Complex sentence: In practical scenarios, a T.38 fax call has at least part of the call being carried over PSTN, although this is not required by the T.38 definition, and two T.38 devices can send faxes to each other.
Split into simpler sentences: In practical scenarios, a T.38 fax call has at least part of the call being carried over PSTN. Although this is not required by the T.38 definition, and two T.38 devices can send faxes to each other.