Modular Interface Cards (MICs) install into two slots in the front of the ACX4000 router and provide the physical connections to various network media types. The slots are labeled1/0 and1/1. MICs receive in coming packets from the network and transmit outgoing packets to the network. During this process, each MIC performs framing and high-speed signaling for its media type. Before transmitting outgoing data packets through the MIC interfaces, the packet forwarding engine encapsulates the packets received.