What is "osrushana"

Osrūshana or Oshrūsana ( Persian اُشروسنه - Ošrūsana), also known as Istarawshan (at present) Sudujshana, Usrushana, Ustrushana, Eastern Chao, was a former Iranian region in Transoxiana. The Oshrusana lay to the south of the great, southernmost bend of the Syr Darya and extended roughly from Samarkand to Khujand. The capital city of Oshrusana was Banjikat. The exact form of the Iranian name Osrušana is not clear from the sources, but the forms given in Hudud al-'alam, indicate an original *Sorušna.