The customary Internet protocol (IP) mandates changing IP addresses for communicating mobile devices in motion over different networks. Contrarily, with mobile IP, home agents (HAs) transmit packets to mobile node destinations without modifying IP addresses. Unfortunately, any failure in a single HA managing mobile nodes will disrupt the delivery of packets. The design of fault-tolerant HAs creates fanciful research questions. How should an algorithm for coping with failures of simultaneous multiple mobile agents (MMAs) of a home network be designed? How might unreliable network control signals and irrecoverable volatile media data of a disrupted mobile agent be reconciled?

There are algorithms for resolving the issues of efficiency, fault-tolerant robustness, and load balancing in MMAs [1,2]. However, the existing MMA protocols require each HA to maintain the mobility bindings of all registered mobile nodes (MNs) in the home network. Moreover, the synchronization process of mobility bindings among HAs via forwarding of registration requests is time consuming, particularly with a large number of MNs in frequent motion. Consequently, Huang and Chuang present an efficient fault-tolerant MMA protocol with only double mobility bindings for coping with failures in HAs. In the protocol, each physical HA uses a table of logical HAs and backup locations, and a table of backup HAs for taking over control in the event of failures. Timed message advertisements are used to detect communication failures, registration requests received from MNs are forwarded for synchronizing the mobility binding of a logical HA and its backup, and accumulated mobility bindings are restored by a selected physical HA in a recovery mode. All active physical HAs with sufficient memories serve as candidate backups depending on the workloads in the home network.

The authors used five generators in simulation experiments to generate and submit different packet types at alternative processing costs and flow paths to waiting queues of MAs in a home network. The new MMA protocol exhibited lower registration delays, forwarding overheads, and sensitivity to MN mobility than the well-known fault-tolerant mobile IP. The novel protocol also displayed higher fault tolerance and lower takeover time than the familiar stable storage approach. Accordingly, the new MMA protocol is a viable fault-tolerant protocol for mobile IP.