Complex sentence: The data-rate of 20 Gbit/s is made possible by joining the two existing 10 Gbit/s-channels, which does not change the maximum bandwidth, but makes using it more flexible.
Split into simpler sentences: The data-rate of 20 Gbit/s is made possible by joining the two existing 10 Gbit/s-channels. This does not change the maximum bandwidth itself but makes using it more flexible.