MTP2
From TBwiki
The MTP2 layer in the SS7 protocol stack defines the functions and procedures of the signaling system for a reliable transfer of signaling messages over an SS7 signaling link. The MTP2 layer is a service provider to the MTP3 link layer, and at the same time it is a service user of the underlying trunk layer.
A conceptual illustration of the MTP2 layer is provided below:
