g drop off a Customer Premise Equipment (CPE) access device (for example, a DSL, cable modem, or a low-end router), which connects with Ethernet to the customer's routing or switching equipment. This connection model is shown in the "Small Business" model in Figure 7-1 using an Integrated Access Device (IAD). It is important to note that only service providers that have complete control over the QoS of the physical connection can offer business-class voice services over a SIP trunk. VoIP services that ride on non-QoS enabled networks owned by a separate Internet provider cannot provide guarantees of quality levels because they do not control the sequencing of packets on the physical medium of delivery into your premises. Physical connection options include Ethernet, DSL, cable, wireless (3G cellular), and tra- ditional T1/E1. IP Addressing The configuration of a SIP trunk requires coordination between the enterprise to config- ure its border element and the service provider's border element before starting to exchange SIP traffic. The provider allocates either explicit IP addresses or access via Domain Name System (DNS). For dedicated voice-only connections, most providers allo- cate two addresses per SIP trunk, whereas some offer more. If only two addresses are provided, these can often be used (per agreement with the service provider) in either a primary-secondary failover or a load-balancing algorithm. For integrated data and SIP trunk services, there is often a single IP address. Several serv- ice providers that offer both data and voice over a single IP interface also offer Multiprotocol Label Switching (MPLS) services and require that voice be sent with an MPLS label. This setup enables the service provider to terminate voice traffic, whereas data traffic marked with a different label can be tunneled through the network. Dial Plans and Call Routing Adding a SIP trunk service to your network most likely means there are service changes (accessible numbers and their associated cost), and you should optimize ca