  The terminal backup problems (Anshelevich and Karagiozova (2011)) form a
class of network design problems: Given an undirected graph with a requirement
on terminals, the goal is to find a minimum cost subgraph satisfying the
connectivity requirement. The node-connectivity terminal backup problem
requires a terminal to connect other terminals with a number of node-disjoint
paths. This problem is not known whether is NP-hard or tractable. Fukunaga
(2016) gave a $4/3$-approximation algorithm based on LP-rounding scheme using a
general LP-solver. In this paper, we develop a combinatorial algorithm for the
relaxed LP to find a half-integral optimal solution in $O(m\log (nUA)\cdot
\operatorname{MF}(kn,m+k^2n))$ time, where $n$ is the number of nodes, $m$ is
the number of edges, $k$ is the number of terminals, $A$ is the maximum
edge-cost, $U$ is the maximum edge-capacity, and $\operatorname{MF}(n',m')$ is
the time complexity of a max-flow algorithm in a network with $n'$ nodes and
$m'$ edges. The algorithm implies that the $4/3$-approximation algorithm for
the node-connectivity terminal backup problem is also efficiently implemented.
For the design of algorithm, we explore a connection between the
node-connectivity terminal backup problem and a new type of a multiflow, called
a separately-capacitated multiflow. We show a min-max theorem which extends
Lov\'{a}sz-Cherkassky theorem to the node-capacity setting. Our results build
on discrete convexity in the node-connectivity terminal backup problem.
