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After the overview on SIP-based IP communication services presented in
Chapter 2, we will provide here a brief summary of the Internet architecture
(from the perspective of real-time communications) by contrasting it to the
telecom-style circuit-switched networks. This review will facilitate an under-
standing of the chapters that follow.

Telecom Architecture

We refer readers to the numerous references available on ITU-T telecommuni-
cations networks. The complete, original, and up-to-date documents are avail-
able to be purchased from the ITU-T at the following address:

http://itu.int/home/index.html

Other relevant documents (such as for Frame Relay, ATM, and Multiproto-
col Label Switching (MPLS) networks) can be obtained at no cost at the
following address:

http://www.mfaforum.org

Figure 3.1 shows the architecture of all ITU-T-style circuit-switched networks.

Architectural Principles

of the Internet

CHAPTER

3