The Cisco 12000 series four-port ATM line card complements the existing suite of ATM line cards for the Cisco 12000 series router product line, providing increased port density while delivering high-performance packet forwarding. The primary use of this card is for backbone applications. The new line card performs the segmentation and reassembly (SAR) of IP packets in accordance with RFC 1483, Multiprotocol Encapsulation over ATM Adaptation Layer 5 (AAL5).