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Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. [1] In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.
Today, the most common trellis-modulated V.34 modems use a 4-dimensional set partition—achieved by treating two two-dimensional symbols as a single lattice. This set uses 8, 16, or 32 state convolutional codes to squeeze the equivalent of 6 to 10 bits into each symbol the modem sends (for example, 2,400 baud × 8 bits/symbol = 19,200 bit/s).
If bit swapping is disabled then this does not happen and the modem needs to retrain in order to adapt to changing line conditions. There are 2 competing standards for DMT ADSL - ANSI and G.dmt; ANSI T1.413 is a North American standard, G.992.1 (G.dmt) is an ITU (United Nations Telecom committee) standard.
The 201A Data-Phone was a synchronous modem using two-bit-per-symbol phase-shift keying (PSK) encoding, achieving 2,000 bit/s half-duplex over normal phone lines. [10] In this system the two tones for any one side of the connection are sent at similar frequencies as in the 300 bit/s systems, but slightly out of phase.
For this two-pair 2B1Q variant of HDSL, framing increases the bitrate from 1.544 Mbit/s to 1.568 Mbit/s, resulting in a symbol rate of 392 kilobaud and a Nyquist frequency of 196 kHz. Legacy T1 required repeaters every 35 dB of attenuation, equivalent to 1 to 1.2 miles (1.6 to 1.9 km), [ citation needed ] depending on conductor gauge and other ...
For example, the sample diagram does not indicate the physical type of connection between the PCs and the switch, but since a modern LAN is depicted, Ethernet may be assumed. If the same style of line was used in a WAN (wide area network) diagram, however, it may indicate a different type of connection.
DSL routers, the most common form of DSL modem, are external to the computer and wired to the computer's Ethernet port or its USB port, whereas voice-band modems are usually internal devices installed in the computer itself in a PCI interface slot in the back. Internal DSL modems are rare but available.