What is the relationship between Tata Teleservices and Mumbai in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

The regulator further said that only Bharti Airtel in Mumbai and Tata Teleservices in Delhi met the laid-down quality of service (QoS) benchmarks for call drop rate, which as per norms should be less than 2%.

Answer: headquarters_location