ers. Since there are no customer inter- faces on this equipment, there is no data plane traffic at all. There was typically only a pair of redundant, low-speed interfaces to connect the RRs to core routers for the purposes of exchanging the routing state. Today, the RR function can be deployed as a VNF running on the AIC cloud. In addition to a tremendous reduction in unit cost, there is also dramatic improvement in performance since the servers in the AIC infrastructure are much more state-of-the-art than the control processor that was embedded in RRs based on routers. 13.3 SDN CONTROL OF THE PACKET/OPTICAL CORE As discussed, the performance of the packet core has improved considerably with the implementa- tion of TE using the RSVP protocol. The bandwidth-aware nature of this protocol allows traffic flows to be moved around the network to find available capacity and avoid congestion. However, eventually there are limitations because these protocols are distributed. The head-end node for each tunnel is independently calculating routes. Often these requests collide, and several tunnels will need to retry to find a path meeting the bandwidth needs. As the network gets more congested, these retries occur more frequently and it takes a longer time to converge. The way to improve performance (i.e., faster convergence) and to eliminate congestion is to move to a centralized approach using SDN control. An SDN system has visibility to data from the entire network to form a global view of demand and capacity, and with efficient algorithms, it can better optimize latency and congestion. An added advantage is that this can lead to higher utilization of the network, since extra capacity to handle these congestion cases will not be needed. 13.3.1 CENTRALIZED TE The core packet network uses distributed RSVP-TE signaling to respond to traffic changes, fail- ures, etc. Distributed protocols have been hardened over many years of operation, and perform extremely reliably in the network. But as discussed above, they do not always f