SIP Device-Based Fixed-Mobile Convergence
An increasing number of SIP endpoints have more than one network interface.
This was initially the case with laptop computers but has now also spread to
pocket computers, PDAs, and mobile phones. Following are the possible net-
work interfaces:
■■ 802.3 wired LAN connection
■■ 802.11 a/b/g wireless LAN (Wi-Fi)
■■ 2G and 3G radio connectivity
■■ Bluetooth radio
■■ Emerging 802.16 wireless MAN (WIMAX)
■■ New standard radios such as Ultrawideband technology 802.15 (UWB)
and proprietary systems such as xMAX radios
A SIP device with several network interfaces is also called a multimodal
device. Multimodal devices could support the control for selecting the service
and features to the end user, the owner of the device. This has tremendous
implications for the business models of facility-based mobile services. We will
not discuss here all the business and regulatory implications from the emer-
gence of mobile SIP multimodal communication devices but will rather focus
on the technical challenges in the section, on “Multimodal Mobile Device
Technology and Issues,” later in this chapter.
SIP Application-Layer Mobility and Mobile IP
Mobility on the Internet can be provided by Mobile IP (MIP), see [15]. SIP and
Mobile IP (MIP) differ however in a fundamental way:
■■ Application-layer mobility based on SIP deals with the changing IP
address to keep the applications working. SIP application-layer mobil-
ity works only for the applications for which it has been designed; in
this case, for real-time communications only.
■■ Mobile IP presents to the applications the same IP address, though the
actual IP address in the network may have changed. Mobile IP works,
therefore, for all applications, including file transfer, e-mail, and the
web, for example.
As can be seen in Figure 15.7, the triangle routing may introduce undesir-
able extra delays for real time media like voice.
SIP Application Level Mobility 263