DSL filter

A DSL Soft, also ( DSL ) Splitter ( engl. to split: split, split ) or BBAE ( Broadband Access Equipment, broadband connection unit) called, is a device that the frequencies of phone and DSL, which together via a subscriber line (TAL ) are transmitted, splits in the receive direction and merges in the transmit direction. The DSL Soft is required at both ends of the subscriber line.

Features and Functions

Seen in electrical engineering is a high-speed switch, a crossover. The high-pass filter component to connect the DSL modem is executed only rudimentary as capacitive coupling (one capacitor 27 nF and 400 V series in the two lines leading to the DSL modem ), while the low-pass filter circuit for connection of conventional fixed-line devices or ISDN NTBAs is realized much more complex.

In Germany is used for ISDN connections to the TAL ( UK0 interface) of 4B3T line code, so that the frequencies between 0 and 120 kHz are occupied. Frequencies above 138 kHz can then be used for DSL (Annex B ). For analog telephone connections usually only frequencies below 25 kHz are used, therefore frequencies from about 25 kHz ( channel 6) from a technical perspective be used for DSL (Annex A ), which can be greater ranges and data transfer rates achieved. For the sake of mass production, the simpler operation and maintenance and in particular marketing reasons ( less favorable treatment of ISDN) DSL ​​only way for Annex B are used for analog and digital telephone connections in Germany from Deutsche Telekom. Outside Germany and Slovakia, however, anywhere broadband turnout for Annex A are used on analog lines.

In the local exchange switch the DSL is not running as a separate device, but circuitry integrated on the circuit board of a DSLAM or permanently installed as a so-called MDF integrated splitter in the main distribution.

An analog connections outside Germany a different frequency filters topography instead of the here discussed DSL -soft technology common: There is a high-pass filter in front of the DSL modem connected, or this is already integrated in the modem, and analog before each (usually parallel to the modem connected ) terminal is switched to a low-pass filter. This frequency filter of installation is also on analog lines in Germany possible ( a DSL switch can also be used as a simple low-pass or high-pass filter ), but it may have because of generated thereby spurs a reduced quality of the DSL signal to a row.

A circuit diagram for a DSL splitter can be found in Figure 5 of U.S. Patent No. US6728367. By now, low-input filter circuits for VDSL requirements.


There are the following three sockets at a German high-speed switch:

  • An RJ jack for connection to the telephone jack using the supplied cable (as in the NT ), in which the contacts 1 and 6 with Office a / b are occupied. If the provided TAE cable is too short, instead, a longer cable installation and used directly to terminals office a / b are clamped on the splitter. It should then be used with twisted wires, a cable, a longer flat cable must be avoided.
  • A TAE NFN jack for connecting analog telephones, fax machines, answering machines, and modems.
  • An " RJ-45 " connector ( modular jack 8P2C ), in which the contacts 4 and 5 are assigned with high speed a / b.

Alternatively, a connection is possible directly to the terminal block:

  • Office a / b is the receipt of the official line ( local loop ), these terminals are parallel to the RJ socket Note: If the splitter directly connected to the subscriber line and thereby takes the first TAE function, care should be taken that there is a model with integrated passive Inspection itself (PPA ) and this is on, since without it a line test at a interference is not possible
  • La and Lb: If you created any AMT line to the DSL Soft, La and Lb can be used as inputs to the telephone socket of the DSL Soft
  • If the AMT line in use, it usually ranges from to connect the analog devices via the terminals La and Lb
  • If analog devices connected simultaneously via both telephone sockets DSL Soft and via the terminal strip, terminals should be there to avoid a parallel circuit instead be used a2 and b2
  • When plugged into the telephone socket of the DSL switch a telephone ( F connector ), please note that thus the contacts to a2 and b2 are interrupted and all participants are no longer reachable from a2 and b2. Only devices with an N connector can be plugged into the telephone socket of the DSL Soft only if other devices to be connected to a2 and b2, because devices with N connector (eg fax or analog modem ) the contacts internally in standby mode even bridges and opens only when active.
  • The DSL-a/b-Anschlüsse the DSL Soft are ( socket pin 4 and 5 of the " RJ- 45 " ) associated with the middle contacts with the router and back
  • The connection between the DSL router and back Soft and should be made with a twisted pair cable ( twisted pair )
  • Untwisted telephone flat cable are to be avoided for reasons of electromagnetic compatibility necessarily
  • In a star quad two opposite strands form a pair

For a phone function, it is irrelevant whether a DSL Soft is installed. Neither an installation of DSL Soft time before broadband provision nor its absence after the DSL deployment affect the operation of an analog or ISDN telephone line.