DSL – Broadband Technology

DSL

DSL - Digital Subscriber Line Technology is a copper loop transmission technology that achieves broadband speeds over the most universal network medium in the world – ordinary telephone line. DSL Technology is widely used most of countries because of its rich feature. Internet demand is growing rapidly year-on-year where every telco wanted to provide Internet as services to their customer and DSL is the best technology through which Telco can provide Internet to their customer using existing copper wire.    

• Asymmetric – The data can flow faster in one direction than the other. Data transmission has faster downstream to the subscriber than upstream
• Digital – No type of communication is transferred in an analog method. All data is purely digital, and only at the end, modulated to be carried over the line.
• Subscriber Line – The data is carried over a single twisted pair copper loop to the subscriber premises.

ADSL standards:

ADSL Range – As distance decreases toward the telephone company office, the data rate increases. In general, the maximum range for DSL without a repeater is 5.5 km and ADSL other speed factors are – type and thickness of wires used, number and type of joins in the wire, proximity of the wires to radio transmitters.

ADSL network components –

• The ADSL modem at the customer premises (ATU-R) – Session initiate.
• DSL access multiplexer (DSLAM) -
• Broadband Remote Access Server (B-RAS) – Remote session termination point.
• Splitter – an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM.

DSL Modulation-Discrete Multi Tone-DMT -

• DMT has 224 downstream frequency bins and up to 31 upstream bins
• Up to 15 bits per symbol can be encoded on each bin on a good quality line.
• Uplink Speed = (15* 4.3125*31) = 2 Mbps
• Down link Speed = (15* 4.3125*224) = 14.49 Mbps

PPP Broadband Access Methods –

• PPPoA – PPP session initiated by CPE
• PPPoE– PPP sessions initiated by the client