Wireless Future - Telenor

mechanisms allow a handoff of a mobile node
from one cell to another, re-establishing linklayer
connectivity to the node in each new location.
Within the natural limitations imposed by
link-management solutions, and as long as such
handoff occurs only within cells of the mobile
node’s home link, such link-layer mobility
mechanisms may offer faster convergence and
lower overhead than Mobile IPv6. Extensions to
the Mobile IPv6 protocol have been proposed to
support a more local, hierarchical form of mobility
management.
3 Micro-mobility and Fast
Handoff
3.1 Background
The design of Mobile IP is based on the assumption
that the rate of movement between subnets
is low. This leads to the fact that the protocol is
not suited for micro-mobility support for which
the change of IP subnet is assumed to be frequent.
More specifically, the registration process
requires that a new registration is sent to the
Home Agent for every change of subnet. This
registration process induces unnecessary high
signalling load on the global Internet and high
processing needs in the Home Agents. It also
leads to unnecessary latency during handoff
from one subnet to another.
Several schemes have been proposed to solve
the issue of micro-mobility management. All of
these proposals assume a hierarchy in order to
localise the scope of the mobility management to
a domain (collection of subnet administrated by
a single provider). Doing so reduces the global
signalling traffic and enables a lower latency
period during a change of subnet. These proposals
assume Mobile IP for inter domain mobility
and mainly focus on the intra domain mobility.
There are two main concepts for managing the
intra-domain mobility:
The Host-based routing approach: Mobility
management is distributed among all the nodes
within the domain. Host-specific routing is
employed to keep track of the current location of
the Mobile Host (MH) within the domain. Special
routers are thus needed. The address of the
user is the care-of address assigned/authorised
by the domain.
The multiple Care-of Address approach: The
Mobile Host is assigned multiple care-of
addresses (COA), with each address identifying
a specific agent/node in the hierarchy. Packets
are routed through each node in the hierarchy
using the corresponding care-of address. The
Mobile Host only changes the care-of address of
the lowest hierarchical level at every change of
subnet. This approach uses conventional IP rout-
Telektronikk 1.2001
ing in the domain and distributes the mobility
management over only a subset of nodes in the
mobility domain.
In the following we present these two concepts
in more detail. We also review some of the proposed
schemes and analyse their strong points
and deficiencies. We note that at this point in
time the schemes presented are in the form of
Internet drafts and are thus under discussion in
the IETF.
3.2 Host based Routing Schemes
3.2.1 Principles
Many schemes belonging to the host based routing
category have been proposed. The Cellular
IP and Hawaii schemes have received most of
the attention thus far. Figure 3-1 illustrates the
basic functional architecture and the implied tree
like network topology of the Hawaii and Cellular
IP solutions. Both approaches create hostspecific
entries through a specific path in the
network topology. The ingress point into the
domain is the root of the tree and is called the
Gateway (GW) for Cellular IP and Domain Root
Router (DRR) for the Hawaii scheme. Packets
destined to the MH are forwarded through the
sequence of nodes, the first one being the ingress
point and the last one being the MH. It should be
noticed that the edge device may not be a base
station so that the schemes are applicable to
solving mobility management in fix access networks
as well. As an MH moves inside this
Cellular IP/Hawaii
Domain
Internet
GW/DRR
Router* Router*
Figure 3-1 Cellular IP
and Hawaii architecture
Router* Router* Router* Router*
MH
* Router with CIP or Hawaii Protocol
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