\begin{equation}
    \label{eq3}
    \begin{split}
    \textrm{OR = } 
    \frac{\textrm{\emph{T} transmitted messages}-\textrm{\emph{N} delivered messages}}{\textrm{\emph{N} delivered messages}}, \text{if } N\geq 1 
    \\ \emph{cannot be defined}, \text{if } N = 0
    \end{split}
\end{equation}
