ADSL Modems
Network Architecture and Physical Connectivity
ADSL architecture is made up of the following components:
Splitter & Micro-Filter
As was mentioned earlier, in ADSL the data and the voice are transmitted on the same twisted pair of the phone wire. The voice (POTS) is transmitted on the low frequencies and the ADSL data on the high frequencies.
The splitter contains a micro-filter, which prevents the ADSL data channel and the voice channel from interfering with each other. In the transmit direction, it receives the two channels and combines them to a single channel, with the frequency division as described earlier in this chapter.
In the receive direction, the micro-filter separates the two channels with a low/high pass filter, and then sends each of the two signals to different wires. The voice channel (POTS) goes to an E1/T1 connection to the PSTN, and the ADSL channel goes to a DSLAM.
DSLAM
Acronym of Digital Subscriber Line Access Multiplexer. The DSLAM receives ADSL lines from different subscribers, and multiplexes them into ATM virtual circuits.
The DSLAM contains an ADSL modem for each of the subscribers that are connected to it. After the ADSL signals from all the subscribers are demodulated into digital data, it is combined and sent onto a high-speed interface connected to an ATM network.
This ATM network provides access to the internet through internet service providers (ISPs). The DSL provider bundles the traffic destined for a given ISP and sends it over an E3/T3 or an OC-3 connection.
ADSL Modems
Network Architecture and Physical Connectivity