How Mellanox is able to increase his speed of the interconnect.
how from 56 to 100 GBps
Need technical document for understanding.
Not sure exactly what you're asking here so I'll answer in terms of the IBA spec.
56 Gbps is 4x FDR. 100 Gbps is 4x EDR. A port can support FDR, EDR, or both. When peer ports negotiate the link between them, the link should come up at the maximum speed/width shared by the peer ports if there are no difficulties with the link negotiation. If some issue occurs (perhaps cable only works at FDR for some reason), a downgraded speed or width is possible.