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ND OSI Transport Service

ND 211023

The Reference Model for Open Systems Interconnection

flowchart TB
    subgraph SystemA [System A]
        direction TB
        A1(Application Layer)
        B1(Presentation Layer)
        C1(Session Layer)
        D1(Transport Layer: ND OSI Transport Service)
        E1(Network Layer: X.25 Packet)
        F1(Data Link Layer: X.25 Link HDLC)
        G1(Physical Layer: V.24/X.21)
    end

    subgraph SystemB [System B]
        direction TB
        A2(Application Layer)
        B2(Presentation Layer)
        C2(Session Layer)
        D2(Transport Layer: ND OSI Transport Service)
        E2(Network Layer: X.25 Packet)
        F2(Data Link Layer: X.25 Link HDLC)
        G2(Physical Layer: V.24/X.21)
    end

    A1 <--> A2
    B1 <--> B2
    C1 <--> C2
    D1 <--> D2
    E1 <--> E2
    F1 <--> F2
    G1 <--> G2

    PhysicalMedia([Physical Media for OSI]):::sub

[Logo: Norsk Data]

Scanned by Jonny Oddene for Sintran Data © 2010

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ND OSI Transport Service

Introduction

The ND OSI Transport Service enables programs running on ND computers to communicate with programs running on computers sold by other vendors, and with programs running on other ND computers. The product is a set of software tools designed to achieve this communication. It completely conforms to the transport layer of the seven-layer Open Systems Interconnection (OSI) protocols, defined by the International Standards Organisation (ISO 8072).

The ND OSI Transport Service provides the Transport Layer of the OSI seven-layer model. This product has two parts: The OSI Transport Library (OSI-TLIB), and the OSI Transport Server (OSITS).

The OSI Transport Service runs on the full range of ND systems, from the Satellite models up to the ND-500 model range.

Features

The ND OSI Transport Service has the following features:

  • Provides for communications with non-ND systems across an X.25 packet-switched Wide Area Network (WAN).
  • Allows user programs to communicate over COSMOS (ND's proprietary networking system) with other ND computers.
  • Allows communication from one process to one or several other processes over a variety of networks. This communication is transparent to the user.
  • Provides user interfaces to programs written in PLANC, as well as in other high-level languages like FORTRAN, PASCAL, and COBOL.
  • Conforms to Class 0 and Class 2 of the OSI Transport Protocol.
  • The OSI transport library and the COSMOS transport library are compatible.
  • The System Supervisor controls the action of the OSITS by using the XMSG (ND's proprietary message-switching system) command program. This command program has functions to define routes to remote systems, and to start/stop OSITS.
  • One program can have several logical connections over one network connection.
  • Several programs may share a single network connection.

Description

The ND OSI Transport Service comprises the OSI Transport Library (OSI-TLIB) and the OSI Transport Server (OSITS).

The OSI-TLIB is a set of subroutines that can be called by a user program to set up transport connections and to pass data between the connected programs. It uses (XMSG) to carry the OSI Transport Protocol messages. Thus, it is used in a similar way as the COSMOS Transport Library (TLIB) for communication between programs in ND computers. Within one machine, the data will be passed using single system XMSG.

flowchart LR
    A(User Program)
    B(User Program)
    C(OSI-TLIB)
    D(COSMOS-TLIB)
    E[Inter-system XMSG]

    A --> C
    B --> D
    C --> E
    D --> E

Two sets of routines are provided in the OSI-TLIB part of the ND OSI Transport Service. One of these sets is used by programs written in PLANC (ND’s internal systems programming language). The other set is used by programs written in FORTRAN, PASCAL, or COBOL. Both sets of user routines provide a user interface that complies with the requirements of the OSI Transport Service Definition (ISO 8072).

To ease the transition from COSMOS-TLIB to OSI-TLIB, the user program interfaces of the two libraries are compatible. This enables user programs that call COSMOS-TLIB routines to call OSI-TLIB routines instead, simply by recompiling and relinking. A user program calling OSI-TLIB can also connect to, and exchange data with, a program calling COSMOS-TLIB.

flowchart LR
    A(User Program)
    B(User Program)
    C(OSI-TLIB)
    D(OSI-TLIB)
    E(XMSG)

    A --> C
    B --> D
    C --> E
    D --> E

The OSI Transport Server (OSITS) is a real-time program used to convert the XMSG protocol messages, produced by OSI-TLIB, into OSI Transport Protocol passed over X.25 to a remote computer. The protocol conforms to the OSI Transport Protocol Specification (ISO 8073). OSITS must be used in conjunction with OSI-TLIB when communicating with a non-ND system that supports the OSI Transport Protocol. The use of OSITS is transparent to the user programs.

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ND OSI Transport Service

Requirements

  • ND Systems running SINTRAN Version J or later.
  • XMSG Version J or later.
  • COSMOS X.25 Option Version B or later.

Documentation

Manuals

Document Code
OSI Transport Service Programmer Guide ND-60.237 EN
OSI Transport Service Operator Guide ND-30.050 EN

Relevant Manuals

Document Code
COSMOS Operator Guide ND-30.025 EN
COSMOS X.25 Option Operator’s Guide ND-30.034 EN

OSI Reference Documents

  • OSI Transport Protocol Specification (ISO 8073)
  • OSI Transport Service Definition (ISO 8072)
graph TD;
    A(User Program) -->|XMSG| B(OSI Transport Server);
    B -->|XMSG| C(X.25);
    A1(User Program) -->|XMSG| B;
    C -->|To non-ND Computer| D;

Single ND System Communicating with a non-ND System

The OSITS supports class 0 and Class 2 of the OSI Transport Protocol. Class 0 supports basic functions and can be used when a reliable network can be assumed. Class 2 service allows multiplexing of several transport connections, from the same or from different user programs, over one network connection. It also provides flow control of data transferred over each transport connection. A logging facility is provided that can be used to keep a record of the actions performed by OSITS.

Conformance to OSI Standards

The ND OSI Transport Service conforms to the OSI Transport Service (ISO 8072) as defined by the ISO. This conformity includes the following points:

  1. The Transport Protocol used over X.25 to communicate with a remote computer conforms to Classes 0 and 2 of the OSI Transport Protocol Specification (OSI 8073).
  2. The software is capable of both initiating and responding to Transport Connection Requests.
  3. Extended formats and Non-use of Flow Control (optional features of the Class 2 protocol) are not implemented.
  4. The maximum TPDU (Transport Protocol Data Unit) size supported is 512 bytes.

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Norsk Data Contact Information

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