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

Figure 15.6 SIP network-based call control for fixed-mobile convergence

Though much as been written about fixed-mobile convergence, as shown in

Figure 15.6, this is a natural application for SIP call control placed on the Inter-

net. In this diagram, all communication devices on all possible networks are

considered SIP endpoints:

1. PC/laptops and SIP phones on IP LANs


2. Mobile SIP devices on Wi-Fi (and WiMAX in the near future) networks


3. 2G and 3G devices as they appear on the Internet side of mobile-
   Internet gateways


4. PSTN and PBX phones as they appear on the Internet side of TDM-
   Internet gateways

An adequate SIP mobile device can also act as a virtual PBX phone in the

enterprise with proper support for PBX-like voice services on the Internet-

based SIP server and strong security precautions, such as those discussed in

Chapter 9, “SIP Security.”

The main challenge for network-based SIP mobility and fixed mobile inte-

gration is for the Internet-based SIP server shown in Figure 15.6 to get access

to the gateway service providers to connect to 2G/3G mobile networks and to

the PSTN gateways. Besides the technical issues of call control and security,

bilateral business arrangements are also required, such as developed in the

IETF SPEERMINT WG [14].

Internet

SIP Mobility

Wireless LAN

CPE

Wireless

Network

GWYs

Voice

GWY

2G/3G

Wireless

Networks

PSTN

Voice

SMS

3G IM

3G Presence

1

WISP

2

3

Bi-modal:^4

WLAN & 2G

262 Chapter 15