Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Figure 3.2 IMS reference architecture

Courtesy R. Stastny, ÖFEG

Besides such features illustrated by the architecture diagram for the IMS in

Figure 3.2, the following are several other telecom standards procedures:

■■ Detailed standards documents are developed before research and trials

of experimental systems.

■■ Telecom standards documents usually do not bear the names of their

authors and are considered to have been issued by organizations, often

driven by marketing departments.

■■ Telecom standards are driven by commercial business models and the

constraints of time-to-market. As we will see later in this chapter, Inter-

net standards have very different drivers.

Internet Architecture

The engineering of Internet communications differs in many ways from

telecommunications engineering. We will quote the relevant passages from

RFC 1958, “Architectural Principles of the Internet,” [2] by Brian Carpenter

and reproduce some paragraphs, since we find it impossible to articulate the

issues in any better way.

Application Servers Changing

Functions

PSTN

Emulation

(R2)

IMS/

PSTN

Simulation

IP Transport (Access and Core)

Other IP Networks

PSTN/ISDN

Network

Attachment

Subsystem

MG

Resource &

Admission

Control

Resource & Admission

Control

UE

AGCF

P1

Gm Gd

Gd

e4

Re la

Mp Mn

le

Ut

Ut Rf/Ro

Rf/Ro

P3 lb

lw

Gd

Sh

Cx

ISC Dh

Dx

Mw/Mk/Mm

Mw

Mw

Mr

Mg

Mi

Mj

P2

e2

Mk

Mk

CNG

BGCF

P-CSSF MRFC MGCF

SPDF

MRFP

RCEF BGF

T-MGF

A-RACF

SGF

SPDF

IBCF

I-BGF

UPSF SLF IWF

I/S-CSCF

42 Chapter 3