the whole transmission is complete [*provided that*]{} he does not perform any measurement at this moment. For instance, having received $r l_{\rm
min}$ qubits in the message tape from Alice, Bob is sure that at least $s=\lfloor r l_{\rm min}/ l_{\rm max} \rfloor$ signals have already arrived. He can separate those $s$ signals immediately using the length information of each signal. This part of the decoding process is rather straightforward and we will skip its description here.

The important observation is, however, the following: If Bob were to perform a measurement on his signals now, he would find that they are of poor fidelity. The reason behind this has already been noted in Section 2. Even though the subsequent encoding process does not involve Bob’s system, there is still entanglement between Alice and Bob’s systems. More specifically, the shifting operations in the remaining encoding process by Alice require explicitly the information on the total length of decoded signals. Before Bob performs any measurement on his signals, it is, therefore, crucial for Alice to disentangle her system first, as mentioned above.

Suppose in the middle of their communication in which Bob has already received $K \bar{L}$ qubits from Alice, Bob suddenly 