Bridge diode works as transient voltage clamp to protect data lines. Here’s Vishay’s app note, link here (PDF)
Local Area Network (LAN) data lines require protection against direct and induced transient over voltages on the lines. Protecting these lines and the associated network is not a trivial task. The power range is somewhere between static discharge (very low power) and lightening protection which is at the other end of the spectrum (high power).
Power handling capability is only one aspect of the design. The designer must take care not to “load down” the line with a highly capacitive TVS or R/C network. As data rates go beyond 50 mb. It is not possible to use a TVS unit with capacitance above 100 pF to 200 pF. Most standard TVS devices have zero volt capacitance values greater that 500 pF. To make matters worse, the lower voltage TVS units have higher capacitance values than their higher voltage counterparts.
Read more Here