This is essentially a phone call in a professional setting- I would treat it accordingly. If you are speaking to an international client and the connection is so bad that you cannot comfortably interact with the client, it is best to state clearly that the connection is bad and that you will call back immediately. If the connection is still of low quality after re-dialing, I would send an immediate email stating the problem and making it clear that you want to schedule another interview as soon as feasible.
A poor quality connection is not your fault- just make it clear that you made a genuine effort to contact the interviewer and that you are not trying to avoid the interview.