Today's analog modems transmit data at a maximum of 56 kilobit per second (kbit/s). ISDN access is faster at up to 64 kbit/s. But DSL technology promises increased speed and more convenience when using the Internet. DSL stands for "Digital Subscriber Line". What is interesting about DSL is that it uses conventional telephone copper pairs to support high-speed data communications; no new cables need to be laid on the user's premises.
Analog telephone traffic over a copper pair occupies frequencies up to 4 kHz - in theory, however, this type of channel allows frequencies up to 1.1 MHz to be used. By dividing the bandwidth into various channels, for voice and data, for example, and using the higher frequency bands that have not been used in the past, DSL technologies increase data rates over copper wires to up to 52 megabits per second (Mbit/s). In practice however, reduced transfer rates tend to be used to keep any mutual interference within the cable sections to a minimum. An important parameter for DSL technology is the distance between the exchange, in other words the network node, and the DSL user. The shorter the distance, the higher the data rates that can be supported over the DSL access. The structure of Deutsche Telekom's network is ideally suited to using DSL technology.
DSL variants There are several different DSL variants, for example HDSL, IDSL, RADSL and CDSL. Most widespread are ADSL and SDSL, with the A standing for "asymmetric" and S for "symmetric" respectively.
ADSL ADSL was originally developed as a transmission system for video-on-demand. With ADSL, the speed of the data stream to the ADSL user, in theory up to 6 Mbit/s, is significantly higher than in the opposite direction (768 kbit/s). ADSL is the perfect solution particularly for Internet communications where large amounts of data need to be downloaded from the Web while much less data, possibly in the form of control commands, is uploaded. With the aid of an upstream filter, the so-called splitter, the frequency band is divided into subbands with different bandwidths while the voice communications are separated from high-volume data applications. Another key consideration for customers is that channels earmarked for telephone and fax applications are retained. DSL technology means the customer receives an additional data channel on the same line.
SDSL Unlike ADSL, SDSL supports data rates of up to 2.3 Mbit/s over the same copper pair - symmetrically, in other words in both directions, upstream and downstream. SDSL is used with broadband applications such as links between local area networks, intranet applications, videoconferencing, telelearning and web hosting. Deutsche Telekom will be using CeBIT to unveil its first symmetrical DSL product, BusinessOnline SDSL.
T-DSL T-DSL is Deutsche Telekom's ADSL solution. Supporting data rates of up to 768 kbit/s from the Internet to the PC and up to 128 kbit/s from the PC to the network, the Internet connection represents a twelve-fold increase over ISDN speeds when using a single channel to download data from the Web. Scheduled for release in the fall, T-DSL 1500 should support downstream rates of 1.5 Mbit/s and upstream rates of 192 kbit/s.
To take advantage of this high-speed technology, you will need:
- A Deutsche Telekom access (T-ISDN or T-Net) and an installed T-DSL line,
- an Internet service provider that supports T-DSL (for example T-Online),
- a PC with a network card (Ethernet) or an external Ethernet USB adapter and
- a DSL modem (available from Deutsche Telekom). Certain models do not require a network card.
T-DSL via satellite For customers who do not have high-speed Internet access via T-DSL over the fixed network, Deutsche Telekom will be offering T-DSL via satellite from the beginning of May 2002. All you will need is a Deutsche Telekom fixed line, Internet access, for example via T-Online, a DVB card for your PC and a digital satellite receiver.
System requirements The computer should support the following system requirements:
- Pentium II 233 MHz or equivalent processor as a minimum, with at least 64 MB RAM; Pentium III 500 MHz or a comparable processor as a minimum is required to receive TV on a PC
- Operating system: Windows 95, 98, ME or 2000
- Free PCI 2.1 slot or USB port
- Modem or ISDN card
- CD-ROM drive
- 30 MB available disk space
- Microsoft Explorer 5.x or higher, or comparable browser
- Direct Draw-compatible PCI or AGP graphics card (with hardware video overlay)
- DirectX 7 or higher
- PCI soundcard
Hardware installation
To use T-DSL, you will need a T-DSL splitter and a T-DSL modem along with an Ethernet card for your PC. The T-DSL splitter separates the T-DSL signals from the telephone signals while the T-DSL modem provides high-speed Internet access. Depending on the local configuration (T-Net or T-ISDN, with or without PABX, etc.), various options exist for installing these components and integrating them into existing inhouse cabling.
Helped by configuration agents on Deutsche Telekom's homepage, customers have access to full installation instructions that are geared to their own specific situation. Examples of how to fit the Ethernet card and install the software on the PC along with general information on how to assemble the splitter and modem can be found in the Flash operating instructions that are also on Deutsche Telekom's homepage. T-DSL installation and functional tests can also be downloaded from the homepage, thereby ensuring installation is simple - if there is a problem with the installation, the program helps with troubleshooting. And once you have installed T-DSL, the speed manager optimizes the operating system to give you the highest possible speeds; it also always displays the current transmission speed. Both programs can be found under T-DSL Software & Downloads on Deutsche Telekom's homepage.