> For the complete documentation index, see [llms.txt](https://tmediadocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://tmediadocs.telcobridges.com/telecom-references/ss7-and-signalling/ss7/mtp1-layer.md).

# MTP1 Layer

The MTP1 layer is the physical SS7 layer and is responsible for the [HDLC](/telecom-references/transmission-and-lines/hdlc.md) framing of [SS7](/telecom-references/ss7-and-signalling/ss7.md) 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.


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