Telecom infrastructure company Zayo revealed it was selected by an unnamed major US wireless operator to provide fibre for new macro towers in 21 states.

Zayo said the agreement, its largest mobile infrastructure contract to date, includes the deployment of dark fibre across 30 markets. In addition to using existing assets, Zayo noted it will construct hundreds of route miles of new fibre to meet the operator’s needs.

The deal supplements an earlier contract between Zayo and the unknown operator from September 2016 which included the deployment of dark fibre to 1,800 cell sites in 26 markets. Across both contracts, Zayo said it will connect “thousands” of macro towers for the customer.

While Zayo did not name its partner or specify what markets it would be working in, it said the agreement comes as the operator aims to improve coverage and capacity across its network to keep up with traffic demands and prepare for 5G deployments.

All four tier-one US operators are working to densify and strengthen their networks ahead of 5G, meaning there are a few likely candidates for Zayo’s partner.

In June 2017, T-Mobile US’ VP of Radio Network Technology and Strategy Karri Kuoppamaki announced the operator had decided to use dark fibre partners to provide backhaul for its small cell densification project.

But Sprint’s publicly stated plans are perhaps the best match for Zayo’s announcement. In December 2017, the operator unveiled an investment roadmap which included the construction of “a few thousand” new towers as part of an effort to improve service in specific markets at the fringe of its existing footprint.