Warning - the following is a bit off topic for an aviation forum but it is relevant to this thread.
"The term "ping" doesn't refer to a particular mode of transmission but a particular type of transmission. That is, a ping refers to the content of the data packet. A ping is either some version of an ACK or a "keep alive" message.
Typically one node broadcasts a message to another node. The node receiving node either returns an ACK (acknowledgement) or a keep alive. Which it returns depends on design specifications. It is something said that when this roundtrip has been successfully completed it is called a "handshake". However, a handshake contains more data than ping because a handshake contains data regarding the network protocol"
A reasonable generalization but not really accurate. Protocols use very explicit language to define their operation (e.g. ISO 8208 CALL REQUEST, ISO 10747 KEEPALIVE). In this case the protocols are pre-determined and there are quite a few of them (AMSS, ISO 8208, IDRP, X.25, X.121)! These protocols are layered with one depending on another for proper operation.
It is important to understand the concept of layers in networking. Microsoft has a good link
here if you want to learn more about network layers in general.
This pdf published by Boeing (slide 12) shows an architectural diagram of ACARS. Blocks denote "layers" stacked upon one another. There are 3 stacks depicted ("Communications Management Unit", "Datalink Service Processor" and "User Ground System"). You can think of data flowing up and down each stack and horizontally between them. Note the dashed line connecting "Satellite Data Unit" (in the airplane) and "AMSS GES" (satellite ground station). The satellite itself is not shown but you could think of it as represented by the dashed line. This is where the "ping" is occurring.