Showing papers by "David B. Johnson published in 1996"

Dynamic Source Routing in Ad Hoc Wireless Networks

Abstract: An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. This paper presents a protocol for routing in ad hoc networks that uses dynamic source routing. The protocol adapts quickly to routing changes when host movement is frequent, yet requires little or no overhead during periods in which hosts move less frequently. Based on results from a packet-level simulation of mobile hosts operating in an ad hoc network, the protocol performs well over a variety of environmental conditions such as host density and movement rates. For all but the highest rates of host movement simulated, the overhead of the protocol is quite low, falling to just 1% of total data packets transmitted for moderate movement rates in a network of 24 mobile hosts. In all cases, the difference in length between the routes used and the optimal route lengths is negligible, and in most cases, route lengths are on average within a factor of 1.01 of optimal.

Mobility support in IPv6

Abstract: This document specifies a protocol which allows nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node's current location. IPv6 packets addressed to a mobile node's home address are transparently routed to its care-of address. The protocol enables IPv6 nodes to cache the binding of a mobile node's home address with its care-of address, and to then send any packets destined for the mobile node directly to it at this care-of address. To support this operation, Mobile IPv6 defines a new IPv6 protocol and a new destination option. All IPv6 nodes, whether mobile or stationary can communicate with mobile nodes.

Protocols for Adaptive Wireless and Mobile Networking

Abstract: The goal of the Monarch Project1 at Carnegie Mellon University is to develop networking protocols and protocol interfaces to allow truly seamless wireless and mobile host networking. The scope of our efforts includes protocol design, implementation, performance evaluation, and usage-based validation, spanning areas ranging roughly from portions of the ISO Data Link layer (layer 2) through the Presentation layer (layer 6). In this article, we give a status report of our current work in the Monarch Project, placing it in the context of broader efforts by the Internet mobile networking community. Our work will enable mobile hosts to communicate with each other and with stationary or wired hosts, transparently making the most efficient use of the best network connectivity available to the mobile host at any time. To this end, the networking protocols must support adaptive operation in a number of ways. For example, host mobility means that protocols must be able to adapt packet routing to reach each mobile host in its current location. In addition, different wireless networks, intended for example for local-area, metropolitan-area, and wide-area use, make different tradeoffs in factors such as bandwidth, latency, error rate, and usage cost, providing different levels of quality of network connection with each wireless networking product or service. Network protocols should be able to adapt to optimize use of the best available network connection for each mobile host at any time. Further, in order to allow higher-layer protocols and applications to adapt to these changes in network connection quality, network protocols should be able to provide information to higher layers when such changes take place. We are experimenting with our protocols in the context of the “Wireless Andrew” infrastructure,currently being built at Carnegie Mellon [10]. The Wireless Andrew infrastructure builds on the current wired network infrastructure on campus, consisting mostly of 10-megabit per second Ethernet equipment. For high-speed wireless access on campus, we are installing an AT&T WaveLAN network covering most of the campus buildings [32]. WaveLAN uses direct-sequence spread spectrum radio in the 900 MHz ISM band to provide a raw data rate of 2 megabits per second. For wireless access off campus or where otherwise out of range of the WaveLAN network, we are using Cellular Digital Packet Data (CDPD) [4]. The CDPD service uses idle voice channels on the existing AMPS cellular telephone network to transmit data packets at a raw data rate of 19.2 kilobits per second.

Truly seamless wireless and mobile host networking. Protocols for adaptive wireless and mobile networking

Abstract: Describes work in routing packets to mobile hosts in a large internetwork, such as the Internet, and gives an overview of implementation work in this area. The authors discuss the problem of routing in an ad hoc network of wireless mobile hosts, as might be needed in an area without established wireless networking infrastructure; they describe a new protocol developed for routing in such a network and summarize the results from a simulation of the protocol. They then describe work in providing support for adaptive operation of higher-layer protocols and applications; they have developed an inexpensive protocol and application programming interface (API) for notifying higher layers when the quality of a mobile host's network connection changes as it moves between different locations, possibly including changes in the type of network in use at each location. Finally, they compare their work to related mobile networking research elsewhere and present conclusions.

Seamless access to multiple wireless data networks. A wireless data network infrastructure at Carnegie Mellon University

Abstract: In order to support mobile computing research, including the development of software which will allow seamless access to multiple wireless data networks, a wireless data network infrastructure is being built at Carnegie Mellon University. This infrastructure will allow researchers and other members of the campus community to use mobile computers to gain access to data networks while they are on-campus, or off-campus in the greater Pittsburgh area. The infrastructure will initially include two different types of wireless networks, a low-bandwidth wide area system and a high-bandwidth local area system, each of which will provide access to the campus computer network. Since the campus network is called "Andrew" (after Andrew Carnegie and Andrew Mellon), the new wireless infrastructure has been dubbed "Wireless Andrew". The article describes the Wireless Andrew infrastructure being built. An overview of the infrastructure and the characteristics of the two types of wireless networks used are presented. Each of these networks is then described in more detail. The technology used, its implementation in the wireless network infrastructure, and deployment experience are discussed.

Wireless Data Network Infrastructure at Carnegie Mellon University

Abstract: In order to support mobile computing research, including the development of software which will allow seamless access to multiple wireless data networks, we are building a wireless data network infrastructure at Carnegie Mellon University. This infrastructure will allow researchers and other members of the campus community to use mobile computers to gain access to data networks while they are on-campus or while they are off-campus in the greater Pittsburgh area. The infrastructure will initially include two different types of wireless networks, a low-bandwidth wide area system and a high-bandwidth local area system, each of which will provide access to our campus computer network. Since our campus network is called “Andrew” (after Andrew Carnegie and Andrew Mellon), the new wireless infrastructure has been dubbed “Wireless Andrew.” This article describes the Wireless Andrew infrastructure we are building. We begin with an overview of the infrastructure and the characteristics of the two types of wireless networks we are using. Next, we describe in more detail each of these networks. We discuss the technology used, our implementation of it in our wireless network infrastructure, and our current deployment experience. Finally, we summarize the lessons we have learned and present conclusions.

Minimizing timestamp size for completely asynchronous optimistic recovery with minimal rollback

Abstract: Basing rollback recovery on optimistic message logging and replay avoids the need for synchronization between processes during failure-free execution. Some previous research has also attempted to reduce the need for synchronization during recovery, but these protocols have suffered from three problems: not eliminating all synchronization during recovery, not minimizing rollback, or providing these properties but requiring large timestamps. This paper makes two contributions: we present a new rollback recovery protocol, based on our previous work, that provides these properties (asynchronous recovery, minimal rollback) while reducing the timestamp size; and we prove that no protocol can provide these properties and have asymptotically smaller timestamps.