xbt::signal<void(Link const&)> Link::on_destruction;
xbt::signal<void(Link const&)> Link::on_state_change;
xbt::signal<void(Link const&)> Link::on_bandwidth_change;
xbt::signal<void(Link const&)> Link::on_destruction;
xbt::signal<void(Link const&)> Link::on_state_change;
xbt::signal<void(Link const&)> Link::on_bandwidth_change;