3.7 Classification of Dynamic Call Routing Schemes

In general, dynamic routing schemes can be classified in the following ways:

	Centralized vs. Distributed: In the centralized system, routing computation is performed at a centralized processor.
	Time-Dependent vs. Adaptive: Time-dependent routing refers to updating of the routing table at a certain time (once a day or once a week) for a preplanned set of routes a call can attempt while the set of routes may vary from one time period to another. Adaptive routing refers to frequent update (in min or sec) of the routing table based on traffic measurements or on events.
	Periodic vs. On-demand: Within adaptive routing, the routing table update can be performed on a periodic basic, or on-demand.
	State-Dependent vs. Event-Dependent: State-dependent refers to considering the state of a network in determining a routing decision; typically, state here refers to the state of a link such as available capacity or just availability, or some notion of a cost. Event-dependent refers to selection of a new alternate route if a certain event occurs.
	OCC vs. PCC: DNHR and RTNR are based on OCC, while DAR and DCR are based on PCC. An intertwined feature with OCC and PCC is crankback.

3.7 Classification of Dynamic Call Routing Schemes

Despite the above classification, all dynamic routing schemes have two things in common:

	All routing schemes allow at most two links for routing a call.
	They all provide trunk reservation. If the network is fully connected, a call tries the direct link route first, although dnhr or rtnr does not require it; if it is not fully connected, a preferred two-link route is usually determined as the first attempt path for the demand pair that does not have a direct link.

3.7 Classification of Dynamic Call Routing Schemes