g fastWhile VDSL2 and vectoring have already been launched as a service, the technology G.fast can get even more bandwidth out of copper cables. However, this new technology which was introduced at the end of last year by ITU, also has its drawbacks.

Along with the two standards G.9700 and G9701, ITU has approved a further bridge technology for the “last mile”. This technology is expected to offer the end customers high-speed data via copper cables which has been so far only possible via fiber optic connection. Like VDSL2 and vectoring before, G.fast enhaces again the possible bandwidth based on copper cables, however, only on very short distances in a satisfactory manner.

G.fast derives from the Recommendation ITU-T G.fast-psd and stands for “Fast access to subscriber terminals (FAST) – Power spectral density specification”. Currently, this technology is expected to provide the end user with bandwidths of up to one Gigabit per second. Up and downstream, of course, have to share bandwidth.

Susceptibility and coexistence with DSL

G.fast uses also higher frequencies than other previous standards. While VDSL bandwidth is up to 30 MHz, G.fast has initially a bandwidth of 106 MHz – the doubling to 212 MHz is already planned. However, high frequencies also may cause issues concerning susceptibility and coexistence with already existing xDSL connections.

Operating VDSL2 and G.fast in the same broadband bundle simultaneously is comparatively easy. In order to avoid a crosstalk during the transmission of both standards, G fast has to use higher frequencies than VDSL2. In addition to the start frequencies of 2.2 MHz and 8.5 MHz, ITU defines therefore also the entry points of 17,664 MHz and 30 MHz.

Dampening effects limit valuable bandwidth

Apart from crosstalk, G.fast struggles with dampening effects which limit the length of cables. According to ITU, only lengths below 100 meters allow data rates between 500 and 1,000 Mbit/s. 150 Mbit/s still remain with a lenght of 250 meters. Thus, this technology is suitable as an addition to FTTP and FTTdp (Fibre to the Building/distribution point) networks.

Series production not yet predictable

It will take some more time until G.fast will be put into practice. So far none of the large carriers has concrete plans concerning the introduction of this technology. However, the constantly increasing demand for bandwidth makes this technology a very promising and interesting topic and will continue to draw our attention in the future.

As an innovative manufacturer of network routers Teldat of course is engaged with this subject and is looking forward to the future developments.


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Michael Bindner

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