The
radical technological changes in
the telecommunications sector have
recently led to the development
of the DSL technology (Digital
Subscriber Line) and in general,
the xDSL family. The DSL technology creates a unique
opportunity to maximise the utilisation of copper
infrastructure and enable broadband service delivery.
DSL technology offers the possibility of delivering
both narrowband services (POTs and ISDN-Basic Rate
Access) and broadband services on the same copper
pair. The distinction between narrowband and broadband
services is the transmission rate required for the
service.
Specifically, the ADSL technology (Asymmetric DSL)
utilises methods of digital encoding and signal processing,
in order to increase the capacity of the traditional
twisted copper pair. ADSL uses a spectrum which reaches
up to approximately 1MHz, whilst avoiding at the lower
end the use of baseband frequencies which are occupied
by traditional narrowband services. The clear distinction
of the two spectra, as demonstrated in Figure 1 , enables
the separation of broadband services delivered over
ADSL and narrowband services by simply installing a
splitter, or distributed filter, at both ends of the
copper line. For info rmation regarding the installation
of the splitter and rewiring at the customer premises
please refer to Installation
Instructions.
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Figure
1:
ADSL Power Spectrum |
ADSL technology is asymmetrical: It transfers
data at higher speeds to the customer (downstream) than from
the customer to the Central Office (upstream). The maximum
transmission rates can reach up to 8Mbit/s downstream and
640kbit/s upstream. The transmission rate depends on the
attenuation suffered by the signal (mainly due to the length
and diameter of the copper line), as well as on the crosstalk
and noise interference in the cable.
With the above characteristics, the ADSL has the capability to transfer simultaneously
voice, data (including internet traffic) and video with high quality and fidelity.
Figure 2 , shows a schematic view of the maximum speed offered
with various copper-line access technologies and the time required transferring
a 25Mbyte file.
 |
Figure
2:
Shows a schematic view of the maximum speed offered
with various copper-line access technologies and the
time required transferring a 25Mbyte file. |
Figure 3 , shows the traditional
way of connecting a Personal Computer to the Internet Service
Provider using an analogue modem and the Public Switched
Telephone Network. Figure 4 , shows the
new connection using an ADSL modem and a splitter at the
customer site. Services are being transferred over the broadband
core network.
Figure 3
Figure 4
In order
to be able to deliver i
-choice services,
it is a fundamental requirement
that the Central Office or
Local Exchange site at which
the customer is being connected
(with a copper pair) is equipped
with the Digital Subscriber
Line Access Multiplexer (DSLAM) .
Sites at which DSLAMs are installed
and service is available can
be found under i-choice Availability.
Further information regarding
ADSL technology may be found
on the web page http://www.adsl.com/dsl_forum.html
The i-choice category of services
may be offered using three
different types of ADSL modems:
modems with USB, 10BaseT and ATMF25.6 interfaces.
At least one of these types of interface must be available
in the Personal Computer (PC) to
which the modem is attached. For example, if the PC
has a USB interface, then it
is recommended that a USB type
of modem be used. In case the
PC is equipped with an Ethernet
card, then it is recommended
that a modem with a 10BaseT interface
be used.
The i -choice 2 service
can be offered using only the 10BaseT (Ethernet) interface.
Also, there are ADSL modems with an internally integrated
router. This kind of modems shall be offered in the
case where the service requested is the i
-choice business . The
type of interface to this kind of ADSL modem/routers
is the 10BaseT .
The ADSL modems, which support coexistence of analogue
telephone services (POTs), are different than the ones
that support coexistence with digital telephony (ISDN-Basic
Rate Access).
You may find further information on the installation
of modems in this web page under the heading Installation
Instructions, as well as in the user manuals, which
are provided with the ADSL modems.
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