Chapter 9: User Mobility in IP Networks: Current Issues and Recent Developments

Bj rn Landfeldt, Jonathan Chan, Binh Thai, and Aruna Seneviratne

9.1 Introduction

The introduction of wireless networks to the Internet infrastructure will bring many changes to the way we use and relate to computers. Wireless networks have many potential advantages such as lowering of installation and deployment costs, but the biggest impact will come from users becoming mobile.

The mobility factor has proven itself one of the most-successful features in modern telephony. The advent of cellular telephony clearly showed the demand from users, who have been willing to pay a considerably higher price for telephony services if only they could be mobile. There has been unprecedented growth in customer bases in most if not all rolled-out cellular networks, and regions such as Scandinavia have almost full geographic coverage, making telephony ubiquitous. A similar success story can be seen in Japan, where NTT Docomo's i-mode system has brought mobile data services to the Japanese public. With i-mode, similar to pure cellular telephony networks, the growth in customer base has been unprecedented for data services.

The deployment of GPRS and 3G networks will bring packet switching to cellular terminals. This will create an integration of mobility and data services, and lay the foundation of the mobile Internet. Cellular technologies, as is the case of 2G networks, provide a wide range of coverage from local to wide area. The data rates of these networks are modest at present, but are expected to increase considerably over the next few years. However, it is difficult for cellular technologies to compete with wireless LAN (WLAN) solutions in terms of providing high data rates. The costs involved with the two technologies also are very different. Cellular networks are inherently more complex than WLANs and use licensed spectrum. Therefore, it is more costly to run traffic through these networks.

This has lead to the emergence of a market for WLAN in so-called hot spots. This market segment consists of areas of predictably high mobile user densities such as hotels, airports, and conference centers. At these locations, wireless coverage through the IEEE 802.11 WLAN standard is being rolled out and offered to the general public. This standard is being widely deployed in enterprise networks, as well as gaining momentum in the home network market segment. Together, the cellular and WLAN technologies constitute the base needed for the emergence of the mobile Internet. Users will have ubiquitous access through a variety of access networks as they move around geographically.

There are many forms of mobility and all play a role in the mobile Internet. By user mobility we mean the ability of users to either move geographically or to change access points in the Internet by either updating the destination IP address or to change the routing of packets to the destination address. There are other forms of mobility as well. For example, teleporting ^[1] is an example of presentation mobility where the applications are executed on one host but the presentation (screen output) can be moved between computers as the user requires. Another example is applications that can maintain states while hosts are disconnected from the network. For example, many FTP clients can maintain states if the network connection disappears and resume the file transfer when another connection is available even if the terminal has a new address. In this chapter, we focus on user mobility because it is fundamental and critical for the success of the emerging mobile Internet.

^[1]Richardson, T. et al., Teleporting in an X window system environment, IEEE Personal Communications Magazine, 1(3), 6–12, 1994.