In the book,
the aliens possessed a weapon called a dreadnought (if I remember correctly) that allowed them to interrupt human quantum communications when both sender and receiver were inside the dreadnought's range. The result of this was that the human defence drones were rendered useless once a dreadnought managed to get close to Earth after the base on the Moon (from where the drones were controlled) was destroyed.
which obviously raises the question
Why did the people from Earth not establish communication relay points in deep space, so that in the event of a dreadnought attack they could maintain communications via these relay points?
Was there a clue given in the story on why this idea was not considered?
Update: OK, based on phantom42's answer below, I want to clarify a few things:
Firstly, I'm not talking about classical (radio) communications at all.
According to the book (and affirmed by phantom42's quotes), quantum communication is possible inside the disrupter field as long as either the sender or receiver is outside of the field. Humans have access to spaceships (or drones) that can traverse the solar system in hours. Quantum communication is instant, so the distance between sender and receiver is not an issue.
So what stops the humans from sending a spaceship to Jupiter (or anywhere outside of the disrupter field) that contains two quantum communicators. Bob on earth establishes a communication link from earth to spaceship communicator 1. This is fine, because the spaceship (receiver) is outside of the disrupter field. The spaceship then relays any information it received from communicator 1 to communicator 2 - this can be done via classic means, because the spaceship is well outside of the disruptor field. Jane on earth then receives comms from communicator 2, which effectively allows Bob and Jane to talk to each other. Sort of like an SSH tunnel over space. :)