  The generalized amplitude damping channel (GADC) is considered an important
model for quantum communications, especially over optical networks. We make two
salient contributions in this paper apropos of this channel. First, we consider
a symmetric GAD channel characterized by the parameter $n=1/2,$ and derive its
exact classical capacity, by constructing a specific induced classical channel.
We show that the Holevo quantity for the GAD channel equals the Shannon
capacity of the induced binary symmetric channel, establishing at once the
capacity result and that the GAD channel capacity can be achieved without the
use of entanglement at the encoder or joint measurements at the decoder.
Second, motivated by the inevitable buffering of qubits in quantum networks, we
consider a generalized amplitude damping \emph{queue-channel} -- that is, a
setting where qubits suffer a waiting time dependent GAD noise as they wait in
a buffer to be transmitted. This GAD queue channel is characterized by
non-i.i.d. noise due to correlated waiting times of consecutive qubits. We
exploit a conditional independence property in conjunction with additivity of
the channel model, to obtain a capacity expression for the GAD queue channel in
terms of the stationary waiting time in the queue. Our results provide useful
insights towards designing practical quantum communication networks, and
highlight the need to explicitly model the impact of buffering.
