Asymmetric Digital Subscriber Line 2
Asymmetric Digital Subscriber Line 2 ( ADSL2 ) and Extended bandwidth Asymmetric Digital Subscriber Line 2 ( ADSL2 + ) are further developments of the ADSL standard ( G.992.1 / G.992.2), which primarily improve the data rates and range of an ADSL connection. The improvement in range allows the network operator to offer ADSL to a larger number of potential customers, while the higher data rates enable new services such as high definition television ( HDTV ) via an Internet connection.
ADSL2 and ADSL2 + have been standardized as G.992.3 and G.992.5 by the ITU .
Differences to ADSL
With ADSL , the maximum receive data rate ( downstream ) is 10 Mbit / s and the maximum send data rate ( upstream ) 1 Mbit / s, with the G.992.1 standard with Annex A and Annex B.
- ADSL2
With Asymmetric Digital Subscriber Line 2 (ADSL2), improved signal processing and coding lead to higher relative data rates for a given distance compared to ADSL. ADSL2 has a power-saving function ( L2 mode ) when no data is being transmitted, as well as the so-called seamless rate adaptation . For ADSL2, the maximum data rates are 12 Mbit / s in the downstream and 3.5 Mbit / s in the upstream , for the G.992.3 and Annex J.
- ADSL2 +
Extended bandwidth Asymmetric Digital Subscriber Line 2 (ADSL2 +) extends the bandwidth of the ADSL signal from 1.1 MHz to 2.2 MHz and thus increases the maximum data rate to 24 Mbit / s in the receiving direction and 3.5 Mbit / s in the sending direction, for the G.992.5 standard with Annex J. In Germany, with the exception of some locally available offers, only max. 16 Mbit / s offered in the receiving direction. ADSL2 + also has the L2 power saving function and Seamless Rate Adaptation .
Compatibility with ADSL
While an ADSL2 / 2 + connection is being established, the modem and the exchange exchange information about the capabilities of the other side, so both ADSL2 / 2 + modems in a pure ADSL network and ADSL modems on an ADSL2 / 2 + Line (the latter does not, however, apply to ADSL2 + connections of Deutsche Telekom).
ADSL2 / 2 + variants
With Reach-Extended-ADSL2 (RE-ADSL2; ITU G.992.3 Annex L ), a transmission variant for particularly long connection lines with simultaneous possible analog telephony has been standardized, in which the transmission level is raised in the lower frequency ranges, so that the one that can be supplied with an ADSL exchange Area compared to ADSL-over-POTS ( Annex A ) is increased by around 40%. France Telecom has been using RE-ADSL2 across the country for long access lines since spring 2006.
In order to accommodate companies that usually have a higher outgoing data volume than average consumers, variants of the ADSL2 were introduced with ITU G.992.3 / 5 Annex M (with simultaneous analog telephony) and ITU G.992.3 / 5 Annex J (for unbundled DSL ) / 2+ standards were created that increase the maximum data rate in the sending direction (i.e. into the network) to up to 3.5 Mbit / s.
Due to the identical up / downstream frequency split at 276 kHz, these variants have high spectral compatibility with the ADSL-over-ISDN ( Annex B ) used exclusively in Germany , which is why they are used by Deutsche Telekom in contrast to Annex A and Annex L. have been approved in their valley network for several years; Regardless of this, there were still no offers based on it on the German market in summer 2009. At Deutsche Telekom, consideration was given to using Annex J instead of Annex B for all-IP connections . In the meantime (as of November 2011) there are already connections implemented via Annex-J that also do not require a forced disconnection.
Outside Germany, on the other hand, DSL access based on Annex M has been offered for several years, for example by the Australian provider Internode , the British provider Be * , the Danish provider Fullrate and the Swedish provider Bredbandsbolaget (20 Mbit / s downstream, 3 Mbit / s upstream) .
In Japan, another variant of ADSL2 +, which has not yet been standardized, is used, which expands the reception spectrum to 3.7 MHz and enables data rates of up to 50 Mbit / s. With these high data rates, ADSL competes with VDSL , with the advantage of being able to establish a connection even when the subscriber is far from the exchange.
In addition, with ADSL2 / 2 + - as previously only with SDSL - it is possible to bundle several copper pairs by means of bonding at the DSL protocol level to increase the data rates.
ADSL2 + as a requirement for IPTV
With the data rates that can be achieved via ADSL2 +, several HD / SD IPTV channels can be transmitted at the same time, with sufficient data rate reserves for Internet surfing and VoIP , which is a prerequisite for commercial IPTV marketing. In addition to vendors such as Telefónica Germany (formerly HanseNet ), the ADSL2 + were planning their IPTV service from the beginning about which offers German Telekom since late summer 2007 after a parallel in 750 cities Streaming -enabled IP - Concentration Power has built its originally Telekom Entertain also offers Triple Play / IPTV projected for VDSL2 via ADSL2 +.
Interface variants
The end devices ( Customer Premises Equipment , CPE) and the remote stations in the central office , the DSLAM must be specifically designed to be able to work in the telecommunications network. In Germany only the ADSL-over-ISDN variant is used. Products that are intended for other regions therefore only work poorly or not at all in networks in other countries. For example, ADSL2 terminals for the Netherlands can usually not be used in Germany, since the "ADSL over POTS " variant is predominantly used here .
The individual variants are defined in the annexes of ITU-T G.992.3
| Annex | Designation in ITU-T G.992.3 | description |
|---|---|---|
| A. | Specific requirements for an ADSL system operating in the frequency band above POTS | ADSL2 over POTS |
| B. | Specific requirements for an ADSL system operating in the frequency band above ISDN as defined in ITU-T Rec. G.961 Appendices I and II | ADSL2 over ISDN |
| J | All digital mode ADSL with improved spectral compatibility with ADSL over ISDN | |
| L. | Specific requirements for a Reach Extended ADSL2 (READSL2) system operating in the frequency band above POTS | Version for increased range up to 7 km |
| M. | Specific requirements for an ADSL system with extended upstream bandwidth, operating in the frequency band above POTS | Increased upload speed up to 3.3 Mbit / s (at the expense of the download rate). |
See also
- For an overview of the standards, see the article on ADSL standards
Web links
- ITU-T Recommendation G.992.3: Asymmetric Digital Subscriber Line transceivers 2 (ADSL2)
- ITU-T Recommendation G.992.4: Splitterless asymmetric digital subscriber line transceivers 2 (splitterless ADSL2)
- ITU-T Recommendation G.992.5: Asymmetric Digital Subscriber Line (ADSL) transceivers - Extended bandwidth ADSL2 (ADSL2 +)
- Holger Skurk: ADSL2 +: The fast DSL successor . tecchannel.de, November 16, 2005.
- Axel Kossel: Breiterband. - Fast Internet access with ADSL2 + ( Memento from September 2, 2006 in the Internet Archive ). In: c't 11/06, p. 86.
Individual evidence
- ↑ Axel Kossel: Breiterband. - Fast Internet access with ADSL2 + ( Memento from September 2, 2006 in the Internet Archive ). In: c't 11/06, p. 86.
- ↑ IPTV-ADSL2 + expansion list from Telekom (Flash content) ( Memento of the original from September 27, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ ITU-T G.992.3: Series G: Transmission Systems and Media, Digital Systems and Networks - Digital sections and digital line system - Access networks - Asymmetric digital subscriber line transceivers2 (ADSL2); ITU-T Rec. G.992.3 (01/2005)
