G.fast

G.fast is a newly emerging ITU- T standard of DSL technology and is a successor standard to VDSL2. The transmission technique is based as VDSL2 vectoring on vectoring. G.fast promises data transfer rates of up to 1 Gbit / s over existing copper cable telephony and is due to the high frequencies only for short cable distances up to 250 meters suitable.

General

Alcatel Lucent announced in mid-2013 announced that it has achieved under laboratory conditions 1.1 Gbit / s on a single, 70 m long copper wire pairs. At 100 m was still 800 Mbit / s. Since G.fast is very susceptible to crosstalk, must be used for an efficient use under real conditions vectoring to compensate for interference.

For transmission frequencies up to 212 MHz is used, but in contrast to the number of bits per VDSL2 subchannel (carrier) is limited to 12 ( for VDSL 15 bits). Due to the high frequencies and thus signal attenuation occurring G.fast is only applicable for short line distances up to 250 m. Therefore it is now believed that a mixed operation, together with other xDSL technologies such as VDSL2, envisaged in the future.

ITU wants G.fast standardized by the end of 2014. Permanently powered installations are expected around the end of 2015.

Application

At present ( 2013) is G.fast not yet commercially available. In Switzerland Swisscom since June 2012 G.fast -enabled Equipment operates but in a FTTdp - pilot in the individual regions. From the end of 2013, the hardware is being expanded in other parts of the country. Telekom Austria also testing a new technology in their network and reached in tests 500 Mbit / s over 100 m of copper cable as they were installed in the telephone network. In Germany, the German Telekom plans to test the technology in a field trial in the year 2014 and thus also up to 500 Mbit / s to realize over the nationally -developed copper cable network.

Technology

By the use of much higher frequencies than, for example, in the VDSL also takes the crosstalk to solid. By means of vectoring can be largely offset this though. But for new and better algorithms are needed. In addition, higher frequencies also mean more calculations per second for the vectoring calculations in the DSLAM. Its computing power must increase exponentially with an increasing number also DSL lines at the DSLAM.

Open Issues

Has not yet stable, operating mode, some problems to be solved. For this, the ITU- T has created a working group, which is concerned with.

G.fast used frequencies up to 212 MHz, which lie in the FM radio sector. The subscriber lines can act like long antennas. Thus, it is possible that the radio devices to be disturbed. The time is not yet known how this problem shall be solved.

As with vectoring, which is fundamentally important for the operation of G.fast, there are some challenging problems for the telecommunications company. So, for example, the CPE must support at the retail side of this standard and a DSLAM should serve all ports in the same cable bundle in the optimal case, that he has control of the crosstalk in the complete network.

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