> 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/mtp2/signal-unit-error-rate-threshold.md).

# Signal Unit Error Rate Threshold

The MTP2 layer is responsible for retransmitting missing MSUs to the remote peer to ensure a valid flow of data. However, when the error rate of MSUs (the number of errored MSUs per unit of time) crosses a defined threshold, the link is taken out of service automatically (usually by the upper MTP3 layer).

The **Signal unit error rate threshold** parameter defines this threshold estimate to be monitored by the MTP2 layer before declaring the link as down.


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