The MTP1 layer is the physical SS7 layer and is responsible for the HDLC framing of SS7 packets (usually called MSU – Message signaling unit). Besides the transmission and reception of frames and the calculation of CRC, this layer is also responsible for monitoring and reporting the quality of the link based on the number of failures detected (CRC errors, unexpected packets). Using specially formatted packets (LSSU and FISU), this layer ensures that the communication with the peer side is always valid and synchronized, even when the communication link is supposedly idle (no MSU being sent).
TelcoBridges and MTP1
TelcoBridges supports MTP1 as part of its SS7 signaling stack.