P addressing space such as the Internet or a signaling aware network address translation (NAT). Utilizing the Internet as the method to interconnect does not ensure any quality of serv- ice (QoS) guarantees, and as such there is no capability to ensure that the service can occur at the required level of quality. One workaround for this is the use of a shared MPLS network, as shown in Figure 2-4. In this arrangement, two companies share the same MPLS provider. This allows a reasonable expectation of a high quality of connec- tion between the two companies' MPLS networks. The interconnection of the MPLS net- work would traverse only a single SP network, and that SP would have a service level agreement (SLA) with each of the enterprise customers. This generally leads to a reason- able high level of expectation of a good QoS. Class Four TDM Ports Deployed by Carriers Interconnect Method Session Border Controllers Deployed by Carriers Figure 2-4 Interenterprise Connectivity Methods 24 SIP Trunking When utilizing this shared trunking service between federated enterprises, the use of nonvoice services is a natural extension. The only widely used current method of video conferencing between enterprises is ISDN video endpoints and H.320 services. These ISDN video endpoints share the same E.164 universal addressing as regular PSTN phones and have a level of interoperability that enables video calls between unaffiliated net- works. The downside of these types of networks is that they have been purposely built by SPs. Specifically routing ISDN video calls, which are identified at signaling time over specific circuits to ensure connectivity, leads to much higher costs, as compared with IP routing. This higher cost has lead to a much lower adoption rate. The use of a border element at each enterprise and simultaneous connections to an MPLS network for each enterprise in combination with a routable IP address at the edge of each network is a growing trend for interenterprise connectivity via SIP trunks. Feature Trends in SIP Tr