The PA-POS-OC3 interface provides a direct connection between the supported router or switch platform and external networks. You must use the appropriate optical fiber cables to connect the PA-POS-OC3 with an external OC-3 network.Packet data is transported using Point-to-Point Protocol (PPP) and is mapped into the STS-3c/STM-1 frame. The encapsulations used add approximately half the number of bytes of transport overhead as that involved with ATM using ATM Adaptation Layer 5 (AAL5) and line card control (LCC) Subnetwork Access Protocol (SNAP) encapsulations.