital video
digital audio
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

4. What is DSL ?
C O
C O
C O
C O
C O
DLC
RT
Corporate
Network
Internet
Service
Provider
Interactive
Video
Network
iMac
iMac
iMac
iMac
iMac
TI/E1/Fiber
DACS or other network
transmission equipment
MDF
Telephone
switch
Transport
system
Analog or ISDN modem data
To
Inter-CO
network
To homes or
offices
High speed
data
DLC
system
To C O
Copper wire
Copper wire
Copper wire
Copper wire
Copper wire
Home
or
office
Home
or
office
Home
or
office
Home
or
office
Home
or
office
Netrwork Service Provider Netrwork Access Provider
Service Users
Service Users
Inter - C O Network
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

5. What is DSL ?
• DSL sends digital signals, either :
without modulation (baseband transmission)
or with modulation (carrier transmission)
• DSL systems fall into two main categories :
Symmetric DSL
Uplink speed (to CO) = Downlink speed (from CO)
Asymmetric DSL
Uplink speed (to CO) < Downlink speed (from CO)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

6. Why use DSL ?
• Network Service Providers (NSP) are offering
applications with higher BW. E.g. :
Web downloads - Video distribution
Æ Backbone NW should be enhanced
OK (via optical fibers, ATM switches, … )
Æ Access NW for NSP should be enhanced
OK (via T1/E1, T3/E3,… )
Æ Access NW for Service Users should be
enhanced
?
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

7. Why use DSL ?
• Traditionally, use is made of :
Analog modems Æ 56/64 kbps
reasonable cost - reach =6 km
ISDN Æ 128 kbps/1.544 or 2.048 Mbps
costly - reach = 3 km
T1/E1 Æ 1.544/2.048 Mbps
very costly – reach = 1 km
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

8. Why use DSL ?
C O
C O
C O C O
Corporate
Network
Internet
Service
Provider
Interactive
Video
Network
iMac
iMac
iMac
DACS or other network
transmission equipment
MDF
Telephone
switch
Transport
system
Analog or ISDN modem data
To
Inter-CO
network
To homes or
offices
High speed
data
Home
or
office
Home
or
office
Home
or
office
Netrwork Service Provider Access Network Service Users
Inter - C O Network
56 kbps
analog
modem
BRI/PRI
NTU
TI/E1
CSU/DSU
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

9. Why use DSL ?
• Alternatively, can use :
Fiber (FTTH, FTTN, FTTC, HFC)
Æ10’s of Mbps
extremely costly – long time to market
reach =10’s of kms
DSL Æ Up to 2.3 Mbps (symmetric)
Up to 9 Mbps (asymmetric)
reasonable cost - reach = 6 km
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

10. Why use DSL ?
• DSL can :
- Transform nearly 700 million phone lines –
installed worldwide – instantly, into multimegabit
data pipes
- Offer a win-win scenario for service providers
and service users
- Enable service providers to provide
differentiated services to different users, in a
managed way
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

11. Why use DSL ?
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

12. How DSL works ?
• Main philosophy :
Pump more bits in same copper wire
• Strategy 1:
Break traditional voice BW barrier, by
removing loading coils
removing bridged taps
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

13. How DSL works ?
• Strategy 2:
Combat effect of attenuation at high
frequency, by
sending more bits/Hertz
i.e. can increase bit rate without increasing
signaling (baud) rate
Æ max frequency kept low
Hence attenuation is low and reach is large
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

14. How DSL works ?
Example 1 :
AMI (Alternate Mark Inversion)
Used in T1 systems
Utilization = 1 bit/Hertz
Æ BW = 1544 KHz for 1.544 Mbps
Max distance between repeaters = 1 km
1 1 1 0 0 0 0 1 1 0
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

15. How DSL works ?
Example 2 :
2B1Q (Two binary to One Quat) over 1 pair
Used in ISDN systems
Utilization = 2 bits/Hertz
Æ BW = 784 KHz for 1.544 Mbps
Max reach = 3 km
1 1 1 0 0 0 0 1 1 0
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

16. How DSL works ?
Example 3 :
2B1Q (Two binary to One Quat) over 2 pairs
Used in HDSL (High bit rate Digital
Subscriber Line) systems
Utilization = 4 bits/Hertz over 2 pairs
Æ BW = 392 KHz for 1.544 Mbps
Typical reach = 4.3 km using two pairs
784 kbps
784 kbps
4-wire
HTU-R
4-wire
HTU-C
Customer
Central Office
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

17. How DSL works ?
Example 4 :
CAP (Carrierless Amplitude and Phase
modulation)
Used in symmetric and asymmetric DSL
Utilization = 2 - 9 bits/Hertz
Æ BW = 175 KHz for 1.544 Mbps
Typical reach = 3.6 km - one pair (SDSL/sym)
= 5.5 km - one pair (RADSL/asym)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

18. How DSL works ?
BW for AMI = 4 x BW for 2B1Q = 9 x BW for CAP
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

19. How DSL works ?
Bit rate for AMI and CAP as a function of distance
(symmetric transmission)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

20. How DSL works ?
Other Coding schemes
TC-PAM (Trellis Coded – Pulse Amplitude
Modulation)
Used in symmetric DSL (HDSL2/4, SHDSL)
Utilization = ( 3 info + 1error) bits/Hertz
Approaches theoretical limit of Shannon (by
applying advanced Digital Signal Processing)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

21. How DSL works ?
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

22. How DSL works ?
Other Coding schemes
DMT (Discrete Multi Tone)
Used in asymmetric DSL (ADSL)
Divides spectrum into 256 channels,
each 4 kHz
Within each channel use Quadrature
Amplitude Modulation (QAM)
Utilization = Up to 15 bits/Hertz
Æ Bit rate = 15 x 4 x 256 = 15.36 Mbps (0 length)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

23. How DSL works ?
Other Coding schemes
DMT (Discrete Multi Tone)
Bits
per
Hertz
Bits
per
Hertz
Line
gain
Frequency Frequency Frequency
Due to attenuation, modify # of bits/Hz :
2 or 3 bits/Hz (edge) to 15 bits/Hz (max)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

24. How DSL works ?
• Strategy 3:
Combat effect of crosstalk
NEXT is more significant than FEXT
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

25. How DSL works ?
• Strategy 3:
Combat effect of crosstalk
Method 1 : Reduce # of DSL links on same cable
binder
Method 2 : Use echo canceller to reduce echo
effect of (large) transmitted signal on (small)
received signal. (Valid for crosstalk on same link)
Method 3 : Use different spectrum for transmitted
signal & received signal (i.e. FDM).
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

26. How DSL works ?
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

27. How DSL works ?
Effect of crosstalk greater at Central Office
(more copper loops grouped at Central Office)
Æ downlink signal (from CO to Customer)
can go longer distance than
uplink signal (from Customer to CO)
OR in FDM, place
downlink signal in higher freq. spectrum &
uplink signal in lower freq. Spectrum
(where attenuation is less)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

28. Evolution of DSL Technology
144 kbps/
80 kHz
2B1Q
ISDN
(Early 80’s)
1.544-2.048/
1.544 kHz
AMI/HDB3
T1/E1
(60’s)
-Special conditioned lines
- 1 pair – High costs
- Repeaters every 1-2 km
- Special engineering
- 2 pairs – High costs
Voice
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

29. Evolution of DSL Technology
1.544-2.048/
240-392 kHz
2B1Q
- 12,000 kft (3.7 km)/24 AWG
- 2 pairs
HDSL
(Early 90’s)
T1/E1
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

30. Evolution of DSL Technology
U-stream (CAP):
64 kbps/135 kHz
D-stream (CAP):
1.5 Mbps/1.088
MHz
QAM
CAP
DMT
ADSL
(March 93)
1.544/
175 kHz
CAP
(Early 90’s)
SDSL
(?)
-18,000 kft ( 5.5 km) for 24 AWG - 1 pair
- 11,000 kft ( 3.3 km) for 24 AWG - 1 pair
HDSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

31. Evolution of DSL Technology
128 kbps to
2.048 Mbps
CAP
(8 rates)
M/SDSL
(?)
144 kbps/
80 kHz
2B1Q
ISDSL
(?)
- Automates rate depending on distance
For 24 AWG : 29 kft (8.9 km) at 64 kbps
15 kft (4.5 km) at 2 Mbps
– 1 pair
- Uses proven technology but bypasses switch
- Transmits over copper loops served by DLC
SDSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

32. Evolution of DSL Technology
776 kbps x 2
16 -
TCPAM
HDSL4
(2002)
1.544 Mbps
16 -
TCPAM
HDSL2
(2001)
- Spectrally compatible with HDSL and ADSL
- ANSI standard T1.418
-16 kft (4.9 km) at 24 AWG – 2 pairs
- Spectrally compatible with HDSL and ADSL
- ANSI standard T1.417
-12 kft (3.7 km) at 24 AWG – 1 pair
SDSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

33. Evolution of DSL Technology
192 kbps to 2.312
Mbps (2W)
TCPAM
G.shdsl
128 kbps to 1
Mbps
?
ReachDSL
(1999)
- Spectrally compatible with HDSL and ADSL
- ITU std. G.991.2 – Signaling std. G.944.1
-18 kft (5.5 km) at 24 AWG – 1 pair
- Spectrally compatible with HDSL and ADSL
- Allows voice - Splitterless
- For 24 AWG :18 kft (5.5 km) at 512 kbps –1 pair
SDSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

34. Evolution of DSL Technology
U-stream :
128 kbps- 1 Mbps
D-stream :
1 – 7 Mbps
CAP
RADSL
(?1996)
- Allows rate adaptation based on line conditions
- ANSI std. TR59
- For 24 AWG :18 kft (5.5 km) at 1.5 Mbps
6 kft (1.8 km) at 7 Mbps
ADSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

35. Evolution of DSL Technology
U-stream :
Up to 512 kbps
D-stream :
Up to 1.5 Mbps
DMT
G.lite
(June 1999)
- Lower speed/lower cost variant of ADSL
- Is customer installable
- Can work without splitter, but better to use
microfilter
- Uses “fast retrain”
- ITU std. G.992.2 – 1 pair
ADSL
Bit rate/BW
Modulation
Enhanced
Original
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

36. Evolution of DSL Technology
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

37. Evolution of DSL Technology
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)
Summary of symmetric and asymmetric DSL technologies

38. Evolution of DSL Technologies
Recent Advances :
VDSL (Very High Speed DSL)
Standard under development
Downstream bit rate : up to 52 Mbps
Symmetric bit rate : up to 26 Mbps
Reach at highest bit rate : 1000 ft ( 300 m)
EtherLoop
Proprietary product
D-stream/U-stream bit rate : Up to10 Mbps
Spectrally compatible - Allows voice and data
For 26 AWG, reach > 26 kft
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

39. DSL System Components
Configuration for traditional subscriber loops :
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

40. DSL System Components
Configuration for digital subscriber loops (DSLs) :
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

41. DSL System Components
DSL End Points (DSL Modem/Router)
- End user connections can be :
10BT, 100BT, V.35, T1/E1, ATM
- New ports will support :
RJ 11 ( for Voice over DSL – VoDSL)
USB, IEEE 1394/Firewire for video
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

42. DSL System Components
DSL End Points (DSL Modem/Router)
ADSL Modem
+
Splitter
Tel Line
MDF Blocks
Data + Voice
Data
Voice
DSLAM
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

43. DSL System Components
DSL End Points (DSL Modem/Router)
- End point functionality include :
modulation/demodulation
bridging
routing
TDM multiplexing
ATM multiplexing
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

44. DSL System Components
DSL End Points (DSL Modem/Router)
Æ Bridging uses learning filter to keep
unwanted traffic from traversing network
Æ Routing offer IP support which enables
different users at remote LAN to access
different Network Service providers
Æ TDM endpoints can operate like
DSU/CSUs for traditional T1/E1 service.
Also provide interface to routers, FRADs,
multiplexers, and BPX’s.
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

45. DSL System Components
Splitters and Microfilters
Splitter allows simultaneous POTS and data
services.
Two types : Active, requiring power source
Passive, uses no power source
Two versions : Single channel (1 DSL)
Multiple channel (several DSLs)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

46. DSL System Components
Splitters and Microfilters
Microfilter is a less sophisticated, user
installable component.
A microfilter is either installed for each
faceplate, or one microfilter is used for several
faceplates.
New DSL devices, e.g. G.dmt. ADSL, RADSL,
G.Lie, ReachDSL are spliterless.
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

47. DSL System Components
DSLAM (DSL Access Multiplexers)
1st and 2nd generation DSLAM :
- Aggregates multiple DSL connections,
using PPP and Virtual Private Cicuits
(VPC) of ATM
- Provided “best effort” services
- Not capable of offering multiple services
(e.g. FRoDSL, VPN, VoDSL)
& differentiated levels of Quality of Service
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

48. DSL System Components
DSLAM (DSL Access Multiplexers)
L2 (Layer 2) DSLAMs
DSLAM
ATM Switch
DSL
Termination
CPE
CPE
CPE
CPE
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

49. DSL System Components
DSLAM (DSL Access Multiplexers)
Next generation DSLAM :
- Capable of offering multiple services &
differentiated levels of Quality of Service
by using QoS capability of ATM
- Core has ATM switching fabric (with
possibility for Switched Virtual Circuits)
- Service provider can engineer provisioning
of service to maximize revenue (e.g.
VoDSL or FRoDSL to a business
customer, and “best effort” to a residential
customer)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

50. DSL System Components
DSLAM (DSL Access Multiplexers)
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)
Layer 3 DSLAMs aggregate and terminate
users sessions.
DSLAM
ATM/IP Service
CPE
CPE
CPE
CPE

51. DSL System Components
End-to-End Network Management
Component
Functions :
Adhere to QoS parameters specified in
Service Level Agreement (SLA)
Monitor and measure QoS
parameters, for use by service
provider, as well as by service user
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

52. DSL System Applications
Voice over DSL (VoDSL) Application
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)

53. DSL System Applications
Mahmoud T. El-Hadidi – DSL Workshop – 4 – 6 March , 2003 (Cairo-EGYPT)
Frame Relay over DSL (FRoDSL) Application
(with Service Level Management)