Change the arrow line's default to be a line with an open circle at each end (see Drawing Lines Using Defaults). If you want to draw a directed network, select an arrowhead for the centre of the line. The arrow line tool will now allow you to easily draw a network diagram. If you right click on each arc of the network diagram, you can enter any text you require and it will be angled to suit the line.
Video - Drawing Networks Using Default Lines