Nicholas F. Maxemchuk

Reliable broadcast protocols

A broadcast protocol system which uses a plurality of distributed computers which are electrically connected by a broadcast medium. Each message is broadcast to all computers with a header in which there is a message identifier containing the identity of the broadcasting processor and a message sequence number. A retransmission number is also included in the identifier to distinguish retransmissions. Each processor maintains an acknowledgement list of message identifiers with positive and negative acknowledgements.

Routing in the Manhattan Street Network

The Manhattan Street Network is a regular, two-connected network, designed for packet communications in a local or metropolitan area. It operates as a slotted system, similar to conventional loop networks. Unlike loop networks, routing decisions must be made at every node in this network. In this paper, several distributed routing rules are investigated that take advantage of the regular structure of the network. In an operational network, irregularities occur in the structure because of the addressing mechanisms, adding single nodes, and failures. A fractional addressing scheme is described that makes it possible to add new rows or columns to the network without changing the addresses of existing nodes. A technique is described for adding one node at a time to the network, while changing only two existing links. Finally, two procedures are described that allow the network to adapt to node or link failures. The effect that irregularities have on routing mechanisms designed for a regular structure is investigated.

A survey of inter-vehicle communication protocols and their applications

Inter-vehicle communication (IVC) protocols have the potential to increase the safety, efficiency, and convenience of transportation systems involving planes, trains, automobiles, and robots. The applications targeted include peer-to-peer networks for web surfing, coordinated braking, runway incursion prevention, adaptive traffic control, vehicle formations, and many others. The diversity of the applications and their potential communication protocols has challenged a systematic literature survey. We apply a classification technique to IVC applications to provide a taxonomy for detailed study of their communication requirements. The applications are divided into type classes which share common communication organization and performance requirements. IVC protocols are surveyed separately and their fundamental characteristics are revealed. The protocol characteristics are then used to determine the relevance of specific protocols to specific types of IVC applications.

Copyright protection for the electronic distribution of text documents

Each copy of a text document can be made different in a nearly invisible way by repositioning or modifying the appearance of different elements of text, i.e., lines, words, or characters. A unique copy can be registered with its recipient, so that subsequent unauthorized copies that are retrieved can be traced back to the original owner. In this paper we describe and compare several mechanisms for marking documents and several other mechanisms for decoding the marks after documents have been subjected to common types of distortion. The marks are intended to protect documents of limited value that are owned by individuals who would rather possess a legal than an illegal copy if they can be distinguished. We describe attacks that remove the marks and countermeasures to those attacks. An architecture is described for distributing a large number of copies without burdening the publisher with creating and transmitting the unique documents. The architecture also allows the publisher to determine the identity of a recipient who has illegally redistributed the document, without compromising the privacy of individuals who are not operating illegally. Two experimental systems are described. One was used to distribute an issue of the IEEE Journal on Selected Areas in Communications, and the second was used to mark copies of company private memoranda.

Electronic marking and identification techniques to discourage document copying

Modern computer networks make it possible to distribute documents quickly and economically by electronic means rather than by conventional paper means. However, the widespread adoption of electronic distribution of copyrighted material is currently impeded by the ease of unauthorized copying and dissemination. In this paper we propose techniques that discourage unauthorized distribution by embedding each document with a unique codeword. Our encoding techniques are indiscernible by readers, yet enable us to identify the sanctioned recipient of a document by examination of a recovered document. We propose three coding methods, describe one in detail, and present experimental results showing that our identification techniques are highly reliable, even after documents have been photocopied. >

Copyright protection for electronic publishing over computer networks

One of the major challenges faced by electronic publishing is that of preventing individuals from easily copying and illegally distributing electronic documents. The authors explore the use of cryptographic protocols to discourage the distribution of illicit electronic copies, and propose an architecture and two separate strategies for making electronic document distribution secure. >

Document marking and identification using both line and word shifting

Continues a study of document marking to deter illicit dissemination. An experiment performed reveals that the distortion on the photocopy of a document is very different in the vertical and horizontal directions. This leads to the strategy that marks a text line both vertically using line shifting and horizontally using word shifting. A line that is marked is always accompanied by two unmarked control lines one above and one below. They are used to measure distortions in the vertical and horizontal directions in order to decide whether line or word shift should be detected. Line shifts are detected using a centroid method that bases its decision on the relative distance of line centroids. Word shifts are detected using a correlation method that treats a profile as a waveform and decides whether it originated from a waveform whose middle block has been shifted left or right. The maximum likelihood detectors for both methods are given.

Comparison of deflection and store-and-forward techniques in the Manhattan Street and Shuffle-Exchange Networks

The Manhattan Street Network (MS-Net) and Shuffle-Exchange Network (SX-Net) are two-connected networks with significantly different topologies. Fixed-size packets are transmitted between nodes in these networks. The nodes are synchronized so that all of the packets that are received by a node within a slot transmission time arrive at a switching point simultaneously. Instead of storing large numbers of packets at intermediate nodes, a deflection strategy similar to hot-potato routing is used. There are characteristics of the MS-Net that make it well suited for deflection routing. With no buffer, 55-70% of the throughput with an infinite number of buffers has been obtained; with a single buffer per node, the throughput increases to 80-90%. With uniform load the throughput does not decrease significantly as the network utilization increases. Therefore, additional flow control mechanisms are not required to achieve the highest network throughput. The SX-Net does not have the above characteristics of the MS-Net. However, deflection routing still provides a significant portion of the available throughput. In the SX-Net, more buffers are required than in the MS-Net, and a flow control mechanism must be used to achieve the greatest throughput.<<ETX>>

Improving the fairness of distributed-queue-dual-bus networks

The fairness problems suffered by distributed-queue-dual-bus (DQDB) networks that span metropolitan areas are examined in detail. The problems arise because the network control information is subject to propagation delays that are much longer than the transmission time of a data segment. A rate control procedure is proposed that requires only a minor modification of the current DQDB protocol. In order to guarantee that a node acquires only 90% of the available slots, every time it inserts nine data segments into its local queue it inserts one extra request slot into its transmission queue. This lets an extra idle slot go by that was not requested by any downstream node.<<ETX>>

Document identification for copyright protection using centroid detection

A way to discourage illicit reproduction of copyrighted or sensitive documents is to watermark each copy before distribution. A unique mark is embedded in the text whose recipient is registered. The mark can be extracted from a possibly noisy illicit copy, identifying the registered recipient. Most image marking techniques are vulnerable to binarization attack and, hence, not suitable for text marking. We propose a different approach where a text document is marked by shifting certain text lines slightly up or down or words slightly left or right from their original positions. The shifting pattern constitutes the mark and is different on different copies. In this paper we develop and evaluate a method to detect such minute shifts. We describe a marking and identification prototype that implements the proposed method. We present preliminary experimental results which suggest that centroid detection performs remarkably well on line shifts even in the presence of severe distortions introduced by printing, photocopying, scanning, and facsimile transmission.