Showing papers in "Computer Networks and Isdn Systems in 1986"

A survey of multi-connected loop topologies for local computer networks

Abstract: Loop network architectures are an attractive topology for local computer networks because they require simple interfaces and control. Single loop networks tend to become unreliable when the number of nodes in the network becomes large. Multiconnected loop topologies have been proposed for improved reliability and performance. There are several double loop networks based on forward loop backward hop topology, with a loop in the forward direction connecting all the neighboring nodes, and a backward loop connecting nodes that are separated by a distance h. This paper presents a systematic study of single and double loop networks and also discusses various other loop networks with higher connectivities.

Reliability mechanisms of the FDDI high bandwidth token ring protocol

Abstract: The Fiber Distributed Data Interface (FDDI) is an ANSI draft proposed standard for a 100 megabit per second token ring using fiber optics as the transmission medium. The FDDI design represents an extensive effort to incorporate reliability mechanisms as an integral part of the design. These mechanisms provide fault detection and isolation functions, monitoring functions, and configuration functions. The purpose of this paper is to discuss these reliability mechanisms, and to compare and contrast them with reliability mechanisms which have been incorporated in other local area network architectures.

Establishing virtual circuits in large computer networks

Abstract: Network routing algorithms generally attempt to provide communication between two nodes by sending data messages along the best or shortest path between them. Unfortunately, in large networks it is difficult to maintain knowledge of such path due to the cost in storage, computation, and communication bandwidth. In an attempt to solve this problem the technique of clustering has been proposed. Clustering generally reduces the cost of routing of by sacrificing optimality. Kamoun has shown that this sacrifice is asymptotically negligible under certain strong assumptions. In this paper we propose a new clustering technique which permits us to obtain optimal paths. However, determining these paths requires some effort and thus the methodology is appropriate only if the paths are then used for many messages in virtual circuit fashion. An application to planar networks gives a quantitative demonstration of obtaining optimal paths with reduced path determination cost.

Implementation of a dynamic address assignment protocol in a local area network

Abstract: This paper describes the implementation of a dynamic address assignment protocol (DAAP) on a prototype local area network. A DAAP permits the use of shorter addresses on each packet, which can lead to reduced overhead on networks that support short packets. The protocol described can be applied to any network which permits one station to be distinguished from a set of several stations using the same address. In a network using dynamic addresses a station may arbitrarily use a wrong address; the ensuing problems are discussed.

Optimal design parameters in a multishop packet radio network using random access techniques

Abstract: Takagi and Kleinrock studied the problem of optimal transmission ranges in a packet radio network with mobile terminals, assuming that each terminal is equipped with an omidirectional antenna. The purpose of this paper is to examine the possible improvement gained by directional antennas. The protocols considered include slotted ALOHA (with and without capture) and non-persistent CSMA. Results show throughput performance can be greatly enhanced by proper directional antennas. Two routing strategies, most-forward-routing and point-to-destination, are investigated and compared. The study shows both strategies posses roughly the same degree of performance. However the latter is attractive for its simplicity of system operation.

OSI transport services on top of the TCP

Abstract: The ARPA Internet community has a well-developed, mature set of transport and internetwork protocols, which are quite successful in offering network and transport services to end-users. The protocols provide “open system interconnection” (OSI) for users, and a robust competitive market is supplied by a growing number of vendors. The CCITT and ISO have defined various network, transport, session, presentation, and application recommendations and standards which have been adopted by the international community and numerous vendors. To the largest extent possible, it is desirable to offer the higher level services (i.e., session and above) in networks based on the ARPA protocols, without disrupting existing facilities. It is also desirable to develop expertise with ISO and CCITT protocols while utilizing a robust set of transport services. Finally, given the probable, long-term dominance of the international standards, it is desirable to design a graceful transition strategy from network based on the ARPA protocols to OSI-based networks. In this paper, we suggest an exercise in interoperability which achieves all three of these goals. Our solution is practical in the sense that it: can be easily implemented in a cost-effective manner in the short-term; permits application-designers to work with an OSI applications-framework, while utilizing existing robust transport and network protocols; and, provides the basis for a far-reaching migration strategy to the OSI protocols.

Analysis and control of traffic routing in circuit-switched networks

Abstract: The presented paper is concerned with qualitative and quantitative analysis of advanced traffic control concepts. In the first part a survey of traffic control techniques is made with the final aim of separating the factors influencing the network grade of service. The second part is devoted to the performance evaluation of adaptive routing in two trial networks. The simulation is used to highlight the significance of network structure, signalling techniques, multiple overflows and update cycle length for the efficiency of a flexible routing rule.

Subtle design issues in the implementation of distributed, dynamic routing algorithms

Abstract: The design of distributed, dynamic routing procedures is highly complex, due to the fact that it relies on cooperation among a number of independent processors located at the nodes of communication networks and the fact that a network may face arbitrary topological changes. As a result, many simple, intuitive, concepts that seem, at first glance, that they should result in correct algorithms do not work. This paper evaluates this theme by exploring a number of examples of this phenomenon. The conclusion is that one must be careful both in the overall design of a distributed algorithm, and in its detailed implementation. This also illustrates the importance of careful formal validation of such protocols, rather than informal, intuitive arguments.

Performance evaluation of channel access schemes in multihop packet radio networks with regular structure by simulation

Abstract: The performance of various channel access schemes in multihop packet radio networks with a regular structure is studied by means of simulation. The channel access schemes considered are: ALOHA (pure and slotted), Carrier Sense Multiple Access (CSMA), Busy Tone Multiple Access (BTMA), Code Division Multiple Access (CDMA), and a new hypothetical scheme introduced here for comparison purposes referred to as Coded Activity Signalling Multiple Access (CASMA). Network throughput and packet delay are evaluated, as well as the effects on performance of the nodal transmission scheduling rate, the propagation delay among nodes, and to some extent the input flow control. In this study, we consider networks in which both the topology and the traffic pattern are symmetric. This render all nodes in the network statistically identical, and thus helps reduce the complexity of the simulation task considerably without jeopardizing the objective. The performance of CSMA in such networks in shown to be rather poor as compared with its performance in fully connected networks, while relatively high performance is achieved by the CASMA scheme, the various BTMA protocols, as well as the CDMA scheme, as compared with CSMA and the ALOHA schemes.

Authentication protocols for computer networks: I

Abstract: Specifications of encryption-based protocols using conventional and public-key encryption schemes are discussed for authentication of users or systems in a computer network environment. The protocols treat a sender and a receiver symmetrically and make no assumption about any specific time ordering of events. We apply state machine modeling and analysis techniques to determine important properties of these protocols including completeness, deadlock freeness, livelock or tempo-blocking freeness, termination, boundedness, and absence of non-executable interactions.

Step-wise validation of communication protocols and services

Abstract: A highly automated approach is proposed for testing the consistency of distinct representations of identical system functionality. This approach is based on dynamic comparison and analysis of observable behaviors presented by system functionality representations given at different levels of abstraction. These representations are encoded in a relatively mechanical way as procedures in sequential PROLOG and thus provide the capability of generating and checking the system functionality they capture. The approach is extremely flexible, straightforward to use, and particularly appropriate to systems whose externally observable behavior can be modeled by finite state automata. The use of this approach is illustrated in the context of OSI communication protocol design and validation.

The flooding sink-A new approach to local area networking

Abstract: A new local area networking technology is presented. The approach is based on an old routing algorithm called flooding — forward messages to all neighbouring nodes. The problem with this algorithm is that the network is deluged with duplicate messaes. The solution is a simple device which uses local memory to detect and ignore redundant messages, thus also acting as a message sink. Networks based on this device can be more flexible and reliable than current networks. Flooding also has the advantage that any messages lost due to transmission errors are quickly replaced by one of the copies. This can make low-level protocols unnecessary. When the low-level protocols are omitted, significant performance improvements are achieved. Simulation results are presented which show that this flooding technology can perform better than current CSMA and ring technologies.

A congestion-control policy on the internetwork gateway

Abstract: A new approach to congestion-control policy for the interconnected networks system, called “FCP”, is proposed. The main purpose of the FCP policy is to avoid the congestion of a network as well as to guarantee the performance of each network up to the desired value. In FCP policy, the traffic that arrives at aateway is restricted by that gateway in compliance with the acceptable rate, called “PAR”, corresponding to its destination network. And the PAR corresponding to a network is determined based on the performance requirement of that network. The determination of PAR in FCP policy is presented and analyzed quantitatively in terms of network throughput, whereby the queuing models for a gateway and a network are developed. The result of the analytical evaluation of FCP policy is reduced to the problem of solving simultaneous non-linear equations with several variables and of a higher degree. Therefore, the systematic algorithm for computing PARs in FCP policy is also given. The numerical applications demonstrate the good efficiency of FCP policy to achieve the desired performance for each network.

Protocol analysis and synthesis by structured partitions

Abstract: Protocols can be viewed as predefined sequences of message exchanges between machines for performing network control functions and for providing network services. One way of modeling protocols is by using communicating finite state machines. The interaction between finite state machines can be very involved, even for machines with few states. To counteract the complexity for protocol analysis and synthesis, we propose a partitioning method based on protocol subgraphs. We found that if there are ‘cross interactions’ involving the entire protocol graph, then the protocol is not decomposable by our technique and must be analyzed or synthesized as a whole. However, if there are subunits of message exchanges within the protocol graph that are self-contained, in other words, if there are no ‘cross interactions’ between protocol subgraphs, then the protocol is decomposable. For protocols that are decomposable, we show that it is only necessary to examine a subspace of the entire reachability space to understand the behavior of the protocol and to guarantee its progress properties. This allows us to analyze and synthesize protocols based on these subgraphs.

Multirate voice coding for load control on CSMA/CD local computer networks

Abstract: A study of mixed voice and data on a local area network using Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is presented. The study determined the feasibility of applying multirate voice coding to control the traffic intensity on the network. By decreasing the voice coding rate for short periods of time (and thus the voice quality) when network traffic increases, a larger number of voice users can be realized. The premise is that short term voice quality can be traded for increased throughput on a CSMA/CD network. Collisions per millisecond was found to give a good indication of the traffic on the network. A feedback equation is used to set the voice coding rate, based on the measured collisions per millisecond. The coding rate determined from the feedback equation is rounded to one of four possible coding rates; other rates are clearly possible. The voice coding rates chosen were 48, 40, 32, and 24 kilo-bits-per-second. The simulation results show that additional voice users can be added to a 1 mega-bit-per-second network when the multirate algorithm is used. Results are given relating the packet delay to the collisions per millisecond. A comparison between multirate and non-multirate is given. An indication of the voice quality for the multirate system is also discussed. The multirate load control algorithm provides a way to increase the amount of voice traffic on a CSMA/CD network.

Analysis of a Hybrid (demand assignment TDMA) protocol for video teleconferencing-voice data optical networks

Abstract: An optical star connected backbone network has recently been designed [1] and is currently being built. Though the network is local, it is mainly intended for internetworking applications. A large number of local networks such as Ethernet or other integrated voice data networks can be interconnected via the local optical network. Also, because of the enormous bandwidth available, point to point and conference video users can be easily accomodated (simultaneously operating with the other applications). To be able to accommodate such huge services, the central switch and the 16 data concentrators of the proposed network have a great deal of software protocols to execute. The heart of these procedures is a hybrid (demand assignment — TDMA) protocol. The object of this paper is to give a concise picture of the network, the protocols involved and more importantly, to evaluate the throughput efficiency and delay characteristics.

Testing to assure interworking of implementations of ISO/OSI protocols

Abstract: At the Institute for Computer Sciences and Technology of the national Bureau of Standards, an architecture has been specified for testing protocols in layers four through seven of the International Organization for Standardization's (ISO) Basic Reference Model for Open Systems Interconnection (OSI). This paper describes the application of that architecture to testing Class 4 Transport with thirteen vendors' implementations of the protocols prior to a demonstration of ISO protocols at the National Computer Conference in 1984. The test results are summarized and an evaluation of the architecture and individual tools is presented. The paper concludes with a summary of a more ambitious demonstration of networking using implementation of ISO protocols.

Analysis of dynamic behavior in p-persistent CSMA/CD using cusp catastrophe

Abstract: The dynamic behavior of p-persistent CSMA/CD is considered through application of the cusp catastrophe. Applying the cusp catastrophe, we find that the system state changes from monostable to bistable as the packet arrival rate increases for a given packet retransmission rate but not for another. In order to find an explanation for the sudden performance deterioration for one system state but not another, we examine system performance according to type of transition of the system state - the mean backlog, throughput and mean packet delay. We then consider a control strategy for avoiding drastic performance deterioration. Finally we consider the dependence of the stability of the system state on such system parameters as number of nodes and packet length.

A validation of the OSI session layer protocol

Abstract: The session layer of the ISO Open-System-Interconnection (OSI) Protocol has been validated using an automated state-exploration technique. The validation methodology is described, together with the particular way it has been applied to the session layer. A number of the protocol errors found is presented.

Carrier sense access in an enviornment of two interfering channels

Abstract: Interference problems in radio networks are investigated. A general model is developed for the case of two interfering channels. The model is used to analyzed the performance of a two-station packet radio network and a CSMA network with hidden terminals. Performance evaluations for both slotted and unslotted systems are presented.

Effect of propagation delays on ALOHA systems

Abstract: Effect of propagation delays on the steady state behavior in ALOHA systems is investigated. The basic model of ALOHA systems with propagation delays is introduced and analyzed in line with the catastrophe theory. The bifurcation set, which shows the necessary and sufficient condition that the system is either monostable or bistable, is given explicitly in terms of a few system and user parameters including propagation delays. The global behavior of the system is determined by the cusp catastrophe. Analysis of bifurcation sets shows that propagation delays stabilize the system.

Synchronous communication protocols for local networks

Abstract: We propose protocols for the synchronous transmission of voice packets in local area networks. Two network models are considered: an all-voice network and a mixed voice and data network. The performance of the protocols is evaluated via simulation for these two network models.

CSMA/CD LANs with overload detection and protection

Abstract: Classic Markovian models for CSMA/CD LANs are modified to handle a finite number of stations with dissimilar arrival rates among the stations. Simple rules are derived for overload detection and protection of a CSMA/CD LAN. It is demonstrated that a station can correctly determine the total network load and decide whether the medium is currently overloaded or not. A fair share algorithm is suggested for every station in a CSMA/CD LAN to protect the medium from being overloaded. With proper overload protection, it is shown that the expected penalty due to collisions for each successful transmission is geometrically distributed. In conclusion, this analysis shows that the performance of CSMA/CD LANs is significantly better than predicted by simpler models and it can be improved by a simple modification to the standard CSMA/CD protocol.

Software development and implementation of NBS class-4 transport protocol

Abstract: The International Standards Organization has developed a 7-layer reference protocol model for computer communications. The transport protocol, the fourth-level protocol in this reference model, provides a reliable end-to-end communications path between two user processes in different hosts. This paper describes the software development and implementation of the National Bureau of Standards (NBS) class-4 transport protocol (TP-4) for a joint COMSAT/NBS experiment. It includes: transport protocol mechanism, relevant hardware and software environment, transport protocol software development stage, correctness test, the use of satellite protocol delay simulator for software tuning, and a brief description of the satellite experiment.

Network testing system for digital data networks

Abstract: The digital data exchange network testing systems (DNTS) is developed to enhance service quality and reduce maintenance costs in digital data networks. DNTS achieves quick, accurate and systematic fault detection and localization in networks by integrating network test facilities such as terminal, transmission and switching test facilities. Remote and automatic test control of the DNTS not only accelerates fault detection and localization processes but reduces maintenance costs to a remarkable degree. The DNTS has been developed mainly for testing digital data networks, but the system architecture developed in the DNTS is also applicable to the ISDN testing system.

Grade of service and optimization of distributed packet-switched networks

Abstract: Packet-switched network optimization leads to specific problems related notably to the quality of service requirements to be take into account. The aim of this paper is to present methods for taking these quality of service constraints into account in the optimization process, particularly for heterogeneous networks (i.e. networks using several types of switch and several line capacities). These methods are based on the notion of diameter of graphs, and have been implemented in the computer programs Credo and Credo H, developed by CNET and currently used to plan the French public packet-switched network Transpac.

Local digital telephone system on two-way cable television

Abstract: A telephone transmission system using several 6 MHz video bands and return channels in a cable TV distribution line is proposed. In this system, cable TV is used for subscriber accomodation with a local telephone system. In order to realize high accomodation capability in a conventional tree-shaped CATV network, we adopt a two-level structure for the voice distribution, and use a distinct media access protocol for each level: the logical loop scheme for the higher, and the polling-selecting scheme for the lower. The design concept of this system has compatibility with any existing CATV installations, and can be flexibly applied to them. Based on the analysis of the accomodation capacity of the above two media access protocols, a CATV local telephone network for a medium-scale local switch is designed. This system is expected to give one of the most economical subscriber distribution capabilities with integrated telephone and video service.

Simulation of distributed processing networks

Abstract: A discrete event simulator named DDPSIM for distributed processing networks is presented. The simulator which was initially developed to support the design of a distributed processing system for an air defense application, has continued to evolve to accommodate a more general class of bus-connected networks in which software modules, or tasks, are distributed. It has also been used to model a complex air traffic control application which involved multiple networks. The modular organization and various distributed network component models of the simulator are described in detail. The simulator provides user friendly interfaces that include simple input conventions for system definition, and tabular and graphic outputs for comprehensive analyses of the simulation results. A relatively complex distributed processing system for air traffic control is used as an example to illustrate the simulation procedure and to show the simulation results. To conclude, the lessons learned from the experience in simulation are discussed.

Secury mechanisms for computer networks (a program of the CEC COST-11 Ter project)

Abstract: This paper is based on the Proposal made by the Working Group to the CEC COST-11 Ter Concentration Committee in November 1985. The Propoposal was accepted and the official COST-11 Ter Project started at the beginning of 1986. This paper describes some interesting details of the Project: objectives and goals of the Project, its topics, participating institutions, timeschedule, milestones, and expected results. The main purpose of this paper is to initiate a broader cooperation in Europe through exchange of ideas, solutions, research papers or experience in the area of computer networks security.