If you have the responsibility to design, upgrade and manage data networks to carry IP Telephony (voice, video and data); need help in evaluating competing IP-Centrex and IP-PBX systems; or need guidance in specifying the parameters for a service level agreement for IP-Centrex, this unique reference provides you with the knowledge you need to get the job done right. It enables you to more accurately estimate the time and resources needed to implement IP Telephony in your organization. The book describes the IP-Centrex option of having the telephone company take responsibility for the service delivery and offers the kind of information service providers need to improve marketing and sales campaigns for IP-Centrex services.