Enhancements to IPv6 Mobility Management Protocols Required by 4G Networks

Although the features mentioned are suited for 4G networks, recently, there has been almost universal recognition that IPv6 needs to be enhanced to meet the need for future 4G cellular environments. In particular, the absence of a location management hierarchy (IPv6 uses only simple location updates for location management) leads to concerns about the signalling scalability and handoff latency. This is especially significant when we consider that 4G aims at providing mobility support to potentially billions of mobile devices, within the stringent performance bounds associated with real time multimedia traffic.

There are three main areas where IPv6 needs to be enhanced before being used as the core networking protocol in 4G networks:

1. Paging Support: The base IPv6 specification does not provide any form of paging support. Hence to maintain connectivity with the backbone infrastructure, the mobile node needs to generate location updates every time it changes its point of attachment, even if it is currently in dormant or standby mode. Excessive signaling caused by frequent motion leads to a significant wastage of the mobile node's battery power, especially in environments with smaller cell areas (such as 802.11 based cellular topologies). It is thus impractical to rely completely on location updates and is essential to define some sort of flexible paging support in the intra-domain mobility management scheme.
2. Scalability: IPv6 allows nodes to move within the Internet topology while maintaining reachability and on-going connections between mobile and correspondent nodes. To do this a mobile node (MN) sends Binding Updates (BUs) to its Home Agent (HA) and all Correspondent Nodes (CNs) it communicates with, every time it moves. Authenticating binding updates requires approximately 1.5 round trip times between the mobile node and each correspondent node (for the entire return routability procedure in a best case scenario, i.e. no packet losses). In addition one round trip time is needed to update the HA; this can be done simultaneously while updating CNs. These round trip delays will disrupt active connections every time a handoff to a new radio access technology is performed. Elimination of this additional delay element from the time-critical handover period will significantly improve the performance of IPv6. Moreover, in the case of wireless links, such a solution reduces the number of messages sent over the air interface to all CNs and the HA. A local anchor point will allow Mobile IPv6 to benefit from reduced mobility signaling with external networks. For these reasons a new Mobile IPv6 node, called the Mobility Anchor Point (MAP) is being suggested, that can be located at any level in a hierarchical network of routers. Unlike Foreign Agents in IPv4, a MAP is not required on each subnet. The MAP will limit the amount of Mobile IPv6 signaling outside the local domain. The introduction of the MAP provides a solution to the aforementioned problems in the following way:
   1. The MN sends binding updates to the local MAP rather than the HA (which is typically further away) and CNs.
   2. Only one binding update message needs to be transmitted by the MN before traffic from the HA and all CNs is re-routed to its new location. This is independent of the number of CNs that the MN is communicating with. Thus by decreasing signaling traffic by having an intermediate level in the hierarchy helps accommodate a larger number of mobile nodes in the system.
3. Technologies: A mobile node switches from one network to another network in one of two cases: (a) when the signal from the network it is currently in starts to become weak or (b) when the mobile host detects another network which is better suited to its application compared to its current network.

The decision of the mobile device on the suitability of the network can be based on signal strength, network bandwidth or certain policies which the user might have stored in his profile based on which subsequent switching between networks of different access technologies may occur. For example, when a user is streaming a video, he/she may use WLAN and when he/she is listening to highly compressed audio, she might switch to GPRS.

Further, another issue that needs to be resolved is that of informing the source (HA/CN) when the MN has moved. In such a situation, the MN does a location update to its HA, which then takes charge of sending IP datagrams to the MN's new location using standard Mobile-IP mechanisms.

In line with the 4G vision of bringing together wide-area networks and local-area packet-based technologies, mobile terminals are being designed with multiple physical or software-defined interfaces. This is expected to allow users to seamlessly switch between different access technologies, often, with overlapping areas of coverage and dramatically different cell sizes. Mobility management protocols should then be capable of handling vertical handoffs.