Proportionally fair allocation on a linear flow network ($x_0=1/N,x_i=M/(N{n}_i)$)

On unit-capacity links $1,\dots ,I$, route zero uses every link and route $i$ uses only link $i$. Let $N={\sum }_{r=0}^I{n}_r$ and $M={\sum }_{i=1}^I{n}_i$. Under proportional fairness, every active local route has $n_0{x}_0+n_i{x}_i=1$. Maximizing $n_0\log w_0+M\log (1-w_0)$ for $w_0=n_0{x}_0$ gives $w_0=n_0/N$ and the displayed per-flow rates on active routes. At the empty state departures vanish, and rates of absent flows may be set to zero.