Two
basic standards for ADSL realization are DMT (Discrete
MultiTone), which is used in our country, and CAP
(Carrierless Amplitude/Phase) system. DMT
system is based on distribution of frequency ADSL
channel into 274 smaller independent channels of
4 KHz. Every individual channel contains a group
of data, as if there is 274 modems connected to
your PC, as shown in figure 1.
Figure 1. View of ADSL frequency
spectrum
Realization is
from user's side based on using micro filter whose
goal is to separate two frequency ranges. The
first frequency range serves for using telephone
line without changing previous telephone number
and without keeping it busy while you are on-line,
as shown in figure 2. The second frequency range
is used for data transfer. Frequency range from
0 to 4 KHz is used for voice transfer, the second
range from 20 to 160 KHz is used for upstream,
and the range from 240 to 1100 KHz for downstream.
Figure2. Present situation
Filter with these
characteristics is intended for users with classic
telephones (Anex A) - POTS (Plain Old Telephone
Service), and Anex B category micro filter is
intended for users with ISDN line (because ISDN
line has frequency range from 0 to 80 KHz). Also,
you have to choose an ADSL device (Anex A or Anex
B) according to this.
Figure 3. View of home ADSL installation
Figure 4. Technical view of
ADSL solution
As far as Internet provider
is concerned, the thing is a bit more complicated.
First of all, the signal coming from you is separated
by micro filter into voice signal, which is forwarded
to the telephone exchange, and the second signal
for ADSL, which ends in DSLAM (DSL Access Multiplexer).
DSLAM receives all ADSL connections and forwards
them to ATM network. DSLAM is the main collector
for every telephone exchange. ATM network is used
as the transport network.
ATM packages are forwarded to BRAS
(Broadband Access Server). BRAS is used for transferring
packages from ATM network to IP package network.
These delivered IP packages end up on BeotelNet
servers from where they are distributed to the Internet,
as shown in figure 4.
