Ketuvot 94b: Rav Nahman was a Dayan, and Rav Sheshet was not:
Rashi's explanation: I am a Dayan:according to the Rosh HaGola and the
Yeshiva! So Rav Shesheth was not appointed by the Rosh Hagola - was his authority not recognized by his own Yeshiva? Why go by the Yeshiva of Naharda'a?
Perhaps: Rav Sheshet was a disciple of Rav Huna in Sura - and Rav Nahman was
quite serious about the relative authority of the Yeshivot, as we remember
from his relationship with Rav Huna - according to Rav Reuven Margoliot!
Does this seem farfetched?
Yeshayahu HaKohen Hollander
The term "Yeshivah" refers to the Yeshivah in Eretz Yisrael and not in Bavel, and refers to one who received Semichah from his rebbi, who received it from his rebbi, and so on until the Yeshivah in Eretz Yisrael (as the Gemara in Sanhedrin 5a says regarding Rabah bar Rav Huna).