services model
A services model is an abstract tool for representing the interrelationships for communication between communication partners. It is a multi- layer model that provides services at specific network transitions.
An example of such a service is connection establishment. It occurs when a service user "A" wants to communicate with service user "B". "A" sends a request to the service provider for this purpose.
The service provider in turn informs "B" (indication) that "A" would like to communicate with it. "B" now sends a response, which can be positive or negative. In the case of a positive response, the service provider sends a confirmation to the service user "A" that the connection can be established.
This model is based on handshake operation and is referred to as two-way handshake.