Showing papers by "David B. Johnson published in 1999"

The effects of on-demand behavior in routing protocols for multihop wireless ad hoc networks

Abstract: A number of different routing protocols proposed for use in multihop wireless ad hoc networks are based in whole or in part on what can be described as on-demand behavior. By on-demand behavior, we mean approaches based only on reaction to the offered traffic being handled by the routing protocol. In this paper, we analyze the use of on-demand behavior in such protocols, focusing on its effect on the routing protocol's forwarding latency, overhead cost, and route caching correctness, drawing examples from detailed simulation of the dynamic source routing (DSR) protocol. We study the protocol's behavior and the changes introduced by variations on some of the mechanisms that make up the protocol, examining which mechanisms have the greatest impact and exploring the tradeoffs that exist between them.

Supporting hierarchy and heterogeneous interfaces in multi-hop wireless ad hoc networks

Abstract: Much progress has been made toward solving the problem of routing packets inside an ad hoc network, but there are presently no complete proposals for connecting ad hoc networks together to form larger networks, or for integrating them with wired Internets. We describe a technique that allows a single ad hoc network to span across heterogeneous link layers. Using this technique, we can both integrate ad hoc networks into the hierarchical Internet and support the migration of mobile nodes from the Internet into and out of ad hoc networks via Mobile IP. Taken together, these solutions improve the scalability of flat ad hoc networks by introducing hierarchy, and they enable all nodes participating in the ad hoc network to be reachable from anywhere in the world. We have implemented each of the solutions in a real testbed of 8 nodes using the Dynamic Source Routing (DSR) protocol. Generalizing our solutions, we describe several abstract scenarios and present our ideas for solving them.

Experiences Designing and Building a Multi-Hop Wireless Ad Hoc Network Testbed

Abstract: : In this paper, we describe our experiences building a multi-hop wireless ad hoc network of 8 nodes driving around a 700 m by 300 m site. Each node runs the Dynamic Source Routing (DSR) protocol and interfaces seamlessly with existing Internet infrastructure and the Mobile IP protocol. The issues discussed in this paper range from logistical and management issues, to protocol design and performance analysis issues. We also present an early characterization of the testbed performance, and describe a significant new challenge for ad hoc network routing protocols. The major goal of the paper, however, is to share our experiences, in the belief that they may be useful to others who attempt to build other ad hoc network testbeds.

Method and apparatus for incorporating environmental information for mobile communications

Abstract: An apparatus and method for communicating between a first communication node and a second communication node in an area having a plurality of communications nodes are disclosed which comprises generating a propagation model of signals from selected communication nodes in the area. The communication nodes may be fixed or mobile. The propagation model is based on an environmental map that includes the topography of the terrain and structures in the area. The propagation model is generated at selected intervals to provide updated information for predicting the quality of communication at a location at a future time.

Method and apparatus for dynamically updating representation of a work site and a propagation model

Abstract: The present invention includes a method for dynamically updating a propagation model of communication signals in an area being subjected to earthworking operations which alter the topology of the terrain in which the method comprises the steps of dynamically updating a terrain map of the area as a function of the earthworking operations and dynamically updating the propagation model in response to updating the terrain map. An apparatus for dynamically updating a propagation model of communication signals in an area being subjected to a mobile geography-altering machine capable of altering the topology of the terrain, the apparatus comprises circuitry for storing a terrain map representative of the terrain prior to the terrain being subjected to alteration by the mobile geography-altering machine, circuitry for dynamically updating the terrain map as the terrain is being subjected to alteration by the mobile geography-altering machine, and circuitry for dynamically updating the propagation model in response to updating the terrain map.

Reserved IPv6 Subnet Anycast Addresses

Abstract: The IP Version 6 addressing architecture defines an "anycast" address as an IPv6 address that is assigned to one or more network interfaces (typically belonging to different nodes), with the property that a packet sent to an anycast address is routed to the "nearest" interface having that address, according to the routing protocols' measure of distance. This document defines a set of reserved anycast addresses within each subnet prefix, and lists the initial allocation of these reserved subnet anycast addresses.

Emulation of Ad Hoc Networks

Abstract: Stress testing of networking code via macfilter  Used to debug our 8 node ad hoc network testbed  Description of interesting/problematic movement scenarios created  Changing network topology extracted into trace file  Physical machines running actual implementation synchronously read trace-file  Machines prevented from receiving packets from non-neighbors  Described at previous IETF and in CMU CS Tech Report 99-116