When a pair of quantum-entangled particles is separated, a change to one particle will affect the other instantaneously, wherever it lies in the universe. QECs exploit this effect to transmit binary data any distance. Two pairs of entangled particles are necessary for transmission and reception.
While QEC technology is extremely expensive and difficult to produce, it offers two enormous advantages. First, it allows instantaneous communication over any distance without reliance on the network of comm buoys, which is limited due to the sheer volume of space. Further, destruction of buoys hampers a foe's military intelligence; comm buoys are the first targets of raiders in wartime. Second, quantum communications cannot be intercepted between source and destination, allowing no "wiretaps."
Unfortunately, QECs cannot replace the galactic civil communications infrastructure. First, they have extremely limited bandwidth. A single entangled particle can only transmit a single qubit (quantum bit) of data at once. Second, the system's exclusively point-to-point nature precludes peer-to-peer networking and data dissemination through the galactic extranet.
The most strategically appropriate military application of QECs is at the headquarters level. Each Alliance colony would maintain a QEC at its military headquarters and each fleet flagship in its CIC. All the pairs for these would be located at a central facility within Arcturus Station. During an attack, a facility would signal Arcturus to transmit its information to every other fleet and colony. However, destruction of the comm center at Arcturus would collapse the entire network.