For client mapping, the core can perform constant bit-rate (CBR) async mapping using GMP or packet mapping using GFP. With packet mapping, a bandwidth buffer is used for bandwidth management between the GFP mapper and the packet clients. The 10/25/40G CBR or packet clients are first mapped into LO ODU2, LO ODUFLEX or LO ODU3 via GMP or GFP-F and then multiplexed into ODTUmux and then to HO OPU4. The 100G client will map directly onto HO OPU4 via GMP.

The OTU4 core of Callisto supports 3 levels of OH insertions and extractions : register programming, memory programming and external programming via a dedicated OH port. The gFEC function can be disabled (or removed to save area) and a custom high-gain FEC can be used. The OTU4 core supports full alarm and OH inserts and extracts as specified in ITU G.709 and ITU G.798.