Asymmetric Digital
Subscriber Line
Driving force:
The ADSL Forum
Getting 10MB/s to homes, using telephone lines
Formal education is often times misleading!?
Who wins:
Discrete MultiTone (DMT)
or
Carrierless Amplitude/Phase (CAP)?
Success story: Bay Networks
BROADBAND APPLICATIONS
Entertainment |
Broadcast TV |
6 Mbps |
TV |
|
VOD |
3 Mbps |
TV |
|
Internet-Text |
0.014-6 Mbps |
PC/NT (TV) |
|
Internet-Graphics |
0.5-6 Mbps |
PC/INT (TV) |
|
Gambling |
0.014-2 Mbps |
PV/NT/TV |
|
Games |
0.014-16 Mbps |
PC/NT/TV |
|
|
|
|
Consumer |
Shopping |
0.5-6 Mbps |
PC/NT/TV |
|
Education |
0.5-6 Mbps |
PC/NT |
|
Education |
1.5-6 Mbps |
TV |
|
|
|
|
Professional |
Work at Home |
0.014-6 Mbps |
PC |
|
SOHO |
0.014-6 Mbps |
PC |
|
Video Conf |
0.128-1.5 Mbps |
PC |
NT = Network Terminal (aka Gutless PC)
PC HOUSEHOLDS
ADSL CONFIGURATION
SPEED SHRINKS WITH DISTANCE
DSL BROADBAND TECHNOLOGIES
HDSL |
1.5/2.0 Mbps symmetric |
|
|
SDSL |
1.5/2.0 Mbps symmetric |
|
|
ADSL |
1.5-9.0 Mbps, asymmetric (640 max upstream) |
|
|
VDSL |
Current View 13-52 Mbps, asymmetric (3 Mbos upstream) |
DSL = Digital Subscriber Line, H = High, S = Single line, A = Asymmetric, V = Very high rate
LINE CODES
Two general alternatives in marketplace today
QAM/CAP-single carrier (like voice band modems)
10,000 in field trials
Helped prove ADSL concept
DMT-Discrete MultiTone
ANSI standard
1000 in field trials
Helped prove ADSL to 6 Mbps
DMT OR CAP?
Both will work.
But cannot be made to interoperate
DMT Benefits: |
32 kbps rate granularity (CAP at 320 kbps) Probably works on more lines |
|
|
CAP Benefits: |
Dominated field trials to date |
With equal levels of integration, complexity and power appear comparable.
Time is of the essence in the market
Stay tuned!
DSL: A POINT-TO-POINT SOLUTION
ATU-C = DSL modem in the CO
ATU-R = DSL modem at the service subscriber's premises
* Network interface: DSL equipment on both sides of the link (i.e., both the ATU-R and
ATU-C) have network interfaces to connect to the access provider's and customer's
networks. These interfaces may include Ethernet, Fast Ethernet, ATM, T-1/E-1, ISDN,
Frame Relay, or others
TWO-DIMENSIONAL LINE ENCODING
BIT MAPPING CONSTELLATIONS
FOR A TWO-DIMENSIONAL LINE CODE
AND 64-CAP
UPSTREAM AND DOWNSTREAM
CHANNELS IN CAP SYSTEMS
CAP TRANSCEIVER ARCHITECTURE
DMT'S UTILIZATION
FREQUENCY SPECTRUM AVAILABLE ON A SINGLE TWISTED PAIR WIRE
(I.E., TELEPHONE CABLE)
DMT TRANSMITTER AND RECEIVER
ARCHITECTURES
MYTH VS. REALITY
Myth |
Reality |
|
|
|
|
|
|
|
|
|
|
|
|
ADSL modems versus cable modems:
Cable - 3Mbps (popular rate)
ADSL - 9Mbps/downstream and 1Mbps/upstream (popular rates)
Issues in cable technology (speed and price):
Getting faster and less expensive (better SNR, economies of scale, ...)
IEEE 802.14 (cable TV metropolitan area network standard)
Issues in ADSL technology
(very high speeed versus universal):
Orckit Communications offers very high speed DSL (52Mbps vs 13Mbps)
Microsoft (2000) Comcast $1B investment for UADSL (1.5Mbps vs 512Kbps)
Comparative dissadventages of ADSL:
a. A 4KHz splitter needed to separate voice from ADSL (not if cable used)
b. I-structure additions less widespread (modifications needed in PBX)
c. More expensive ($40 to $80 vs $40 = analog modem + second line)
d. More attractive for business (traditional experiences of phone companies)
Comparative adventages of ADSL:
a. Sending a fixed number of packets in time (not when bandwidth available)
b. Less security risks (interference can be an issue in cable technology)
c. All ADSL i-structure can transmit upstream (only 20% cable-i-structure)
d. All homes and businesses have phone lines (cable: H=60% and B=20%)
Reference:
Lawton, G., Paving the Information Superhighway's Last Mile,
IEEE Computer, April 1998, pp. 10-14.
Research at UB/IFACT
1. DMT and VLSI
2. The story of HFM
Getting repeated once every decade! IEEE Trans/ASSP
3. The story of GaAs
Ranking changes when technology changes! IEEE Trans/Computers
Acknowledgments:
Dejan Raskovic, ...