Abstrakt

In wireless networks mobile clients change their physical location, which results in changing point of attachment to the network. Such handovers introduce unwanted periods, when node does not have communication capabilities. Depending on many conditions, such events may require reconfiguration of layer 2 (e.g. IEEE 802.16) or both 2 and 3 layers (IPv6). This paper investigates delays introduced in the latter type of handover. IPv6 protocol family supports two automatic configuration modes: stateless (SLAAC) and stateful (DHCPv6). Both modes may be used in wireless networks. Once the L2 handover procedure is completed, the mobile node (MN) starts its IPv6 configuration process, using stateless (router advertisements) or stateful (DHCPv6) mode. When care-of address (CoA) is assigned, its uniqueness has to be verified, using Duplicate Address Detection (DAD) procedure. Depending on a network type, this procedure may even take more than 1000 ms. The obtained CoA can be used only when configuration and DAD procedures are completed for informing corresponding nodes about new MN location. Such delay introduces unacceptable gaps in communication capability. This paper proposes several new mechanisms that enable faster IPv6 reconfiguration. First proposal allow MN to obtain its IPv6 address and other configuration options in advance, before completing actual handover. Such a priori knowledge about configuration available at destination locations may be exploited to speed up configuration process itself and also allow initiating Mobile IPv6 operations earlier, thus further shortening delays. Another proposal includes new way of delivering routing information to MN, using DHCPv6. Mechanism itself and its verification techniques are discussed. Results of extensive simulations, statistical analysis as well as areas of further study conclude this paper.

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