In mathematics the term 'subtended' usually refers to the direct relationship between an angle and its arc length. For example, according to circle geometry, in a circle equal angles subtend equal arc lengths. The converse is also true, equal arc lenghts subtend equal angles.
A central angle is an angle whose vertex is the center of a circle, and whose sides pass through a pair of points on the circle, thereby subtending an arc between those two points whose angle is (by definition) equal to the central angle itself. ...
Subtending allows you to use one ATM backbone for multiple Cisco 6100/6130 chassis.
Subtending is a Cisco 6100 Series system feature that reduces the cost per subscriber by amortizing the expense of the network interface module and the edge switch port connection over a large number of subscribers.
You can subtend up to six Cisco 6100/6130s to one subtending host Cisco 6100/6130 that is connected to the ATM network backbone (refer to Figure 5-1).