Handover in All-IP Mobile Networks
|Handover describes a mechanism in cellular networks that transfers
the association of a mobile end system from one base station - which is
presently active - to a new base station. In general handover is applied
when a user moves through the coverage area of a cellular network and crosses
cell boundaries. The handover between wireless cells of the same type (in
terms of coverage, data rate and mobility) is often referred to as horizontal
handover, whereas the handover between wireless cells of different type
is characterized as vertical handover.
In the Internet Protocol (IP) suite the IP address of an end system
identifies a host uniquely and also the IP subnet to which the host is
attached. Therefore the meaning of the IP address is twofold: end point
identification and location identification. When a host changes its point
of attachment the IP address must be modified in order to route packets
to the mobile's new subnetwork. Unfortunately, ongoing TCP connections
break since the IP address is part of the TCP connection identifier and
used at TCP connection setup.
Traditional IP-based mobility approaches, such as IETF Mobile IP, were
designed with respect to horizontal handover. Thus, the vertical handover
and other new services and network architectures pose new requirements
on handover design. In our research on handover in All-IP mobile networks
we concentrate on these requirements and try to develop new solutions for
the problems and challenges arising out of them.
2. Main Research Interests
|Our main research interests in this area can be structured into the
The following sections give more informations about these topics.
Evaluation of Existing Approaches
Security Issues of Handover in Roaming Scenarios
2.1. Evaluation of Existing Approaches
|Recent reserach-oriented handover approaches will be evaluated, such
as IETF Mobile IPv4,
Exensions of IETF Mobile IPv4 (Hierarchical
Foreign Agents, Extensions
by MosquitoNet), IETF
Mobile IPv6, Multicast-based handover, HAWAII
, Cellular IP, Mobile
People Architecture, ICEBERG,
SIP Mobility. A performance evaluation will be performed for selected
approaches. This approaches will be compared with respected to handover-specificic
performance metrics, such as handover latency, packet loss and others.
The performance evaluation will be done by measurement in a testbed (see
below) and by simulations, respectively.
2.2. Multicast-Based Handover
|In order to solve the IP mobility problems two main approaches can
be identified: Address Translation and Indirect Routing (e.g. IETF
Mobile IP) or Location-Independent Addressing and Routing. Interestingly,
there is already an approach which supports addressing and routing independently
of the host's location - multicast. Its ability is similar to the
requirement of mobility support, though in a different context. MOMBASA.
MOMBASA stands for 'MObility support - a Multicast-BASed Approach'. MOMBASA
intends to utilise multicast in order to support network-level mobility.
In relation to the classical approach of Address Translation and Indirect
Routing, MOMBASA has three main advantages:
Even for vertical handover the usage of predictive mechanisms, such as
registration in advance and predictive data distribution, decreases the
handover latency and packet losses. The realization of these mechanisms
with multicast is very natural. The today's IP multicast protocols fit
well for 'broadcast-like' applications although there are a number of open
issues to solve. But handover has requirements similar to 'narrow-cast'
applications. Such 'narrow-cast' multicast protocols are matter of research
and it is expected that the future Internet will provide an optimised Multicast.
MOMBASA works out the requirements of handover on future multicast protocols
and investigates alternate multicast protocols (e.g. CMAP/CMNP,
Small Group Multicast,
for their application to host mobility.
Rerouting for handover is done in a network node where the path to the
old and from the new base station diverge (and not in a software agent
in the mobile's home network according to the Mobile IP approach).
No "handover-specific" signalling and infrastructure is required, instead
multicast is reused for mobility purposes.
MOMBASA minimises the handover latency. In the utmost case packets are
distributed in advance to potential new base stations which buffer the
packets. In this case the usage of multicast provides the efficient distribution
of data to multiple base stations.
2.3. Security Issues of Handover in Roaming Scenarios
|As the mechanisms and protocols developed to realize mobile communications
also open up new ways for attacking ongoing communications as well as subscriber
fraud, specific attention needs to be paid to the security issues of handover
design. The most important security service in this respect is the authentication
of the entities participating in and the messages exchanged during a communication.
Strongly related to authentication is the key management whose task
it is to ensure, that the entities performing and verifying an authentication
exchange (and only they) possess the neccessary keys for this.
Our current research topics in this context are:
Security Evaluation and Design of an Authentication and Key Management
Architecture for Handover in Roaming Scenarios
Performance Issues of Authentication and Key Management
3. Experimental Testbed
|For evaluation and comparison of (selected) existing approaches and
the mechanisms developed by our group we use - besides simulation - an
experimental testbed as depicted in the following figure:
Its main components are:
a subnetwork unaware of mobility mechanisms where the corresponding host
a WAN-simulator, basically emulating the traffic- and transport-characteristics
of the Internet,
a Gateway router to the visited domain,
some routers inside the visited domain,
a cell switch, to ...,
some base stations with different technologies (IEEE 802.11, IrDA), and
some mobile hosts.
- A. Festag,
"CMAP HOW TO - A short guide to install, configure and start up
Technical Report TKN-00-004, Telecommunication Networks Group, Technische
Universität Berlin, June 2000.
- A. Neumann and
"Hierarchical Mobile IPv6 Implementation Experiences",
invited talk, IPv6 Workshop, Siemens, Munich, Germany, June 2002.
- A. Festag,
"Utilization of Multicast Mechanisms for
Gigabit Kits Workshop, St. Louis, MA,USA, July 2000.
- A. Festag,
"Rerouting for Handover in Connection-Oriented
Gigabit Kits Workshop, St. Louis, MA,USA, January 2000.
- X. Fu, C. Kappler, and H. Tschofenig,
"Analysis on RSVP Regarding Multicast",
Internet Draft, June 2002,
- R. Hancock, E. Hepworth,
C. Kappler, H. Tschofenig, J. Eisl, J. Cuellar, M. Ersue, X. Fu, H. Karl,
M. Brunner, and A. Kassler,
"Towards a Framework for QoS Signaling in the Internet",
Internet Draft, February 2002,
- X. Fu, H. Karl, A. Festag,
G. Schaefer, C. Fan, C. Kappler, and M. Schramm,
"QoS-Conditionalized Binding Update in Mobile IPv6",
Internet Draft, January 2002,
work in progress.
- A. Schrader,
H. Hartenstein, R. Schmitz, J. Quittekand, M. Momona, M. Brunner, R. Hancock,
E. Hepworth, M. Rautenberg, H. Tschofenig, C. Kappler, H.-P. Schwefel,
C. Niedermeier, H. Karl, X. Fu, and A. Kassler,
"Requirements for QoS Signaling Protocols",
Internet Draft, December 2001,
work in progress.
- H. Karl, S. Mengesha, and D. Hollos,
"Relaying in Wireless Access Networks",
Business Briefing: Wireless Technology 2002, World Markets Research Center,
London, England, January 2002.
||A. Festag, T. Assimakopoulos, L. Westerhoff,
A. Wolisz. Rerouting for Handover in Mobile Networks with Connection-Oriented
Backbones: An Experimenatal Testbed. Proceedings of the IEEE Conference
on High Performance Switching and Routing ICATM'2000, pp. 491-499, June
2000, Heidelberg, Germany
||A Festag, H. Karl, G. Schäfer. Current
Developments and Trends in Handover Design for All-IP Wireless Networks.
TKN Technical Report TKN-00-05, TU Berlin, August 2000.
||A. Festag, A. Wolisz. MOMBASA: Mobility Support
- A Multicast-based Approach. Proceedings of European Wireless 2000
together with ECRR 2000, September 2000, Dresden, Germany.
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