Browsing by Author "Bhagwat, Pravin"
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Item A framework for integrating Mobile Hosts within the Internet(1998-10-15) Bhagwat, PravinHost mobility and wireless access are two emerging design considerations that pose challenging problems at all layers of the networking protocol stack. This dissertation investigates their impact on the design of link, network, and transport layer protocols. At the network layer, we have designed and implemented a new routing architecture that allows the current set of Internet standards to support routing to mobile hosts. At the link and transport layers, we have designed mechanisms to improve throughput over error-prone wireless channels. At the network layer, the most crucial problem is that of routing. The existing Internet routing mechanisms cannot route packets to hosts whose points of attachment to the network change over time. Exploiting IP's Loose Source Route option, we have designed and implemented a routing scheme which provides location independent network access to TCP/IP compliant mobile hosts. It also allows mobile hosts equipped with multiple network interfaces to dynamically migrate active network sessions from one network interface to another. The proposed scheme only requires the addition of two new entity types, Mobile Routers and Mobile Access Stations. These entities perform all required mobility-aware functions, such as address translation, user tracking and location management. No modifications to existing host or router software are required. Although MobileIP provides continuous network connectivity to mobile hosts, the effects of host movement and wireless medium characteristics are often visible at the transport layer. We consider the effect of wireless medium characteristics on the performance of Transmission Control Protocol (TCP) sessions. Unlike wired networks, packets transmitted on wireless channels are often subject to burst errors which cause back to back packet losses. We show that TCP's error-recovery mechanisms perform poorly when packets from a TCP session are subject to burst errors. Unlike other approaches which require modification to TCP, our solution requires enhancements only at the wireless link layer, thus making it applicable to other transport protocols as well. We use a Channel State Dependent Packet (CSDP) scheduler which takes wireless channel characteristics into consideration in making packet dispatching decisions. Our results show that the CSDP technique provides improved throughput, better channel utilization, and fairness among multiple TCP streams. (Also cross-referenced as UMIACS-TR-95-124)Item Network Layer Mobility: an Architecture and Survey(1998-10-15) Bhagwat, Pravin; Tripathi, Satish K.; Perkins, CharlesIn this paper we explore various network layer concepts that pertain to the design of mobile networking systems. We show that mobility is essentially an {\em address translation} problem and is best resolved at the network layer. We have identified the fundamental services that must be supported at the network layer to carry out the task of address translation. Using these service primitives as building blocks, we propose a network layer architecture which enables smooth integration of mobile end systems within the existing Internet. The architecture is modularized into well-defined logical components. In this paper our objective is not to propose {\em a specific scheme} for supporting mobility, rather it is to highlight and analyze the essential aspects of supporting mobile end-systems, as well as to better understand the trade-off between various design alternatives. (Also cross-referenced as UMIACS-TR-95-117)Item Proximity Awareness and Ad Hoc Network Establishment in Bluetooth(2001) Salonidis, Theodoros; Bhagwat, Pravin; Tassiulas, Leandros; LaMaire, Richard; ISRIn recent years, wireless ad hoc networks have been a growing area of research. While there has been considerable research on the topic of routing in such networks, the topic of topology creation has not received due attention. This is because almost all ad hoc networks to date have been built on top of a single channel, broadcast-based wireless media, suchas 802.11 or IR LANs. For such networks the distance relationship between the nodes implicitly (and uniquely) determines the topology of the ad hoc network.Bluetooth is a promising new wireless technology that enables portable devices to form short-range wireless ad hoc networks and is based on a frequency hopping physical layer. This fact implies that hosts are not able to communicate unless they have previously discovered each other by synchronizing their frequency hopping patterns. Thus, even if all nodes are within direct communication range of each other, only those nodes which are synchronized with the transmitter can hear the transmission.
To support any-to-any communication, nodes must be synchronized so that the pairs of nodes (which can communicate with each other) together form a connected graph.
Using Bluetooth as an example, this paper first provides deeper insights into the issue to link establishment in frequency hopping wireless systems. It then introduces the Bluetooth Topology Costruction Protocol (BTCP), an asynchronous distributed protocol for constructing scatternets which starts with nodes that have no knowledge of their surroundings and terminates with the formation of a connected network satisfying all connectivity constraints posed by the Bluetooth technology.
To the best of our knowledge, the work presented in this paper is the first attempt at building Bluetooth scatternets using distributed logic and is quite "practical" in the sense that it can be implemented using the communication primitives offered by the Bluetooth 1.0 specifications.