What MAC protocol is slotted aloha an example of?

I've had some discussion on Twitter recently about whether this is a good example of MAC protocol slotted aloha.

(MAC protocol slotted aloha is a way to deal with collisions in a shared medium.) This is the kind of thing that comes up when you have so many people in so many different locations doing stuff simultaneously that they all start dropping their packets at the same time, one by one. How does one go about making sure that your packet gets through, can we please come up with a name for this? why isn't it called X-ing? etc. I agree with Scott in that slotted aloha is useful but perhaps not the most appropriate choice of name, and also that the MAC protocol in question isn't in fact slotted aloha. At the same time, the protocol might better characterized as slotted aloha with acknowledgements and retransmissions or slotted aloha with a retransmission interval. You may say that they are equivalent. I say that they are more or less. As a way to explain them, here is a picture that shows the relevant parts of a MAC protocol in action, including the concept of how collisions are resolved.

The diagram of the network is in fact a little misleading because it isn't the case that there is a shared medium where a single stream is taking over. Instead, the multiple clients are each sending their own packets in a separate transmission window. The shared medium here is just the channel that connects these two clients and provides a link for transmission. The MAC protocol here is slotted aloha, and it can be more clearly seen in this more explicit form:

Client A sends Packet 1. Client B ACKs Packet 1. Client A retransmits Packet 1. Client B ACKs Packet 1 again.

The first thing to notice is that the time of delivery is very much dependent on who is receiving at what time. What happens when Client B receives the first part of Packet 1 at time t=0? In that case, it will send its ACK (ACKnowledge) back to Client A at time t=1. The two transmissions will overlap and there will be a collision, meaning that one or both packets will get lost.