airFiber - Is auto modulation a hitless protocol?

Yes, airFiber Adaptive Modulation is hitless. airFiber uses a selective acknowledgement based protocol to ensure that no packets are lost as a result of link adjustements such as changes in modulation. The only thing you should see during a transistion is a short spike in latency while the rates change.

Make sure Flow Control is enabled to avoid any potential Rx buffer overflow when link is heavily loaded. 

Important note: if the link needs to modulate down it will be capable of carrying less traffic and thus may lose packets as a result of overflow (i.e. the user rate is 700 Mbits and the link negotiated to 500 Mbits).