Multiplex communications – Network configuration determination
Reexamination Certificate
1998-08-24
2001-10-16
Patel, Ajit (Department: 2662)
Multiplex communications
Network configuration determination
C370S238000, C370S351000, C370S338000
Reexamination Certificate
active
06304556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to two network protocols which are particularly suitable for self-reconfigurable communications networks, such as ad-hoc networks. More particularly, the first protocol is instrumental in efficiently finding routes within a network, while the second protocol can be used to locate users in a network with rapidly changing topology.
2. Background Information and Description of the Prior Art
A. The Notion of the Ad-Hoc Network
An ad-hoc network architecture is a network that can be deployed rapidly and without relying on preexising fixed network infrastructure. The nodes in an ad-hoc network can dynamically join and leave the network, frequently, often without warning, and without disruption to other nodes' communication. Finally, the nodes in the network can be highly mobile, thus rapidly changing the node constellation and the presence or absence of links. Examples of the use of the ad-hoc networks are:
tactical operation—for fast establishment of communication infrastructure during force deployment in unknown and hostile terrain;
rescue missions—for communication in areas without adequate wireless coverage;
national security—for communication in times of national crisis, where the existing communication infrastructure is non-operational due to a natural disaster or a global war;
law enforcement—for fast establishment of communication infrastructure during law enforcement operations;
commercial use—for setting up communication in exhibitions, conferences, or sale presentations;
education—for operation of wall-free (virtual) classrooms; and
sensor networks—for communication between intelligent sensors (e.g., MEMS) mounted on mobile platforms.
Nodes in an ad-hoc network exhibit nomadic behavior by freely migrating within some area, and dynamically creating and tearing down associations with other nodes. Groups of nodes that have a common goal can create formations (clusters) and migrate together, similarly to military units on missions. Nodes can communicate with each other at anytime and without restrictions, except for connectivity limitations and subject to security provisions. For example, in military applications, the network nodes can represent soldiers, trucks, tanks, planes helicopters, ships or unmanned robots.
Some of the distinctive attributes of ad-hoc networks are:
the network should be immediately deployable (and re-deployable) in unknown, arbitrary communication environments;
radio propagation conditions can differ vastly throughout the network coverage and can constantly change;
connectivity between adjacent nodes can be intermittent and sporadic, both due to the nodal mobility and due to propagation conditions; and
there may not be any fixed infrastructure present; the mobile nodes are all the elements of the network.
B. The Challenges of the Ad-Hoc Networks and Previous Work
The topic of ad-hoc networking has received increased attention recently. This interest comes from two different directions—from the military and from the Internet community. Of course, as the communication and networking environment of these two “markets” is quite different, the requirements, and more important the expectations, of what this technology can accomplish are quite different as well.
The three main challenges in the design and operation of the ad-hoc networks stem from
the lack of a centralized entity;
the possibility of rapid platform movements; and
the fact that all communication is carried over the wireless medium.
In “regular” cellular wireless networks, there are a number of centralized entities; e.g., the base stations, the Mobile Switching Centers (MSC-s), and the Home Location Registry. In ad-hoc networks, since there is no preexisting infrastructure, these centralized entities do not exist. The centralized entities in the cellular networks perform the function of coordination. Thus, lack of these entities in the ad-hoc networks requires more sophisticated distributed algorithms to perform these functions. In particular, the traditional algorithms for mobility management, which rely on the HLR/VLR (Home Location Register/Visitor Location Register) and the medium access control schemes, including the channel assignment procedures, which rely on the base-station/MSC (Mobile Switching Center) support, cannot be used here.
All communications between all network entities are carried in ad-hoc networks over the wireless medium Of course, due to the radio communications being extremely vulnerable to propagation impairments, connectivity between network nodes is not guaranteed. In fact intermittent and sporadic connectivity may be quite common. Additionally, as the wireless bandwidth is limited, its use should be minimized. Finally, as some of the mobile devices are expected to be hand-held with limited power sources, the required transmission power should be minimized as well The last two attributes, conservation of wireless spectrum and reduction in transmission power, lead naturally to an architecture in which the transmission radius of each mobile is limited and channels assigned to mobiles are spatially reused. Consequently, since the transmission radius is much smaller than the network span, communication between two terminals may need to be relayed through intermediate nodes; i.e., multi-hop routing.
Because of the possibly rapid movement of the nodes and fast changing propagation conditions, network information, such as routing, for example, becomes quickly obsolete. This leads to frequent network reconfiguration and frequent exchanges of control information over the wireless medium. Of course, as the wireless spectrum is at premium, frequent exchanges of large amounts of data over the air should to be avoided. Moreover, because of the fast changing topology, a large portion of the reconfiguration information will never even be used. Thus, the bandwidth used for distribution of the routing update information is wasted. Finally, in spite of these attributes, the design of the ad-hoc networks still needs to allow for a high degree of reliability, survivability, availability and manageability of the network.
Based on the above discussion, the following features are considered as highly desirable for the successful operating of ad-hoc networks:
Robust routing and mobility management algorithms to increase the networks reliability, survivability and availability; i.e., any remaining network components should operate even in the case that a large portion of the network is wiped out, partitioned, or incapacitated;
Adaptive algorithms and protocols to adjust to frequently changing radio propagation, network, and traffic conditions;
Low-overhead algorithms and protocols to preserve the radio communication resource;
Multiple (distinct) routes between a source and a destination—to reduce the congestion in the vicinity of certain nodes, and to increase the reliability and survivability; and
Non-hierarchical physical network architecture to avoid the susceptibility to network failures, congestion around certain nodes, and the penalty due to inefficient routing.
Routing Protocols
The routing protocols published in the literature are inadequate for the ad-hoc network communications environment. More specifically, the challenges stem from the fact that, on one hand, in-order to determine a packet route, at least the reachable information of the source's neighbors needs to be known to the source node. On the other hand, in an ad-hoc network, this topology may change quite often. Furthermore, as the number of network nodes can be large, the potential number of destinations is also large, requiring large and frequent exchange of data (e.g., routes, routes updates, or routing tables) among the network nodes. Thus, the amount of update traffic is quite high. This is in contradiction with the fact that updates are expensive in the wireless communication environment.
The existing routing protocols can be classified either as proactive or as reactive. Proactive protocols attempt to continuou
Cornell Research Foundation Inc.
Jones, Tullar & Cooper
Patel Ajit
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