A: Can you hear me?
B: Yes
A: What time is it?
B: 5 o'clock
A: Thank you, goodbye!
B: Goobye!
Nothing is lost compared to:
A: Can you hear me?
B: Yes
A: Yes
A: What time is it?
[...]
A: Can you hear me? B: Yes B: What time is it? A: ...
At the point that B has replied Yes, B knows that it can hear A and that it can send to A but it doesn't know that A can hear B. As long as A makes the first move in the rest of the conversation that's fine - the next message from A confirms that B's "Yes" was received, but if A has nothing to say then B has to send it's next query and hope that A received the Yes successfully. If it didn't then B thinks the connection is established but it actually hasn't been.
That conversation can also go like;
A: Can you hear me?
B: Yes
A: What is the full unabridged story of War and Peace?
B: <...>
A: I am going to a take a nap for now, goodbye!
B: ... Goodbye!
Both sides need to know to "commit" to the connection.
A: If you can hear me, what time is it?
B: Yeah I can hear you; it’s 5.