The Cisco 6400 supports three half-height and one full-height node line card (NLC) modules. The OC-3/STM-1 MM NLC has two 155-Mbps Synchronous Optical Network (SONET) Synchronous Transport Signal level 3, concatenated/Synchronous Digital Hierarchy (STS-3c/SDH) ports for multimode fiber connections used as uplink and downlink interfaces.