Investigation into Mobile
Routing for Use with
Inclusive Dates: 07/01/00 - 11/31/00
Background - The Intelligent Transportation System (ITS) networks developed for regional Departments of Transportation (DOTs) are becoming increasingly more complex and are often not compatible. Interoperability between cities and states is emerging as an important component in future and current ITS network designs. Included with this interoperability are the desires to use developed roadside networks for multiple applications and to extend the benefits of ITS, such as specialized emergency services, into rural areas. To achieve rural connectivity for ITS applications, alternative means of network connectivity, such as satellites, must be used. A great need exists to couple the differing ITS infrastructures and system connectivities without increasing the complexity of operating the mobile end devices. The mobile routing technology investigated during this research effort allows for this level of system connectivity and coupling.
Approach - Mobile routing is an implementation and extension of the mobile internet protocol (IP) communications standard. Mobile IP allows an end device to maintain a specified IP address for network connectivity while moving between different "foreign" networks by assigning it a care-of address that changes at each foreign connection. This mobile end device connects to the foreign networks via foreign agent (FA) routers. Data sent to the mobile end device from its home network passes through a home agent (HA), which forwards it to the mobile end device's new IP address (care-of address) using a scheme called tunneling. This procedure occurs transparently to the user; no modifications to the IP address of the mobile end device are required. The mobile routing technology provides for an entire subnet of the home network to roam using only one mobile IP interface and provides for a preference-based decision process when multiple networks are available for connection at any given time.
The test network developed for this research incorporates a satellite connection to supplement a roadside spread-spectrum infrastructure. The satellite link provides roaming capabilities within the wireless ITS infrastructure and in remote areas. This test network can establish a tunnel between the home network and the mobile network using either of the communication interfaces through their associated FAs. This scenario is tested with a firewall securing the home network to ensure the data path can be adequately secured.
Accomplishments - System performance using the mobile routing is critical because many ITS applications require large bandwidths with little latency. A test scenario is created to emulate a real-time videoconference from a vehicle traveling between two cities. During the test scenario, the vehicle communicates to a terrestrial wireless infrastructure in "City 1," switches to a satellite link for rural connectivity, and finally switches to the terrestrial wireless infrastructure of "City 2" when it becomes available. During this test scenario, the terrestrial wireless communications links are preferred over the satellite link because they allow for a much larger data throughput. Mobile routing provides for a seamless transition between the differing networks using its inherent 'preferred-path' capabilities. There is a slight performance penalty for using the mobile routing technology in both system latency and data throughput. These issues were most noted during the transitions between networks.