... Enterprises 6 8IP- Based Endpoints: Desktop and Conference Phones, 6 9IP- PBX, IP Centrex, and IP- Based PBX Tie Lines, 7 1IP- VPN and VoIP for Tele-Workers, 77Web-Based Call and Contact Centers, 79Next-Generation ... (DSL)-type con-nections to facilitate data communications over the Internet. This current modeFigure 1-2 A network configuration for supporting phone-to-phone, PC-to-phone, andPC-to-PC real-time voice ... 2-8 Protocol layers for SIP-based real-time voice services using the IP. PACKET VOICE TRANSMISSION23or the integrated access device (IAD), it is possible to use either voice overATM or VoIP over...