1. Maintaining communications capabilities during major natural disasters and other emergency situations –final report;Study Group on Maintaining Communications Capabilities during Major Natural Disasters and Other Emergency Situations,2011
2. The mechanism of emergency and priority calls in the present network;NTT-East,2007
3. M. Nakano, M. Suzuki, M. Tanaka, Damage to Lifeline Systems, Their Recovery, and New Measures against Earthquake Disaster–Communication Facilities, Kansai Chapter of Japan Society of Civil Engineers, 1998, pp. 47–57. (in Japanese). URL https://www.jsce.or.jp/library/eq10/book/45943/6-0008.pdf.
4. Telecommunication Systems Division, Telecommunications Bureau, Survey on Communication Conditions Just After the Great East Japan Earthquake, Ministry of Internal Affairs and Communications. 2011 (in Japanese). URL http://warp.da.ndl.go.jp/info:ndljp/pid/10367640/www.soumu.go.jp/main_content/000136157.pdf.
5. NTT-East, Disaster emergency message. 1999. URL https://www.ntt-east.co.jp/en/saigai/voice171/.