5 Connection-Oriented, Connectionless and Virtual Circuits 18.2.6 Reliable Network Service 18.2.7 Unreliable Network Service 18.3X.25 18.3.1 X.25 Network and Packets 18.3.2 Packet Switches VS. Routers 18.3.3 PADs: Network Interface Devices 18.3.4 X.25 Protocol Stack 18.3.5 X.25 Performance 18.4Frame Relay 18.4.1 Improvements on X.25 18.4.2 Relaying Frames Instead of Switching Packets 18.4.3 Unreliable Service 18.4.4 TCP/IP and Frame Relay 18.4.5 Frame Relay Performance 18.4.6 Committed Information Rate (CIR) 18.4.7 Burst Information Rate (BIR) 18.5QoS Requirement for Voice in Packets 18.6ATM 18.7MPLS 18.8TCP/IP Over MPLS PAGE 13 TELECOM 101 REFERENCE BOOK TERACOM TRAINING INSTITUTE 19 IP NETWORK SERVICES In this chapter, we focus on two primary services that can run on an IP/MPLS network: voice and secure data communications. We'll begin with an introduction to Voice over IP components, jargon and buzzwords, and understand how VolP will mesh with the PSTN covered in Part 1. You'll also understand how IPsec protocols and equipment implement IP VPNs for secure business data communications over IP networks. 19.1 VolP System Components 19.2VolP over the Internet: VSPs 19.2.1 Why Internet Telephony is Cheaper than POTS 19.2.2 DSO Interconnect to the PSTN 19.3Internet Telephony from LEC / CATV 19.4Managed-IP Telephone Service (MIPT) 19.5VPNs 19.5.1 Customer-Premise-Based VPNs 19.5.2 Carrier VPN Service 20 UNDERSTANDING THE INTERNET Let's not forget the Internet! This chapter provides a concise explanation of the Internet, reviewing past and present, ISPs, who pays for it, TCP and IP, SMTP and MIME for e-mail, HTML, Web servers and browsers, the Domain Name System and more. We'll complete the picture with practical guidelines for connecting. 20.1 Internet History 20.1.1 Philosophy Behind the Internet 20.1.2 How Al Gore Invented the Internet 20.1.3 Historical Limitations 20.2Internet Basics 20.2.1 Globally-Meaningful Network Addresses 20.2.2 Connectionless Network Service 20.3Internet Today: Internet Service Providers 20