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Prof. Dr.-Ing. habil. Andreas Mitschele-Thiel


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"A New Framework to Support Mobility in Multi-hop Hybrid Networks", Proceedings pp.51-52, 51st IWK – Internationales Wissenschaftliches Kolloquium, Ilmenau, Deutschland, September 11 - 15, 2006

Dr. Ausama Yousef
Prof. Dr.-Ing. habil. Andreas Mitschele-Thiel
Dipl.-Ing. René Böringer
Dr.-Ing. Ali Diab
Connecting wireless devices to the Internet is of major interest in today’s research. It is
well known that the Wireless Local Area Network (WLAN) is a widely deployed standard
[1] which will play a major role in future communication networks. WLAN can be
deployed in infrastructure or infrastructure-less mode, referred to as ad hoc [2].
WLAN offers high bit rate services. However, it is difficult to avoid not covered areas. To
overcome this, a Mobile Host (MH) could use an intermediate MH as a relay to the
Access Point (AP). This leads to the so called hybrid multi-hops network structure, which
can be created by enabling mobility support between infrastructure and infrastructureless
networks. In order to achieve this, new adequate solutions for inter-connecting
infrastructure-based networks and ad hoc networks should be developed.
Several proposals have been published. In [3] an approach describes how to connect a
wired IP networks running the protocol Mobile IP (MIP) [4] with ad hoc networks running
the Ad hoc On-Demand Distance Vector routing protocol (AODV) [5]. In [6] a scheme is
introduced to develop a new integrated solution for IPv6-based hybrid multi-hops
network by using Cellular IP in the IP core and AODV in ad hoc networks. A gateway to
interconnect ad hoc networks and wired IP networks is presented in [7]. It extends MIP
to manage multi-homing where network layer characteristics are used to decide the
care-of address.
However, in the previous solutions the latency required to resume the session is a main
disadvantage. This latency has negative impacts on the Quality of Service (QoS).
Therefore, it is necessary to develop new solutions to support seamless mobility in
hybrid multi-hops networks.
Throughout this paper we propose a new solution to achieve a fast handoff in multi-hop
hybrid networks. We extend AODV to use the principle of fast authentication as it is
described in Mobile IP Fast Authentication Protocol (MIFA) [8]. When the MH wants to
connect to the Internet it connects itself with the AP through multiple wireless hops and
uses the MIP protocol to register itself with its Home Agent (HA) through the serving
Foreign Agent (FA).
The MH may move inside the same ad hoc network while staying connected to the same
AP or may move to another AP. If the new AP belongs to the same subnet as the old AP
the changes are restricted to the ad hoc network. A link to the new AP is established
without any changing in network layer. However, if the AP belongs to another subnet,
the principle of local fast authentication is used to accelerate the handoff. The MH only
proceeds an authentication procedure with the new FA and becomes connected to the
Internet. In the case the fast authentication can not be used a new FA has to request the
state information from the old FA. During the handoff the old FA sends the packets,
destined to the MH, to the new FA. We have specified the protocol extension by means
of Message Sequence Chart (MSC).
Currently, we develop a mathematical model to evaluate the performance compared to
other proposal. The first results show that our proposal outperforms the others presented
in the literature with respect to the handoff latency and expected number of dropped
packet. We are able to achieve seamless and fast handover in multi-hop networks. This
will lead to match the requirements of real-time applications.