How Hexaly efficiently solves network design problems for Bouygues Telecom


Bouygues Telecom is a French mobile phone, Internet service provider, and IPTV company ($7.3 billion in annual revenue, 5,500 employees). For many years, Bouygues Telecom has used the expertise of Hexaly to develop custom software solutions for revenue management, data analysis, marketing operation planning, and network design.

Bouygues Telecom’s network design problem

The network of an Internet Service Provider is constantly evolving for robustness reasons: to reach new customers, to update old technologies, or to satisfy unique needs. In 2014, Bouygues Telecom’s strategy was to expand its core network to reach new customers with a very competitive DSL offer. Bouygues Telecom had to decide which of the 14,000 connecting nodes in France to link to its core network. Adding a new node to its core network increases the company’s revenue but comes with a cost. One must connect each new node to the core network through a network of preinstalled dark fibers. The company makes savings if several nodes share a common path to the core network. Bouygues Telecom’s objective was to connect around 1,500 new nodes to its core network to maximize its profits (revenues of new nodes minus connection costs).


Due to the large scale of the problem, which involves more than 1 million variables, the mathematical model is challenging to solve. As in most network design problems, the connectivity constraints modeling is intricate and leads to several auxiliary expressions.

  • 1,400,000 variables
  • 120,000 binaries
  • 360,000 constraints

Once modeled, Hexaly delivers quality solutions to this problem in a few minutes of running time on a standard laptop, including input and output processing times. In addition, the solution quality is checked by solving a combinatorial relaxation of the problem showing tighter lower bounds.

Bouygues Telecom’s network engineering team has been using Hexaly’s optimization solution since 2014. It enabled the company to connect 3,000 new nodes in addition to the ones they already operated. This strategy allowed Bouygues Telecom to offer a competitive DSL offer to a much larger customer base, contributing to gaining hundreds of thousands of new customers. Since then, Bouygues Telecom has leveraged several other optimization solutions built upon Hexaly to solve network design and expansion problems to deploy new telecom technologies.

Why Hexaly?

Bouygues Telecom’s network experts have to evaluate several scenarios with different economic hypotheses. In this context, having solutions in short running times is critical. Additional business constraints were subsequently added to the mathematical model to forbid impractical designs. Hexaly Optimizer handles these highly nonlinear design constraints straightforwardly, thus reducing the time between planning iterations.

Your services were a crucial help for our project. We have total confidence in Julien, who, over the years, continues to impress me with his work quality, versatility, and professionalism! True added value and innovative technology.

Alexis Bruno Network Software Architect, Bouygues Telecom

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