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Conclusions
At present, new issues of high-speed network research emerge from the convergence
of wireless and wired next generation networks and the planned deployment
of new integrated multi-media and Web services. In our paper we have sketched
the concept of a service architecture where adaptive applications are running
above a distributed service management and QoS-control layer on top of
the transport and network layers with their corresponding resource allocation
and control as well as mobility-management functionalities. We have described
a LINUX implementation of our concept in an IEEE802.11b compatible wireless
LAN with Mobile IP as network layer using a unified programming model.
Furthermore, we have investigated the efficiency of the data transport
by the TCP and UDP protocols. By appropriate measurement tools we have
illustrated the impacts of the changing transmission quality, the resulting
error recovery of the wireless data link layer and the roaming between
different basic service areas on the dynamics of TCP flow control and on
the resource-reservation process taking into account realistic emission
patterns of the IP frames. Moreover, we have identified the most effective
and sensitive control information of the adaptation process.
Finally, we want to point out some important issues regarding the interworking
between resource reservation, QoS-control, mobility- and security-management
that require an improved, more efficient solution in the near future. From
our experiments, one can conclude that an interworking between the TCP
flow-control and the behavior of the wireless DLC layer should be organized
to improve the throughput and delay characteristics of the data flows while
moving and roaming, e.g. by exchanging management and control information
that optimizes an ECN-based TCP flow-control in a way similar to the ABR-scheme
in ATM (cf. [26]).
The use of improved TCP variants, e.g. those that freeze and recover the
congestion-window state after a handoff, that use TCP control block statistics,
that mimic a loss-less PDU transfer at the data link layer like snoop or
that distinguish different sources of packet loss may be another alternative
(cf. [6], [29]).
Furthermore, we have demonstrated, despite all technical shortcomings of
our implementation, that micro-mobility is not supported in an adequate
manner by the current functionality of Mobile IP. Cellular IP, route and
address caching techniques, improved movement detection by eager or hinted
cell switching and fast or two-phase handover schemes may partially resolve
the observed difficulties (cf. [8],
[14], [16]).
In conclusion, we think that the realization of our concept and the
measurements clearly reveal the potential and drawbacks of the mobile-aware
approach and provide new insight on the relationship of the signal-to-interference
ratio, the delay-loss characteristic of flows and the TCP behavior as well
as the adaptation processes. They may also be used to develop improved
handoff and TCP flow-control mechanisms as well as improved mobile-aware
applications for an efficient transport of real-time multi-media and interactive
Web services in next generation wireless networks.
Next:BibliographyUp:Mobility
and QoS-Management forPrevious:Performance
analysis of the
Bachmann
2002-02-21