Should outside istance be allowed during a match?

No it shouldn't be allowed, but it has been going on for a long time & is an old trick of players trying to break the concentration of their opponent & unsettle them. McEnroe was an expert at it. He spent half the time arguing with umpires & linesmen just to upset his opponent. It should be stopped as it's very unsporting. As for line persons, many of them are too old for the job. It should be confined to people under 40 in my opinion.