The Network Element (NE) supports multi-ADSL subscriber lines. This section
provides some explanation on the different supported ADSL flavours and ADSL
bonding.
Asymmetric Digital Subscriber Line
The Asymmetric Digital Subscriber Line (ADSL) system is used on existing metallic
twisted-pairs (one per user) between the Customer Premises Equipment (CPE) and a
Central Office (CO) exchange.
A Frequency Division Multiplexing (FDM) technique allows the simultaneous use
of high-speed data services and the existing (lifeline) Plain Old Telephone Service
(POTS) or Integrated Services Digital Network (ISDN).
Other advantages of ADSL are:
• The existing cable network is used by the network operator (reducing costs).
• The existing telephone service, including equipment, is retained by the customer.
Asymmetric nature of ADSL
The digital transmission capacity of the ADSL system is asymmetric in the sense that
the downstream and upstream bit rates are different:
• The downstream bit rate can range from 32 kb/s up to 8 Mb/s. The bit rate
granularity is 32 kb/s.
• The upstream bit rate can range from 32 kb/s to 1 Mb/s. The bit rate granularity
is 32 kb/s.
The chosen rate depends on the bi-directional services to be supported and the loop
characteristics.
This method allows high bandwidth services, for example, digital audio and video
(multimedia), Ethernet interconnection to the customer, and so on.
Bidirectional transport
With ADSL, the transport system provides bidirectional asymmetric communication
over a single or double twisted-pair without repeaters.
ADSL services
The multi-ADSL mode and maximum physical bit rate is automatically determined
during initialization of the modem based on line conditions. Modem initialization is
done using a predefined noise margin and within the constraints of the transmit
power spectral density. The service management system then sets the line rate to the
correct value. This is done according to the customer service profile and maximizes
the noise margin and/or minimizes the transmission power. This allows various
levels of service, for example, offering the highest bit rates at a premium or ensuring
a guaranteed bit rate. Bit rates can be selected linearly, up to the maximum rate
possible. Each individual user can have different bit rates.
Operational modes
Table 1-1 lists the ADSL operational modes supported by the multi-ADSL boards
Table 1-1 ADSL operational modes
Operation Mode Description
T1.413 Issue 2 ANSI standard (ADSL ansi)
DTS/TM-06006 ETSI standard (also called “ETSI ISDN”)
G.992.1 Annex A (Also known as G.DMT. Operation over POTS non-overlapped spectrum
G.992.1 Annex B Operation over ISDN non-overlapped spectrum
G.992.2 Annex A Also known as G.lite. Operation over POTS non-overlapped spectrum.
This standard is a medium bandwidth version of ADSL that allows Internet
access at up to 1.5 megabits downstream and up to 512 kilobits upstream
