Wireless Future - Telenor

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Domain
GFA/MAP
Figure 3-3 Architecture of
a multiple care of address
scheme
Internet
Border
Router
Router Router Router
FA FA FA
need to maintain a forwarding entry for all active
nodes. It also means that table look-up becomes
a demanding task in terms of processing. These
schemes may thus present scalability problems
as the network grows and the number of active
nodes increases. Furthermore operation assumes
a tree-like structure since the gateway is a single
entry point into the cellular IP domain. Reliability
and performance are thus also a concern.
3.3 Multiple Care-of Addresses
3.3.1 Principles
There are several proposals that follow the multiple
care-of address approach. Among others,
Mobile Regional Registration and Hierarchical
Mobile IP (for IPv6) have gained considerable
attention in IETF. All these proposals allow the
domain to have any arbitrary topology. The
architecture (Figure 3-3) typically consists of
subnet-level agents, which essentially provide
an MH with a local COA (LCOA). This COA
identifies the MH’s current subnet of attachment.
A separate agent, the GFA (Global Foreign
Agent) or MAP (Mobility Anchor Point)
resides at a higher level in the domain hierarchy
and provides the MH with a stable point of
attachment. This point of attachment remains the
same while the MH is in the same domain. The
global care-of address either refers to an address
associated with the top-level agent or an address
for which packets are intercepted by the agent.
Since only the global COA is available to a CH
located outside the domain, all packets destined
to the MH use this COA. The MA/GFA intercepts
these packets and then forwards them to
the MH’s local COA.
Having previously focused on IPv4, we thought
it adequate to present a scheme designed primarily
for IPv6, so we only present Hierarchical
Mobile IPv6 in this chapter.
3.3.2 Hierarchical Mobile IPv6
In this scheme [6] the MH discovers the address
of the MAP through router advertisements. The
MH registers with the MAP using its local careof
address and permanent home address. Then
it sends binding updates to the CH and the HA
indicating the MAP’s address as the alternative
care-of address (ACOA). The CH can then transmit
packets using the routing header option
directly to this ACOA. The MAP will then forward
the packet towards the Local CoA
(LCOA).
On subsequent movement within the domain, the
MH obtains a new Local COA (based on the
stateless autoconfiguration mechanism) and then
updates its MAP of this new LCOA. The MAP
can then tunnel packets to this new LCOA.
The domain of a MAP is defined as the area
where the router advertisement is advertising
the identity of the MAP. Thus movement across
domains is detected when the MAP address in
the router advertisement has changed. When the
MH has moved into a new domain, it sends the
address of the new MAP (ACOA) in separate
BUs to each of its CHs and its HA.
The MH must also check for the existence of
a routing header in the inner packet; if such a
header exists, the MH can assume that the CH is
aware of its ACOA and does not need to receive
a new BU.
3.3.3 Analysis
The main benefit of a scheme like HMIPv6 is of
course the reduced global signalling compared to
Mobile IPv6. It also enables the use of standard
IP routers in each domain thus avoiding the cost
of manufacturing special routers. The main
drawback is that tunnelling is required inside the
domain (between the MAP and the MH) which
results in
• Poor transport efficiency;
• High Header processing complexity in the
MH and Intermediate foreign agents.
Telektronikk 1.2001