TKK | Tietoverkkolaboratorio | Opetus
In the near future Internet terminals will also get smaller and people will be using more handheld personal computers. The new networks, mainly GPRS and UMTS, make it possible for the terminals to have an instant access to the net without billing the user. This means that the terminal needs to know how to make access point (AP) handoffs when it notices two APs and e.g. the signal strength and the free bandwidth are better than in the other AP. In GSM networks this problem has already been solved, but when using hierachical packet protocols (IP or IPv6) APs are in different network segments and packet delivering to mobile hosts is not straight forward.
Consider two IP subnets with addresses 10.128.1.0 and 10.128.2.0. Let us assume that there are APs in both nets with addresses 10.128.1.100 and 10.128.2.200 and the mobile node (MN) with IP 10.128.1.50 in the first subnet.
If the IP of the MN is static and the user moves the node to proceed the handoff between two APs it can be clearly seen that the MN's IP will be in a wrong subnet.
In the other case MN could change its IP to correspond to the new network, but this would cease all the streams to the node, because packets targeted to node's old address wouldn't be received.
In IP networks, there is a solution for this problem and it's called Mobile IP. The basic idea in it is to register the MN with a router in a network where the node is most of its time (home network). The node itself has a dynamic IP (careoff address) and every packet sent and received to it will be delivered through its router. When the node changes its network it gets a new dynamically assigned address and the new address is reported to the router. Every packet from the originating host is actually targeted to the router which then delivers packets to MN.
This solutions generates useless traffic in a case MN and a server are in the same network (not in the home net). Server is sending data to MNs home network where the router forwards every packet back to the originating network.
This problem has been solved in IPv6 protocol stack. There is a space reserved for a routing header in IPv6 header which can be used to inform the server about the MNs new dynamic address and packets needn't to be routed through the home network.
0.1 Introduction
1.0 Internet
2.0 Services
3.0 Advantages and Disadvantages
Antti Hätinen (AH)
Li Yaohui (LY)
Martti Mela (MM)