What are "Batei ha'Chatzerim"?
Rashi (citing Targum Onkelos) and Targum Yonasan: They are houses in open towns without walls (from the time of Yehoshu'a bin Nun
What is the meaning of "Al S'dei ha'Aretz Yechashev"?
Rashi: It means that they have the same Din as fields (of inheritance - Rashi in Kidushin Ibid.) - to be redeemed up to the Yovel, and to return to the owner when the Yovel arrives.
Targum Yonasan: It means that they have the same Din as tents that are spread out over the field. 1
Na'ar Yonasan: Hence the Torah writes "Al S'dei ha'Ha'Aretz" and not "ki'S'dei ha'Aretz"
What are the ramifications of "Ge'ulah Tih'yeh Lo"?
Rashi: It means that the seller may redeem the house immediately 1 if he so wishes.
Rashi: As opposed to a field, which he cannot redeem before two years.
Why do Batei ha'Chatzerim revert to the seller in the Yovel, even though houses is a walled town do not?
Ramban (29), Moshav Zekenim (29): Batei ha'Chatzerim are for people who work the fields. Consequently, they have the same law.
What are the implications of "uva'Yovel Yeitzei"?
Rashi: It implies that the house reverts immediately to the seller, without him having to compensate the purchaser. 1
Sifsei Chachamim (from Erchin 29b): This does not apply to a field sold a year before Yovel. Since a field is always sold for at least two years, the buyer gets another year after Yovel.