What is copper mixed fiber, still a point of reference in a large part of the country pending the extension of FTTH coverage.FTTH (Fiber-to-the-Home) is the "true fiber" because the fiber optic cable reaches the end user's router and does not stop, for example, at the street cabinet.We have seen the differences between FTTx and to what extent FTTH connections can offer significantly better performance due to the absence of the crosstalk issue and the practically negligible attenuation compared to copper.Suffice it to say that the signal attenuation detected on a copper link at a distance of 2-3 kilometers is the same as that which can be measured on a fiber link that is 150 kilometers long or more.In the case of mixed copper fiber connections FTTC (Fiber-to-the-Cabinet) the fiber cable reaches the cabinet in the street ("cabinet") while in the FTTE (Fiber-to-the-Exchange) scheme the copper section is even longer.In this case, in fact, the DSLAM devices are installed in the exchange, as was the case with ADSL, and not "delocalized" on the street in a position physically closer to the subscriber's real estate unit.FTTC and FTTE copper mixed fiber connections are marked in the pre-contractual phase and at the time of taking out a subscription with the yellow "FR" sticker.In the case of FTTH fiber offers, the sticker is green ("F").We are pushing more and more on the coverage of the country with FTTH technology: the 1 Giga Italy Plan provides that by 2026 all house numbers will be reached in FTTH where today we do not reach 300 Mbps, in gray and black areas or where already there is competition between telecommunications operators.The tenders for the adaptation of the network and the construction, where necessary, of new infrastructures were won by Open Fiber and FiberCop (TIM-Fastweb-KKR).The two companies, also in view of the potential creation of a single network, have already started a collaboration to speed up FTTH coverage of the white areas.This is confirmed by the AGCOM Communications Observatory (April 2022) which places copper mixed fiber at approximately 51% for the number of users who use it, while FTTH fiber stands at 13.3%.Still important values ​​(27%) for copper connections (in fact the old ADSL).FWA accesses wirelessly are worth about 8.5% of the market.Source: AGCOM, Communications Observatory, April 2022In the absence of FTTH coverage and waiting for it to be expanded, copper mixed fiber connections still allow data transfer speeds to be reached in some cases much higher than those obtainable with ADSL.This is possible thanks to the VDSL / VDSL2 (Very-high-bit-rate digital subscriber line) and EVDSL (Enhanced VDSL) technologies.Especially in the case of users more than 200 meters away from the street cabinet, the 17a profile is used: it theoretically allows to reach 100 Mbps in downstream and 50 in upstream.Commercially the connections came as 100/20 Mbps (with the second value referring to the upstream).In the case of long lines, the base profile 17a is used and sometimes the carrier is forced to lock with an SNR value of 9 dB or even 12 dB (usually a profile with SNR at 6 dB is used): this is to prevent the crosstalk and other interference present on the copper cable can lead to sudden disconnections.The use of a profile rather than another is easily ascertained by accessing the administration panel of the modem router and then going to the section containing the statistical line data.Using EVDSL with profile 35b it is even possible to reach up to 400 Mbps in downstream for users very close to the street cabinet.The telecommunications operators that offer the FTTC service make available up to 200 Mbps or in some cases 300 Mbps downstream.With VDSL / EVDSL the bandwidth literally collapses from 300-400 meters away from the street cabinet.This is why an old ADSL, in the case of long lines, could in some cases be even more stable than a mixed copper fiber scheme.To reduce the problems deriving from crosstalk or from interference caused by copper pairs close to the one being used, from mid-2020 AGCOM has opened the use of vectoring by operators.Vectoring is a technique that requires the involvement of the various operators but which allows to significantly reduce the problem of crosstalk.What is the limit of copper mixed fiber?We have presented a number of fiber speed considerations.In the Telecom Italia Group 2022 reference offer document there are a series of explicit references to the use of VDSL bonding to "squeeze" the potential of a copper mixed fiber connection to the maximum.VDSL bonding consists in the coupling (bundling, as TIM writes) of two FTTx connections (up to profile 35b) attested to the same ONU (Optical Network Unit, the apparatus installed on the street cabinet).Two twisted pairs terminated on a stud are brought to the customer's real estate unit.With this architecture it is possible to reach up to 400 Mbps downstream and 40 Mbps upstream;furthermore, the document explains that the most disadvantaged users who are connected to the UN with a long line could benefit significantly.It is not known whether VDSL bonding can be reconfirmed also for 2023: it is certain that the investments, also in view of a FiberCop-Open Fiber agreement that could arrive by the end of next October, are and will be more focused on extending coverage. 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