Introduction to ADSL Technology. by: Wenmei Zhao May 3, 1999. ADSL — What is it? Why ADSL? ADSL Family Features ADSL vs. cable modem System Model Channel Modeling. Noise Echo Canceller Line Codes DMT CAP Frame Structure Bell Atlantic ADSL References. Outline. ADSL — What is it?.
by: Wenmei Zhao
May 3, 1999
Secure. “Point to point connectivity” of ADSL ensures the security of the service. Cable, by contrast, is shared media and is not secure at all.
Bigger coverage area.
Cheap. ADSL uses existing twisted pair, hence is cheap in installation and also cheap in monthly payment.
Bandwidth. ADSL has about 1.1MHz BW due to loop limitations, while cable modem has about 745MHz BW.
Bridge taps, DLCs, load coils can lead to problems.
Mutual noise among different DSL lines, T1 lines.ADSL vs. cable modem
There are three main types of noise that affect
DSL system performance:
A simplified NEXT model for N disturbers:
A simplified FEXT model for N disturbers:
Two main contenders:
PSD of DMTPSD is useful for finding received signal power, thus useful for analyzing NEXT and FEXT noises.Upstream and downstream PSD models are:
A super frame is defined for every 68 IFFT/FFT
operations.The super frame has a time duration
of 68/4k=17ms for baud rate of 4kHz.
Product Speeds Price Loop Qual.
Infospeed640k d:640 kbps $39.95 12,000ft.
Infospeed1.6M d:1.6 Mbps $59.95 8,000-12,000ft.
Infospeed7.1M d:7.1 Mbps $109.95 8,000ft.