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Planning and Implementing Wireless LANS
By Peter Rysavy
Making Network Software and Applications Work
So we now know how wireless LANs work and how they interconnect with other networks. But what is involved in making network systems and applications work? Fortunately this is straightforward. In this section we look at the protocol stacks involved, where Mobile IP might make sense and how to configure applications for optimal performance. Protocol Stacks We have already discussed how wireless LANs use physical and datalink layer protocols that are specialized for the finicky wireless environment. But from the network layer up, traditional networking protocols function with no modification required. This mea ns that virtually all mainstream networking systems are supported, including:
If your roaming wireless users sit down, turn on their portable computers, establish a wireless networking session, conduct their business, log off and then turn off their machines, mobility may not be an issue, especially if the users obtain IP addresses dynamically using Dynamic Host Control Protocol (DHCP). But if IP network users keep their machines on, perhaps use handheld computers and wander from one area to another, they may ultimately connect with an access point that is connected to a different subnet. Because IP addresses by design refer to a particular subnet, IP traffic will not be able to find its way to the new location. This is where Mobile IP enters the picture. A recently completed Internet standard, RFC 2002, Mobile IP provides a mechanism by which hosts belong to a "home" network. When the host roams to a new network, it registers with its home agent. The home agent then intercepts traffic sent to the mobile node, encapsulates it in another IP packet, and forwards it to a foreign agent, a special node (installed in a workstation, router or a ccess point) which forwards the packets to the mobile node. Traffic originated by the mobile node can travel back directly and does not have to be sent via the home node, resulting in triangular routing of traffic.
For more information on Mobile IP, see Internet To Go, Now With Mobile IP by Peter Rysavy. Almost any application that works over a wired LAN should work over a wireless LAN. The only thing you may want to do differently is to consider the size of applications and the speed of the network. If a user is operating on a 1-Mbps network and is loading a 5-Mbyte application from a file server, the application could take over a minute to load. It is usually better for users to have copies of frequently used applications, utilities and data files on their own hard drives rather than on file servers.
Updated January 14, 1998
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