Alanic horseman

Could someone please tell me what is the most likely reconstruction of
the Alanic word for "horseman". Modern Ossetic has baræg and bæx-dzhyn
(lit. "one having a bæx" – a horse, that is). I'm not sure these are
inherited Iranian and not borrowed from some Caucasian language. But
if they are, what is the earlier form? I'd expect something with Ir.
aspa- (Oss. jæfs-) as the first element.

And if you can tell me what the Hunnish word was, I'll be enormously
grateful :)