The QSFP-DD Series offers up to 400Gbps transmission speeds and features 1-by cages. 4 Tbps aggregate bandwidth in a single switch slot. This guide provides a comprehensive overview of QSFP-DD compatible switches across major vendors, explains the fundamentals of backward compatibility at the port level, and outlines how to verify transceiver compatibility before procurement. The S9855 can be used in the core and aggregation. Amphenol's QSFP-DD high-speed connector family features a scalable, high-performance interconnect platform with 76 contacts on a 0. 8mm pitch and a dual-mating interface.