Osrūshana (Persian: اسروشنه) or Oshrūsana (Persian اُشروسنه - Ošrūsana), also known as Istarawshan (at present) Sudujshana, Usrushana, Ustrushana, Eastern Cao, 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.
The rulers of the Oshrusana or Ustrushana (Istarawshan) went by the title of "Afshin", and the most famous of whom was Khedār (Arabicised Haydar) b. Kāvūs. Our early knowledge of the ruling family of Oshrusana is derived from the accounts by the Islamic historians (Tabari, Baladhuri, and Ya'qubi) of the final subjugation of that region by the 'Abbasid caliphs and the submission of its rulers to Islam.
During the time when the first Arab invasion of the country took place under Qutayba b. Muslim (94-5/712-14), Ushrusana was inhabited by an Iranian population, ruled by its own princes who bore the traditional title of Akhshid or Afshin. The first invasion by the Arabs did not result in them controlling the area.
According to the Encyclopedia of Islam:
In 119 AH/737 AD the Turkic enemies of the governor Asad b. Abdallāh al-Ghasrī fell back on Usrūshana (al-Tabarī, ii, 1613). Nasr b. Sayyār subdued the country incompletely in 121/739 (al-Balādhurī, 429; al-Tabarī, ii, 1694), and the Afshin again made a nominal submission to Mahdī (al-Yaqūbī, Tarīkh , ii, 479).
Under Mamūn, the country had to be conquered again and a new expedition was necessary in 207/822. On this last occasion, the Muslim army was guided by Haydar (Khedar), the son of the Afshīn Kāwūs, who on account of dynastic troubles had sought refuge in Baghdād. This time the submission was complete; Kāwūs abdicated and Haydar succeeded him, later to become one of the great nobles of the court of Baghdād under al-Mutasim, where he was known as al-Afshīn. His dynasty continued to reign until 280/893 (coin of the last ruler Sayr b. Abdallāh of 279  in the Hermitage in St. Petersburg); after this date, the country became a province of the Sāmānids and ceased to have an independent existence, while the Iranian element was eventually almost entirely replaced by the Turkic.
However, during the reign of the caliph al-Mahdi (775-85) the Afshin of Oshrusana is mentioned among several Iranian and Turkic rulers of Transoxania and the Central Asian steppes who submitted nominally to him. But it was not until Harun al-Rashid's reign in 794-95 that Fadl ibn Yahya of the Barmakids led an expedition into Transoxania and received the submission of the ruling Akin, this Kharākana had never previously humbled himself before any other potentate. Further expeditions were nevertheless sent to Oshrusana by Ma'mūn when he was governor in Marv and after he had become Caliph. Afshin Kavus, son of the Afshin Karākana who had submitted to Fadl ibn Yahya, withdrew his allegiance from the Arabs; but shortly after Ma'mun arrived in Baghdad from the east (817-18 or 819-20), a power struggle and dissensions broke out among the reigning family of Oshrusana.
Kawus' son Khaydar, known by his royal title of Afshin, became a general in the Abbasid army and fought against Khurramite rebels and their leader Babak Khoramdin in Azerbaijan (816-837). In 841 Afshin was arrested in Samarra on suspicion of plotting against the Caliphate. A single location was used for the crucifixion of Afshin, Maziyar, and Babak's corpses. After his death Ustrushana was Islamified wheareas before he preserved temples from ruin.