The fall-back profile, with the maximum speed of 7,5 Mbps down and 0,5 Mbps up, is a profile applied to a VDSL2 line in case the latter is equipped with a modem that is not officially certified for the national DSL network in Belgium, or runs on a non-certified firmware version.
Why are there all of a sudden some hardware constraints?
The necessity of the fall-back profile has been raised together with a vectoring roll-out in Belgium and is caused by the nature of the vectoring itself. This technology is implemented at street cabinet (ROP) level where different copper lines arrive, all bundled in one cable. These lines disturb each other because they create cross-talk, which results in a loss of quality and a loss of performance (read: speed). In order to cancel the cross-talk between all VDSL2 lines in the bundle, there has to be a mechanism to obtain the cross-talk coefficients and to constantly—and in real time—calculate and update the anti-signals across hundreds of VDSL2 lines.
A non-certified modem, if installed on any VDSL2 line, will interfere with the calculation of the cross-talk between the lines. Thus, the cross-talk from some line will remain uncancelled, resulting in an unpredictable negative impact on all other lines of the bundle. In order to prevent it, all such devices will synchronize on a fall-back profile that will not create more cross-talk than the one coming from ADSL2+ lines and will not disturb the continuous cross-talk estimation.
How can I get my line out of the fall-back profile?
One of certified modems should be installed, provided that it is equipped with the appropriate firmware version. From the moment these requirements are fulfilled, TBF will be able to re-apply a provisioning profile.