tage of the deployed local access architecture. Some IICs pursue "overbuilding" strategies, delivering fiber optic network access directly to the customer's premises. Overbuilding is generally focused in urban and other high concentration corporate areas and, as the economics allow, is becoming a superior access option to services such as DSL or T-1. Cable infrastructure is increasing in its importance, particularly for residential Internet access and voice services. We will discuss the details of delivering cable-based IP services later in this chapter. From a supply chain The Ultimate Guide to Building and Delivering OSS/BSS perspective, local cable infrastructure currently is the only means of providing access to Internet services that even remotely competes with the local telephony infrastructure in terms of penetration and footprint. As more and more Internet traffic moves to mobile devices, cellular or mobile networks can be considered part of the local access infrastructure. Though playing a very different role from landline networks, mobile networks will provide key links to customers for those services intended for the mobile environment. Backbone Networks. Backbone networks encompass a number of different types of networks, including the Internet, long-distance networks and other closed-data networks. The global network is evolving SO that the boundaries between the Internet and other backbone networks, including voice networks, are becoming tougher to identify. Physically, numerous entrance and egress points exist that connect these networks together. For example, VoIP gateways link voice networks to IP networks, including the Internet. Massive corporate intranets generally touch the Internet, but are protected by firewalls and other security mechanisms that monitor traffic as it flows across the interface point. Many backbone network service providers, or NSPs, host massive data and switching centers that provide co-location services to other IICs of all kinds. Essentially, these centers provide direc