The Cisco 12000 SIP-50 provides a common 10Gbps forwarding and queuing engine responsible for packet classification, forwarding, queuing, and accounting without compromising performance. The Cisco 12000 SIP-501 has two forwarding engines, one for ingress and one for egress. This allows the user to implement different features and QoS policies for the ingress and egress interfaces. The multicast replication is done by the egress forwarding engine, hence a very scalable multicast with built-in QoS.