Consider three nodes $A,B,C$ connected in series. Node $A$ is connected to Node $B$ via $3 \text{ Gbps}$ link, $500 \text{ km}$ length. Node $B$ is connected to Node $C$ via $60 \text{ Mbps}$ link, $15 \text{ km}$ length. The links are full duplex, but no other traffic on the links. A large file is to be sent from Node $A$ to Node $C$. Packers are $1024$ bytes. Assume velocity of propagation as $2\times 10^8 \text{ m/sec}$. What is the round trip time? __________ $\text{msec}$