Wireless Data Communications Mobile IP

As the convergence of voice and data continues, a more discreet change is also coming  into play. While data is considered fixed to a location, the end user is now more mobile. This opens a new set of challenges for the industry and manufacturers alike, because of  the need for mobility. What once was a simple procedure of connecting the user’s modem to a land line now poses the need to connect that same user to a device while mobile. Protocols need to be more flexible, accommodating the mobile user as the device is  moved from location to location. Moreover, the physical devices (for example, the modems) must be moved often. In a dial-up, circuit-switched communications  arrangement, this is not a major problem. The user can unplug a modem, reconnect it to a landline elsewhere, and dial from anywhere.

However, when we use IP as our network protocol, data is routed based on a network/subnetwork address. Routing tables keep track of where the user is located and route the datagrams (packets) to that subnetwork (see Figure 23-1). When a mobile user logs on and attempts to dial in to the network, the IP address is checked against a routing table and routed accordingly. Updating the tables can be extremely overhead intensive, and it can produce significant amounts of latency in the Internet or Intranet. Using an  ICMP Route Discovery Protocol(IRDP), which is part of the TCP/IP protocol suite,helps. However, when the IRDP process updates its tables, we use a lot of bandwidth. Figure 23-2is an example of the IRDP process where a message is generated by a host to learn all routes available to get to and through the network.

Something needs to be done to accommodate the use of mobile IP by an escalating number of users wanting to log on anywhere. Of course one solution is to use the Dynamic Host Configuration Protocol(DHCP), which uses a server-based mechanism to allocate a new IP every time a user logs onto the network or assigns a static IP address to a user who may be using a diskless PC. The purpose of the DHCP was to facilitate the mobile or not permanently attached user in an ISP network where addresses are limited and casual users are the norm. So the industry had to arrive at a solution allowing casual and nomadic users the same access while they travel (roam) as when they are in there fixed office location. Figure 23-3shows the growth curve of wireless data users attempting to use mobile IP and wireless data communications over the past couple of years. In this graph we see that the numbers justify the concern and the effort being afforded to the problem. The number of wireless users in the world is escalating and the 500 million users shown in this graph are conservative estimates. We are living in a mobile society where users want their data, when they want it, where they want it, and how they want it! What percentage of these wireless users will want data over their connection remains to be seen. However, early estimates are that over one-fifth will want their data in a mobile environment