$1.$ Suppose all nodes are implementing Carrier Sense Multiple Access $($CSMA$),$ with collision detection $($CSMA$/$CD$).$ Suppose that the time from when a message transmission begins until it is beginning to be received at other nodes is $0\mathrm{.}4$ time units, and assume that a node can stop transmission instantaneously when a message collision is detected. $($Thus if a node begins transmitting a message at t$=2\mathrm{.}0$ and transmits that message until t$=3\mathrm{.}0,$ then any node performing carrier sensing in the interval $[2\mathrm{.}4,3\mathrm{.}4]$ will sense the channel busy.$)$ For each message, indicate the time at which each message transmission begins, or indicate that message transmission does not begin due to a channel that is sensed busy when that message arrives. Separate each value with a comma and no spaces, and if the channel is sensed busy, substitute it with $\text{'}$s