Although Mobile IPv6 is a powerful Internet mobility protocol, it presents some weaknesses for frequently migrating hosts. Specifically, after each host migration, a local temporary address must be obtained and communicated to a possibly distant Home Agent.
This significantly disturbs TCP connections while causing network signaling overload. The simplest way to alleviate this weakness is to introduce hierarchies into the IP mobility infrastructure. A hierarchical IP mobility management scheme specifies that host mobility should be handled where it originates, namely in the access network.
Cellular IPv6 is such an approach, which combines the efficiency and scalability of IP with inherent features found in cellular networks, such as seamless handoff support, passive connectivity and paging.
Thus, Cellular IPv6 is a Mobile IPv6 protocol extension and not a replacement. A Cellular IPv6 network is comprised of a Gateway router that connects the network to the Internet as well as a set of nodes that are responsible for routing packets to Mobile Hosts connected to the network via wireless access points called Base Stations.
The Cellular IPv6 desing and implementation is based on the original implementation of the Columbia University. The main design issues for Cellular IPv6 are:
Mobile-IPv6-capable hosts, use their IPv6 care-of address as the source of every packet they send and carry their permanent Home IPv6 address into a Home address destination options header. In order to be in line with Mobile IPv6 specification, the Cellular IPv6 control packets (route-updates and paging-updates) are sent uplink with source address the Mobile Host's IPv6 care-of address.
On the reverse direction, IPv6 packets destined to a Mobile Host reach the Cellular IPv6 Gateway in two alternative structures:
This means that the sender is not aware of the recipient Mobile host's current care-of address, and sends the packet with destination its Home IPv6 address.
This packet is normally routed to the Mobile Host's Home Network, where it is intercepted by the local Home Agent which next encapsulates and sends the packet to the Mobile host's current care-of address.
This means that the sender has a fresh binding for the recipient Mobile Host and sends the packet directly to its current care-of address. In this case, the sender maps the Mobile Host's Home IPv6 address as the last entry in the routing header, while the Mobile Host's current care-of address is mapped as second-to-last.
Packets addressed to a Mobile Host will be routed towards the Cellular IPv6 Gateway/Router using prefix-based routing. Next, Cellular IPv6 host-based routing into the Cellular IPv6 Access Network will forward packets to the Mobile Host, through the Base Station that it is currently attached to.
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