ADSL and CATV: High-Speed Internet Technologies
Dedicated Access Lines and Terrestrial Communications
Dedicated access lines are lines that are active at any time, providing an “always online” solution with permanently available transmission capacity.
Characteristics of Terrestrial Communications Networks
ADSL over ISDN and PSTN, implemented in our country, allows for the expansion of bandwidth, access speed, and the number of services. Another major form of terrestrial communication is via the networks of cable operators, initially used for cable television in households. However, they have expanded to include telephony and telematics services, especially Internet access.
On the other hand, Power Line Communication (PLC) is gaining traction. This technology, still being tested, uses electrical lines to carry data signals to central hubs. Power companies are exploring this new source of income through their telecommunications subsidiaries.
Asymmetric Digital Subscriber Line (ADSL)
Each of the xDSL technologies, both symmetric and asymmetric, has different characteristics in terms of performance (data transmission speed) and maximum distance from the central office. This is because copper wire was not originally designed for this purpose. Of all these, ADSL is the most suitable for domestic use.
ADSL uses a range from 24 KHz up to 1104 KHz for transmitting data signals in both directions. It has three channels:
- One conventional channel (0-4 KHz) for voice calls.
- One channel for sending data (160-1104 KHz), called the user direction or upstream.
- One channel for receiving data (160-1104 KHz), called the network direction or downstream.
ADSL basically consists of four elements:
- The remote terminal unit (an ADSL modem located in the user’s home).
- The central terminal unit (an ADSL modem located in the customer’s central office).
- The user’s splitter (splits the received signal into two: one for conventional telephone (voice) and one for ADSL (data)).
- The central splitter (separates the signal, sending voice to the PSTN and transmitting data through a separate network).
ADSL: Maximizes the current loop of twisted-pair copper to create a high-speed digital line, achieving faster speeds and becoming known as a broadband Internet connection.
Splitter: A device that separates signals using two filters:
- Low Pass: Allows low-frequency signals (voice calls) to pass through.
- High Pass: Allows high-frequency signals (ADSL data) to pass through.
Cable TV Networks (CATV) for Internet Access
Cable TV (CATV) networks are another technology used today for broadband Internet access, often referred to as “cable.” Operators invest in building their own fiber optic backbone and coaxial cable loops, unlike ADSL, which utilizes existing infrastructure.
Besides Internet access, the same cable carries signals for a large number of TV channels and may also include phone signals. Typically, three packages of services are offered to customers in a triple play offer (voice, data, and television).
Essentially, a cable modem is connected to the coaxial jack installed by the operator. This connects to a Cable Modem Termination System (CMTS). The user’s PC connects through an Ethernet RJ45 port. This type of connection provides higher speeds compared to conventional modems.
Downstream speeds (from the Internet to the user) can reach 40 Mbps, while upstream speeds (from the user to the Internet) can reach 10 Mbps. A major advantage is that it frees up the phone line, as all communication is done through the CATV service cable. The main disadvantage is that all users share the network cable and bandwidth, potentially leading to speeds lower than those contracted.
Cable: Leverages CATV networks of fiber optic and coaxial cable to create a high-speed digital data transmission line.
CATV: Leverages television networks of fiber optic and coaxial cable to create a high-speed digital data transmission line.