Terminal Protocol Research Articles

Site optimal termination protocols for a distributed database under network partitioning

Partition failure causes a major problem for the availability of a distributed database system. No protocol can consistently terminate all parts of a distributed transaction under all possible partitions, since some sites executing subtransactions may not know that other sites have already committed (or aborted) and, therefore, must wait until the failure is repaired. Under a site optimal termination protocol, the expected number of waiting sites is minimized, hence it maximizes the "availability" of a database system in the presence of partition failures. We introduce a new class of partition failures. We introduce a new class of termination protocols, called size-based termination protocols, and identify site optimal termination protocols within this class.

Mutual exclusion in partitioned distributed systems

A network partition can break a distributed computing system into groups of isolated nodes. When this occurs, a mutual exclusion mechanism may be required to ensure that isolated groups do not concurrently perform conflicting operations. We study and formalize these mechanisms in three basic scenarios: where there is a single conflicting type of action; where there are two conflicting types, but operations of the same type do not conflict; and where there are two conflicting types, but operations of one type do not conflict among themselves. For each scenario, we present applications that require mutual exclusion (e.g., name servers, termination protocols, concurrency control). In each case, we also present mutual exclusion mechanisms that are more general and that may provide higher reliability than the voting mechanisms that have been proposed as solutions to this problem.

OSI virtual terminal service

The OSI Virtual Terminal Service (VTS) is one of several application-oriented communication services being provided by protocols operating in the Application Layer of the Open System Interconnection Environment. There will be several Virtual Terminal services and protocols, each catering to a different class of distributed terminal service. Division of the VTS into classes of service allows more timely, economical, and efficient support of distributed terminal service, both now and for the future. Current work is concentrating on the Generic Virtual Terminal Protocol and the Basic Class Virtual Terminal Protocol. The Generic Virtual Terminal Service and Protocol establishes the general approach to providing all classes of VTS and sets the style for generating Virtual Terminal Protocols (VTP's) for Specific classes of terminal use. The Basic Class VTP is the first OSI VTP being developed by the International Organization for Standardization, and is intended to provide distributed terminal access for a wide range of nonsophisticated character-oriented terminals.

Terminal Protocols

Terminal protocols provide basic services for the users of computer networks. This paper presents a survey of the architecture and mechanisms used in current terminal protocols. The paper disusses both parametric terminal protocols such as the CCITT X.3, X.28, and X.29 and virtual terminal protocols, such as the ARPANET TELNET protocol. Many of the problems encountered in terminal protocols recur in more complex forms in the more sophisticated protocols.

DCNA Higher Level Protocols

This paper explains a philosophy for modeling the higher level communication functions into a network architecture for heterogeneous computer networks called Data Communication Network Architecture (DCNA), the logical structure of the architecture, and several protocols based on it. To specify higher level protocols among computers of different types, DCNA defines a logical model of a computer network consisting of three submodels: the basic model, the logical network model, and the virtual network model. The basic model represents a logical view of the network resources, e.g., processing power, files, data bases, I/O devices, and a layered structure for the basic mechanisms for accessing such resources, which incorporate the concept of sublevels as well as levels. The logical network model describes the mechanisms for unified management of network resources. The virtual network model describes the mechanisms for using network resources. The. common use of network resources, by several sets of interrelated applications is made easier by treating the logical network and the virtual network separately. These models form the basis for the stipulation of higher level protocols, such as network management protocols, message transfer protocols, virtual terminal protocols, and virtual file system protocols.

Virtual terminal protocols transport service and session control

The methods to identify the different terminal protocols for EURONET and the parameter selection mechanism in VPT-D, particularly the terminal mode, are discussed. Based on this, the problems concerning protocol shift are investigated. An integrated solution is outlined and the ISO Reference Model of Open Systems Interconnection is enhanced.

A survey of terminal protocols

The Virtual Terminal approach has been used by first by the ARPANET in the U.S. In the last few years, the problem of defining Virtual Terminal Protocols has been approached by several international organizations such as EIN, Euronet, IFIP and by national organizations such as the Belgian University Networks, the German PIX Network, the French Cyclades Network and INFORREP (french' user association'). Asociated manufacturers have also presented a proposal. Till now, an internationally accepted Virtual Terminal Protocol has not yet emerged. The aim of this paper is to compare different protocols. It is divided into four main parts: 1. Presentation of the relationships between Virtual Terminal Protocol and network architecture. 2. Analysis of the different virtual terminal model. 3. Analysis of the set of primitives intended to data structure definition and management. 4. Introduction to the synchronization mechanisms of the protocol.

Remarks on negotiation mechanism and attention handling

Preliminary studies are at present being made for building a computer network linking the computer centres of the different Belgian Universities. This network would include:1. a packet switching network with the X25 service on top of it;2. a transport protocol;3. user level protocols (a virtual terminal protocol and a file transfer protocol).Cooperation between terminals and applications will be organized using a virtual terminal approach.Assuming a transport function offering:1. block transmission with error control on contents, error control on arrival and sequencing;2. telegram transmission with error control on contents and error control on arrival,we present the attention handling scheme proposed for the Virtual Terminal Protocol of the Belgian University Network.The proposed scheme includes a renegotiation of the data flow mode (free running or alternate).A detailed algorithmic description of the proposed attention handling scheme is given using a state diagram representation.

An informal comparison of three protocols

Three pairs of higher level computer communication protocols are compared to reveal design choices. The comparisons are between the host level protocols NCP and TCP used in the ARPANET, between the virtual terminal protocols Telnet and SMVT, and between the file transfer protocols FTP and BTF. The Telnet and FTP protocols are used in the ARPANET, while the SMVT and BTF are proposed for use in the EIN.

A virtual terminal protocol based upon the “communication variable” concept

The ideas presented here have emerged from discussions within the PIX working groups “Higher level protocols” and “Virtual Terminal protocol” and present the agreement of the PIX virtual terminal protocol. PIX = A cooperation between several network activities in the technical/scientific area in the FRG, sponsored by the Ministry of Research and Technology. The proposal is based on a general model of interprocess communication and describes how this model is used to fit the requirements of terminal control. The resulting class of terminal protocols uses one simple command set whereas the protocol for one specific terminal is derived by defining the appropriate data structure for that terminal. The complexity of a given terminal protocol therefore solely depends upon the complexity of its data structure. As an example, a protocol definition for a simple “line” and “page” mode terminal is given.

A File Transfer Protocol (FTP)

This paper presents a File Transfer Protocol (FTP) which can be used to transfer files between heterogeneous computer systems connected by a communication network. The basic mechanisms as well as the set of protocol commands and responses have been defined in the context of a general architecture. A simplified architecture, to help first implementations is also proposed. This can easily be extended to the more general one. The proposed protocol is completely compatible (even identical in some areas) with the currently proposed Virtual Terminal Protocol (VTP).

The virtual terminal approach in the Belgian University network

Preliminary studies are at present being made for building a computer network linking the computer centres of the different Belgian Universities. This network would include: 1. a packet switching network with the x25 interface; 2. a transport protocol at the user level; 3. application oriented protocols (e.g. virtual terminal protocol, file transfer protocol). Cooperation between terminals and applications will be organized using a virtual terminal approach. The aim of this paper is twofold: 1. to present the general concept of a virtual terminal and discuss its definition. Three classes of virtual terminal are introduced which exhibit increasing levels of terminal complexity (i.e. scroll mode, page mode and data entry); 2. to analyze fundamental protocol mechanisms (i.e. negotiation, data exchange synchronization and attention handling) with particular emphasis on attention handling. In this paper are mainly underlined the options which have been chosen for the Belgian University Network and the motivations which lead to make those choices.

High level protocol for alphanumeric data-entry terminals

In order to reduce possible incompatibilities between terminals and application programs, (AP), some networks have introduced the notion of the Virtual Terminal (VT) for scroll-mode terminals. The VT provides a standard representation of most current functions of terminals. This paper presents a Virtual Terminal corresponding to the class of intelligent terminals used for alphanumeric data-entry applications. These terminals consist of a screen and a keyboard, and may also include auxiliary devices such as printer(s), cassettes(s) and floppy disk(s). The VT model with its set of standard functions is described. A protocol VTP for exchanging and structuring the messages between VT and AP is also given. This VTP is independent of the communication means being used.

An RJE protocol for a resource sharing network

For many users of networks like the ARPANET, an RJE protocol is probably as important in terms of utility as the TELNET (or Virtual Terminal) protocol. In fact, the facilities provided by a TELNET and an RJE protocol are probably of most interest to the majority of users of computer networks. For these users, the network provides a fast, cheap telephone surrogate to a variety of computers for RJE and terminal access. The collection (and layers) of protocols that are used to provide these services must be organized to efficiently support a wide variety of applications and user needs. They should not pose an undue software burden on the user. The "official" NETRJE protocol for the ARPANET is built on top of the Telnet and File Transfer Protocols (FTP). A user of NETRJE establishes a Telnet connection using the User NETRJE program on his local host to a Server NETRJE process at the host where he wishes to submit a job (see Figure 1). The user then sends to the Server process appropriate commands to log in, to describe where the job is that is to be submitted, to describe how the job is to be transferred, and to describe what is co be done with output when the job is completed. The Server NETRJE process on the foreign host then uses the FTP to transfer the input file to the foreign host, and then may use FTP again later to send the output back to the user. This protocol is very general and allows a user to submit his input from one host, process it at a second, and send the output to a third.

Proposal for a scroll mode virtual terminal

The scope of this document is to present the concepts of a Virtual Terminal and to define in detail that portion of the Virtual Terminal Protocol which is adequate to support a basic Scroll Mode Virtual Terminal.

A virtual terminal protocol based on the use of zones

Companion papers have considered the concept of the Virtual Terminal in the context of a network (ref 1) and as an interface between users and computers (ref 2). These papers give a background for the present paper which proposes a Virtual Terminal protocol for use between an applications program and a remote terminal handler, based on the concept of the dynamic assignment of zones, introduced by Luca (ref 3). The paper by Luca contains an excellent discussion of the concept and use of zones, which seem well suited for a Virtual Terminal protocol although this was not considered in his paper. Some simplification of Luca's work is appropriate because he is concerned both with the interface between an application and the terminal handler, which he calls the programmable communications controller (PCC), and with the mapping between the PCC and a real terminal. The first aspect only will be considered here as the basis of a simple applications level protocol for a Virtual Terminal. However, Luca's paper is also a useful guide for the designers of the terminal handler and users who are concerned with mapping the Virtual Terminal onto particular real terminals. This paper draws on the ideas contained in the earlier papers reviewed in Appendix 1 of ref 2, and uses the notation introduced in Appendix 2 of ref 2. The zones concept is similar to the idea of the Communication Unit introduced by Schulze (ref 4) and this has also influenced the proposals set out below.