Explain the procedure of DSL Internet Access

Problem is:

Explain the procedure of DSL Internet Access.

Solution is:

DSL Internet Access:
Today, the two most prevalent types of broadband residential access are Digital Subscriber Line (DSL) and cable.

A residence typically obtains DSL Internet access from the same local telephone company (telco) that provides its wired local phone access. Thus, when DSL is used, a customer’s telco is also its ISP. As shown in Figure, each customer’s DSL modem uses the existing telephone line to exchange data with a digital subscriber line access multiplexer (DSLAM) located in the telco’s local central office (CO).



The home’s DSL modem takes digital data and translates it to high frequency tones for transmission over telephone wires to the CO; the analog signals from many such houses are translated back into digital format at the DSLAM.

The residential telephone line carries both data and traditional telephone signals simultaneously, which are encoded at different frequencies:
• A high-speed downstream channel, in the 50 kHz to 1 MHz band
• A medium-speed upstream channel, in the 4 kHz to 50 kHz band
• An ordinary two-way telephone channel, in the 0 to 4 kHz band

This approach makes the single DSL link appear as if there were three separate links, so that a telephone call and an Internet connection can share the DSL link at the same time.

The The DSL standards define transmission rates of 12 Mbps downstream and
1.8 Mbps upstream [ITU 1999], and 24 Mbps downstream and 2.5 Mbps upstream [ITU 2003].

Because the downstream and upstream rates are different, the access is said to be asymmetric.
While DSL makes use of the telco’s existing local telephone infrastructure, cable Internet access makes use of the cable television company’s existing cable television infrastructure.

A residence obtains cable Internet access from the same company that provides its cable television. As illustrated in Figure 1.6, fiber optics connects the cable head end to neighborhood-level junctions,

from which traditional coaxial cable is then used to reach individual houses and apartments. Each neighborhood junction typically supports 500 to 5,000 homes.

Because both fiber and coaxial cable are employed in this system, it is often referred to as hybrid fiber coax (HFC).
One important characteristic of cable Internet access is that it is a shared broadcast medium. In particular, every packet sent by the head end travels downstream on every link to every home and every packet sent by a home travels on the upstream channel to the head end.




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