Reliance Jio Infocomm, which aims to roll out a nationwide 4G network in India, has signed a tower-sharing agreement with Reliance Communications (RCom) worth INR120 billion ($2.1 billion) over 15 years.

Under the terms of the deal, Jio Infocomm will lease up to 45,000 ground and rooftop towers across RCom’s nationwide network. The two companies will also have joint working arrangements to configure the scope of additional towers to be built at new locations. This, they say, “will ensure deep penetration and seamless delivery of next generation services”.

The tower-sharing agreement is the latest sign of thawing relations between the Ambani brothers since they carved up their father’s Reliance business in 2005.

In April, the two companies signed an inter-city fibre-sharing agreement as part of a long-term business cooperation framework.

Mukesh Ambani, India’s richest man, controls Reliance Industries (of which Jio Infocomm is a part), while younger brother Anil Ambani controls RCom, which is struggling with debt.

According to India’s Economic Times, Jio Infocomm is still about a year away from 4G launch. The company bought pan-Indian spectrum in 2010 for roughly INR130 billion.