Incremental Versus Optimized Network Design

TL;DR

This paper compares incremental network design to traditional optimized design, analyzing cost, topology, delay, and robustness, and finds incremental design is cost-effective for small expansions and maintains stability over time.

Contribution

It formulates and evaluates incremental network design approaches, highlighting their advantages and limitations compared to optimized design in practical network evolution.

Findings

Incremental design incurs some cost overhead but remains stable as networks grow.

Evolving existing networks is less costly than designing from scratch for small expansions.

Incremental design maintains topological similarity and robustness over time.

Abstract

Even though the problem of network topology design is often studied as a "clean-slate" optimization, in practice most service-provider and enterprise networks are designed incrementally over time. This evolutionary process is driven by changes in the underlying parameters and constraints (the "environment") and it aims to minimize the modification cost after each change in the environment. In this paper, we first formulate the incremental design approach (in three variations), and compare that with the more traditional optimized design approach in which the objective is to minimize the total network cost. We evaluate the cost overhead and evolvability of incremental design under two network expansion models (random and gradual), comparing incremental and optimized networks in terms of cost, topological similarity, delay and robustness. We find that even though incremental design has some cost overhead, that overhead does not increase as the network grows. Also, it is less costly to evolve an existing network than to design it "from scratch" as long as the network expansion factor is less than a critical value.