Traffic Engineering in Segment Routing Networks Using MILP

In segment routing, a packet is forwarded along a path identified by a segment list. A segment list consists of segment identifiers (SIDs). A node-SID identifies a shortest-path segment, and an adjacency-SID identifies a link segment. A K-segment path is a path with no more than K segments. In this paper, we study the problem of finding a set of K-segment paths to carry all the flows in a given traffic matrix such that the maximum link utilization in the network is minimized. We first show that the solutions found by K-LP, an existing linear programming (LP) approach, are not optimal because K-LP does not support adjacency-SIDs. Focusing on 2-segment paths, a new LP formulation, denoted by e2-LP, is designed to support adjacency-SIDs in part. To fully support adjacency-SIDs, a mixed integer linear programming (MILP), denoted by K-MILP, is designed. Since solving K-MILP is time-consuming, a simplified version (K-sMILP) is also proposed. Finally, K-sMILP is extended to prevent excessive flow splitting or using paths that are too long.