[Wdll]

****ty attitude aside, I am not sure what you are asking exactly.
A unit with a radio can have contact with its superior with its radio or if the superior is close enough, by shouting/etc.
When said unit you press the R for Rally, then when the unit try to contact its superior will do so and hopefully get some help. To get help it needs the contact I mentioned. There are two ways that it won't get Rally help from superior. One, if the unit is out of contact. Two, if it is in radio contact but when you try to ask for help (pressing R) there is an interruption (which is not shown as specific message of failed communication but as a fail at rallying or even while you see your unit is in contact with its superior, you still don't get any help because of said failure).

Even if there is contact 100% working, the rally can still fail. Such is life.