H31-321-ENU exam is required by Huawei HCNP-MSTP Transmission certification. HCNP-MSTP Transmission exam covers OptiX SDH equipment commissioning, complex networking of OptiX SDH equipment, board replacement of OptiX SDH equipment, discrete service analysis and handling, tests for common Ethernet service indicators, clock protection of OptiX OSN equipment, SDH equipment interconnection, ECC maintenance, pointer justification, routine maintenance