Internet Basics technology because they need to provide business-grade services with guaranteed quality of service (QoS), and they need to perform the highest class of traffic engi- neering to ensure maximum network performance. From here, various ISPs are connected to create the Internet (see Figure 8.9). There are various levels of ISPs. For example, backbone ISPs serve at the highest level of the hierarchy and provide connectivity between the tens of thousands of ISPs worldwide. Below them are several classes of ISPs, including those that may cover a large area and support both business customers and basic consumers as well as local ISPs that more commonly serve small communities and focus on rock- bottom prices for consumers rather than business-class services for enterprises. ISPs compete based on brand name, value-added services, performance, reli- ability, price, customer service, and other factors. Global Internet connectivity depends on private cooperation between ISPs. ISP cooperation, in turn, requires agreements about the business relationship, physical interconnection (called peer- ing), ability to exchange routing information (e.g., via BGP), ability to exchange data, and the payment policy. As Figure 8.10 shows, lower-level ISPs or local providers connect to higher-tier ISPs, which connect to the global Internet. ISPs exchange each other's customer Backbone Backbone Provider Provider Subscriber Subscriber Cable ISP Subscriber Dialup Subscriber Subscriber Subscriber = Exchange Point Figure 8.9 Internet composition Chapter 8 The Internet and IP Infrastructures Global Internet Higher-Tier ISP Routes to Internet Local ISP X = Routes for ISP X's Customers Figure 8.10 ISP transit architecture routes and share the costs. Smaller ISPs pay a transit fee to larger ISPs for access to global routing tables. Internet Addressing and Address Resolution To make the Internet an open communications system, a globally accepted method of identifying computers was needed, and IP acts as the formal addressing mechanism 