Draw arc between points and label

Question

As shown in the attached picture, I wish to draw that red arc between the left node and the right node and label it as ABC (shown in attached image).

How can I do it? The code that I have worked out till now is given as follows:

 \begin{tikzpicture} 
 \begin{scope}[minimum width=15mm,minimum height=10mm]
 \node[draw,line width=0.25mm,rounded corners, label= 
 {[align=center]above:ABCD\\ abcdefgh 123 \\mnopqr}] (v1) at (0,0) {$G_F(s)$};
 \node[draw,line width=0.25mm,rounded corners, label= 
{[align=center]above:mnomno \\ xyzxyzxyz}] (v2) at ($(v1)+(10,0)$) {$R(s)$};
 \node[draw,line width=0.25mm,rounded corners, label={[align=center]below: \\ abcdef integer\\abcedef}] (v3) at ($(v1)+(5,-4)$) {$G_{I}(s)$};
  \end{scope}
  \draw[->] (v1) -- (v2) node[pos=0.5,sloped,above]{ABCDEF 
approach}node[pos=0.5,sloped,below]{\textcolor{red}{\textbf{Proposed 
approach}}};
      \draw[->] (v1) -- (v3) node[pos=0.5,sloped,above]{Approach 1}; ;
  \draw[->] (v3) -- (v2)node[pos=0.5,sloped,above]{Approach 2};
 \end{tikzpicture}

Answer 1

You can specify a /tikz/to path style and do something like \draw (v1) to[my style] (v2) or a simpler solution:

\documentclass[border = 5pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}


\begin{document}
\begin{tikzpicture}
  \begin{scope}[minimum width=15mm,minimum height=10mm]
 \node[draw,line width=0.25mm,rounded corners, label=
 {[align=center]above:ABCD\\ abcdefgh 123 \\mnopqr}] (v1) at (0,0) {$G_F(s)$};
 \node[draw,line width=0.25mm,rounded corners, label=
{[align=center]above:mnomno \\ xyzxyzxyz}] (v2) at ($(v1)+(10,0)$) {$R(s)$};
 \node[draw,line width=0.25mm,rounded corners, label={[align=center]below: \\ abcdef integer\\abcedef}] (v3) at ($(v1)+(5,-4)$) {$G_{I}(s)$};
  \end{scope}
  \draw[->] (v1) -- (v2) node[pos=0.5,sloped,above]{ABCDEF
approach}node[pos=0.5,sloped,below]{\textcolor{red}{\textbf{Proposed
approach}}};
      \draw[->] (v1) -- (v3) node[pos=0.5,sloped,above]{Approach 1}; ;
  \draw[->] (v3) -- (v2)node[pos=0.5,sloped,above]{Approach 2};

  %% new line
  \draw[red] (v1) .. controls ($(v1)+(1,-8)$) and ($(v2)+(-1,-8)$) .. (v2) node[midway, below]{PCB};
\end{tikzpicture}
\end{document}