Specification of initial connection handling in TCP using structured Petri nets

This paper uses structured Petri nets to specify how connection establishment is handled by the DoD Transmission Control Protocol. The purpose of this paper is to demonstrate an alternate specification technique by examining its application to a portion of a protocol of reasonable complexity.Initially we briefly present the semantics of structured Petri nets. Following this, a terse discussion of the problems of establishing connections in a network takes place. This discussion centers on the use of the three-way handshake, which is used by TCP, as a solution for many of these problems. Finally, the specification of the three-way handshake used in TCP is made. The specification is presented in three sections: first, a general set of notes concerning the nature of this particular specification is discussed; second, the data definitions of the specification are given; and, third, the actual nets themselves are presented.This paper is condensed from a portion of the author's dissertation, which is still in preparation. In the interests of brevity, some components of the specification, such a retransmission handling, have been omitted. Interested readers should contact the author for a more detailed paper

Low tech connections into the ARPA internet : the RawPacket split-gateway

This report describes a "low technology" method for connecting into the ARPA Internet. The use of a RawPacket interface in a system which supoprts IP makes possible the construction of a split-gateway between two hosts. The RawPacket interface permits a user-level process to introduce arbitrary packets into the IP layer, resulting in a virtual network interface. Since the split-gateway is implemented using a RawPacket interface, two networks may be connected together using a convenient medium which does not require explicit kernel support. Hence, split-gateways are well-suited for use as stub-gateways, connecting a local network to a long-haul network such as the ARPA backbone. In particular, the split-gateway discussed in this report achieves a reasonable level of connectivity for a comparatively small expenditure.This report details how the RawPacket software and split-gateways are implemented. In addition, various daemon configurations are presented, modifications to the operating environment are discussed, and some performance measurements are given

Casting Polymer Nets to Optimize Noisy Molecular Codes

Life relies on the efficient performance of molecular codes, which relate symbols and meanings via error-prone molecular recognition. We describe how optimizing a code to withstand the impact of molecular recognition noise may be approximated by the statistics of a two-dimensional network made of polymers. The noisy code is defined by partitioning the space of symbols into regions according to their meanings. The "polymers" are the boundaries between these regions and their statistics defines the cost and the quality of the noisy code. When the parameters that control the cost-quality balance are varied, the polymer network undergoes a first-order transition, where the number of encoded meanings rises discontinuously. Effects of population dynamics on the evolution of molecular codes are discussed.Comment: PNAS 200

Cotton spinning to climbing gear: practical aspects of design evolution in Lancashire and the North West of England

This article looks at the role of path dependency in the design of outdoor clothing and equipment, from the perspective of changing and overlapping industrial clusters in Lancashire and Sheffield, from the 1960s. It demonstrates that, unlike the fashion market, design in mountaineering clothing and equipment was originally based heavily upon functionality and hence on user innovation. It shows that skills and knowledge which evolved during the industrial revolution, in both industrial areas, were vitally important to the development of internationally competitive mountaineering equipment firms. It was, however, the way in which these sources of knowledge were combined with sporting expertise that contributed to the design of innovative functional products. In addition, fundamental changes occurred in the relationship between manufacturers and their customers and these were vital to the success of this process, marking a departure from past practice

A finite difference scheme for the equilibrium equations of elastic bodies

A compact difference scheme is described for treating the first-order system of partial differential equations which describe the equilibrium equations of an elastic body. An algebraic simplification enables the solution to be obtained by standard direct or iterative techniques

Evaluating copper isotope fractionation in the metallurgical operational chain: An experimental approach

Until today, raw material information of copper (Cu) objects is mostly gained from impurities and trace elements and not from the Cu itself. This might be obtained using its stable isotopes. However, isotopic fingerprinting requires the absence of fractionation during the smelting process. The Cu isotope evolution during outdoor smelting experiments with Cu sulphide ore was investigated. It is shown that external materials, in particular furnace lining, clay, manure and sand, alter the isotopic composition of the smelting products. Cu isotopes are fractionated within low viscosity slag derived from matte smelting. The produced metallic Cu has a Cu isotope signature close to the ore

A compact finite difference scheme for div(Rho grad u) - q2u = 0

A representative class of elliptic equations is treated by a dissipative compact finite difference scheme and a general solution technique by relaxation methods is discussed in detail for the Laplace equation

An approximate solution for interlaminar stresses in laminated composites: Applied mechanics program

An approximate solution for interlaminar stresses in finite width, laminated composites subjected to uniform extensional, and bending loads is presented. The solution is based upon the principle of minimum complementary energy and an assumed, statically admissible stress state, derived by considering local material mismatch effects and global equilibrium requirements. The stresses in each layer are approximated by polynomial functions of the thickness coordinate, multiplied by combinations of exponential functions of the in-plane coordinate, expressed in terms of fourteen unknown decay parameters. Imposing the stationary condition of the laminate complementary energy with respect to the unknown variables yields a system of fourteen non-linear algebraic equations for the parameters. Newton's method is implemented to solve this system. Once the parameters are known, the stresses can be easily determined at any point in the laminate. Results are presented for through-thickness and interlaminar stress distributions for angle-ply, cross-ply (symmetric and unsymmetric laminates), and quasi-isotropic laminates subjected to uniform extension and bending. It is shown that the solution compares well with existing finite element solutions and represents an improved approximate solution for interlaminar stresses, primarily at interfaces where global equilibrium is satisfied by the in-plane stresses, but large local mismatch in properties requires the presence of interlaminar stresses