ual equipment and hardware that comprises the network and other related resources, such as IP addresses, telephone numbers and Web space or server memory and disk space. Logical inventory consists of things that do not physically exist but can be defined, configured and inventoried, such as circuits or virtual network paths. Logical inventory provides a view of how the network is configured into services, and how the physical network links to the customer. Network inventory systems track two major types of physical network inventory: those elements that are deployed on the network and those that are stored in a warehouse. Drilling deeper, network inventory systems should also track any network components leased from or supplied by other IICs. For example, a data services provider may serve buildings to which its network is not physically connected. In such cases, the IIC might lease The Ultimate Guide to Building and Delivering OSS/BSS facility circuits from an ILEC over which it will provide value-added services. From a services point of view, that leased circuit is an accessible network resource, i.e. available inventory, and will be treated as such by the network inventory system. As mentioned earlier, network inventory systems play a critical role in the ordering process, letting sales representatives and customers know if and when requested services are available to specific locations. If a service is requested for a location but the serving end-office does not have the right equipment installed, the inventory system should automatically report if the equipment is available in the warehouse. If it has been ordered from the manufacturer but hasn't been delivered, the system, ideally, should note when it will arrive and when it's scheduled for installation. Similarly, going back to the T-1 service example provided earlier, the network inventory system would track locations' facility circuits that have been implemented, whether or not those circuits have yet been configured, and how much capacity remains availa