procedure. This procedure provides the CN with some reasonable assurance that the MN is addressable
at its claimed care-of address and its home address.
It is generally acknowledged that there are drawbacks to route optimization. RFC 4651 presents a
taxonomy and analysis of enhancements to MIPv6 route optimization. This document notes that the
two reachability tests of the return routability procedure can lead to a handoff delay unacceptable for
many real-time or interactive applications, that the security and that the return-routability procedure
guarantees might not be sufficient for security-sensitive applications, and periodically refreshing a
registration at a correspondent node implies a hidden signaling overhead. Because of the overhead and
delay associated with the return routability procedure and because at least for ATSC it is expected that
the CN and HN will be in relative close proximity, this manual requires that IPS CNs that implement
Mobile IPv6 route optimization allow route optimization to be administratively enabled or disabled
with the default being disabled. New solutions to route optimization are expected as a result of IETF
chartered work in the Mobility Extensions for IPv6 (MEXT) working group which includes aviation-
specific requirements.
5.2 ENHANCEMENTS TO MIPV6
When a mobile node (MN) changes its point of attachment to the network, the changes may cause
delay, packet loss, and generally result in overhead traffic on the network.
5.2.1 Heirarchical Mobile IPv6 (HMIPv6)
One technology developed to address these issues is ―Heirarchical Mobile IPv6 (HMIPv6)‖ [RFC
4140]. RFC 4140 introduces extensions to Mobile IPv6 and IPv6 Neighbor Discovery to allow for
local mobility handling. HMIPv6 reduces the amount of signaling between a MN, its CNs, and its HA.
HMIPv6 introduces the concept of the Mobility Anchor Point (MAP). A MAP is essentially a local
home agent for a mobile node. A mobile node entering a MAP domain (i.e., a visited access network)
will receive Router Advertisements containing information about one or more local MAPs. The MN
can bind its current location, i.e., its On-link Care-of Address (LCoA), with an address on the MAP's
subnet, called a Regional Care-of Address (RCoA). Acting as a local HA, the MAP will receive all
packets on behalf of the mobile node it is serving and will encapsulate and forward them directly to the
mobile node's current address. If the mobile node changes its current address within a local MAP
domain (LCoA), it only needs to register the new address with the MAP. The RCoA does not change
as long as the MN moves within a MAP domain. RFC 4140 notes that the use of the MAP does not
assume that a permanent HA is present, that is, a MN need not have a permanent HoA or HA in order
to be HMIPv6-aware or use the features of HMIPv6. HMIPv6-aware mobile nodes can use their RCoA
as the source address without using a Home Address option. In this way, the RCoA can be used as an
identifier address for upper layers. Using this feature, the mobile node will be seen by the
correspondent node as a fixed node while moving within a MAP domain. This usage of the RCoA does
not have the cost of Mobile IPv6 (i.e., no bindings or home address options are sent back to the HA),
but still provides local mobility management to the mobile nodes with near-optimal routing. Although
such use of RCoA does not provide global mobility.
5.2.2 Fast Handovers for Mobile IPv6 (FMIPv6)