enhancing the survivability. The network is more intelligent; it seeks out and finds available band- width. Higher utilization means the deployment of proportionally less restoration capacity trans- lating to lower unit cost. 13.2.3 SEGMENT ROUTING With RSVP-TE, a network with N nodes will need N*(N-1) tunnels. All nodes need to keep state information about all TE tunnels for which they are the head end, tail end, or mid-point. This drives up resource needs on the router. One emerging and promising technology that might help reduce the state that needs to be retained by nodes while supporting similar functions as RSVP-TE, is seg- ment routing. Segment routing provides a mechanism for source-based routing without requiring intermediate routers to maintain state information. The source router determines a path and encodes it in the packet header as an ordered list of segments [14]. The intermediate routers follow the instructions provided in the segments and forward the packet based on the segment. For MPLS forwarding, the segment will be represented by MPLS label and list of segments as MPLS label stack. The basic principles of segment routing are explained through a few examples below. 13.2.3.1 Packet Forwarding under Normal Conditions Consider a simple network shown in Figure 13.17. Each router assigns a prefix-segment for its loop- back address (e.g., 16006 for R6 router, etc.), which will be globally unique (similar to loopback address) and floods it via the core routing protocol. All routers in the network will learn the prefix- segment and will use this label to send the traffic to the destination router. There is no need for another protocol like LDP to advertise the labels. In the example below, if router R1 wants to send the packet to R6, it determines the shortest path is R1-R2-R3-R6 and will add label 16006 and send it R2. R2 will swap 16006 to 16006 and send it to R3, which will then forward the packet to R6. A flow is the exchange of data between a source and destination, It is important to keep the p