Problems with Mobile IP and Their Solutions

Mobile IP, the outcome of the convergence of mobile communication technologies and the IP network, is the core technology to implement NGN applications in traditional networks. It supports network mobility, two-way access, and real-time multimedia services.

As a recommended Internet standard, Mobile IP is the earliest solution to mobility management of IP network. The IETF (Internet Engineering Task Force) gives a complete description of Mobile IP in RFC2002. Along with the development of IPv4 to IPv6, Mobile IP is also evolving to Mobile IPv6.

Problems with Mobile IP:

Although growing rapidly, Mobile IP still has the following problems:

(1) "Triangle routing" Problem

The Communication Host (CH) has to send packets to the Mobile Host (MH) via the Home Agent (HA), while the MH sends packets directly to the CH. As the communication in the two directions follows different routes, the problem of "triangle routing" arises, which leads to low efficiency especially when the MH is far away from the HA and the CH is near to the MH.

(2) Handoff Problem

Handoff problem means that the HA sends the IP packets of the MH to the original foreign network via the tunnel because it doesn’t know the latest Care of Address (CoA) of the MH during the period starting when the MH leaves the original foreign network and ending when the HA receives the new registration address of the MH. As a result, these dropped IP packets have an influence on the communication between the MH and the CH especially when handoff occurs frequently or the MH is far away from the HA.

(3) Problem of Intra-Domain Movement

The frequent intra-domain movement of the MH within a small area will lead to frequent handoff. Consequently, a great amount of registered messages are generated in the network and the network performance is greatly affected.

(4) QoS Problem

In the mobile environment, it is hard to provide QoS over Mobile IP due to dynamically varying wireless network topologies, limited network resources, unpredictable effective bandwidth and high error rate.

Solutions:

Solution to "Triangle Routing" Problem For Mobile IP, routing optimization is necessary because all packets sent to the MH shall pass through the HA but the route may not be the best. After receiving the packets sent by the CH to the MH, the HA notifies the CH of the binding information about the MH, i.e., the current Foreign Agent (FA) address of the MH, and the CH encapsulates the packets and establishes the tunnel to the FA for transparent transmission. The binding information is transferred via a definite port number. If the MH moves again, the new FA will transfer the updated binding information to the old FA to ensure that the packets are transferred to the new FA. And meanwhile the HA gets the updated binding information so the subsequent packets will be transferred directly from the CH to the new FA. The mobile IP with route optimization sets high requirements on the CH. The CH shall have the ability to obtain the binding information, encapsulate the packets and establish the tunnel. Therefore the CH protocol stack needs lots of modifications.

Alcatel-Lucent Wireless IP solutions: Wireless All Around: