Distributed Data Processing (DDP-PPC) TCP/IP Interface COBOL

Transcription

1 !()+ OS 2200 Distributed Data Processing (DDP-PPC) TCP/IP Interface COBOL Programming Guide Copyright ( 1997 Unisys Corporation. All rights reserved. Unisys is a registered trademark of Unisys Corporation. Level 7R1 September 1997 Priced Item Printed in U S America v100

2 The names, places, and/or events used in this publication are not intended to correspond to any individual, group, or association existing, living, or otherwise. Any similarity or likeness of the names, places, and/or events with the names of any individual, living or otherwise, or that of any group or association is purely coincidental and unintentional. NO WARRANTIES OF ANY NATURE ARE EXTENDED BY THE DOCUMENT. Any product and related material disclosed herein are only furnished pursuant and subject to the terms and conditions of a duly executed Program Product License or Agreement to purchase or lease equipment. The only warranties made by Unisys, if any, with respect to the products described in this document are set forth in such License or Agreement. Unisys cannot accept any financial or other responsibility that may be the result of your use of the information in this document or software material, including direct, indirect, special, or consequential damages. You should be very careful to ensure that the use of this information and/or software material complies with the laws, rules, and regulations of the jurisdictions with respect to which it is used. The information contained herein is subject to change without notice. Revisions may be issued to advise of such changes and/or additions. RESTRICTED - Use, reproduction, or disclosure is subject to the restrictions set forth in DFARS and /FAR and for commercial computer software. Correspondence regarding this publication should be forwarded to Unisys Corporation either by using the Business Reply Mail form included with this document, or by addressing remarks to Unisys Corporation, Tredyffrin/Malvern Product Information, Malvern Development Center, P.O. Box 203, Paoli, PA, 19301, U.S.A. Comments about documentation can also be sent through to aspgpi@unisys.com All terms mentioned in this document that are known to be trademarks or service marks have been appropriately capitalized. Unisys Corporation cannot attest to the accuracy of this information. Use of a term in this document should not be regarded as affecting the validity of any trademark or service mark.

3 Contents About This Guide :::::::::::::::::::::::::::::::::::::::::::::: xiii Section 1. Introduction 1.1. DDP-PPC and the COBOL Interface ::::::::::::: The TCP/IP Interface ::::::::::::::::::::::::: Overview of Program-to-Program Applications ::: Migration from DDN R1 to DDP-PPC 6R1 and Higher ::::::::::::::::::::::::::::::::::: 1-4 Section 2. Procedural Overview 2.1. DDP-PPC COBOL Program Structure ::::::::::: Copying Information Packets ::::::::::::::::::: Using the COBOL COPY DDN-PKTS Statement ::: Sample Information Packets Produced from Copy Verbs :::::::::::::::::::::::::::::::: Sample Initialization Packets ::::::::::::::::: Additional Working-Storage Items ::::::::::::: COBOL Verbs and Function Calls ::::::::::::::: Function Calls ::::::::::::::::::::::::::::: COPY Verbs :::::::::::::::::::::::::::::: Initializing Packet Field Values :::::::::::::::: 2-9 Section 3. Using DDP-PPC TCP/IP Function Calls 3.1. COBOL COPY Verbs and Function Calls :::::::::: Terminating a Conversation (DDN-ABORT) ::::::: Closing a Conversation (DDN-CLOSE) ::::::::::: Interrupting Current Processing without Closing (DDN-INT-PROCESS) ::::::::::::::::::::::: Opening a Conversation (DDN-OPEN) ::::::::::: Replacing a Program in a Conversation (DDN-PASSOFF) ::::::::::::::::::::::::::: v100 iii

4 Contents 3.7. Receiving a Message from a Host (DDN-RECEIVE) Sending a Message (DDN-SEND) ::::::::::::::: Detaching an Application Program from DDP-PPC (DDN-SIGNOFF) ::::::::::::::::::::::::::: Attaching an Application Program to DDP-PPC (DDN-SIGNON) :::::::::::::::::::::::::::: 3-27 Section 4. Designing and Writing the Application 4.1. Using a Block Diagram :::::::::::::::::::::::: Creating a Flow Diagram :::::::::::::::::::::: Using the Message Buffer Area ::::::::::::::::: Formatting and Defining the Buffer Area :::::::: Referencing the Buffer Area :::::::::::::::::: Writing a Program-to-Program Application ::::::: General Considerations ::::::::::::::::::::: Receiving Data from a Remote Host ::::::::::: 4-9 Method 1 :::::::::::::::::::::::::::::: 4-10 Method 2 :::::::::::::::::::::::::::::: Closing a Conversation ::::::::::::::::::::: 4-12 Section 5. Compiling and Executing Programs 5.1. Preparing Programs for Execution :::::::::::::: Calling TCP/IP functions only ::::::::::::::::: Calling TCP/IP and TAS Program Callable-Functions :::::::::::::::::::::: Run Streams for DDP-PPC COBOL Programs ::::: Banking Considerations ::::::::::::::::::::::: UCS COBOL :::::::::::::::::::::::::::::: ASCII COBOL ::::::::::::::::::::::::::::: 5-5 Appendix A. Conventions for Naming Hosts A.1. Introduction ::::::::::::::::::::::::::::::::: A-1 A.2. Host Identifiers ::::::::::::::::::::::::::::::: A-1 Appendix B. Program-to-Program Example B.1. Sample Program Run Streams ::::::::::::::::: B-1 B.2. Primary (Sending) Program Example ::::::::::: B-3 iv v100

5 Contents B.3. Secondary (Receiving) Program Example :::::::: B-7 Glossary Bibliography v100 v

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7 Figures 1-1. Capabilities of the Program-to-Program Facility ::::::::::::::::::::: COBOL Verbs and Function Calls :::::::::::::::::::::::::::::::: Referencing Information Packets through Function Call USING Clauses :: Typical Block Diagram for Program-to-Program Passoff Succession :::: Typical Program-to-Program Block Diagram ::::::::::::::::::::::: Typical Procedure Division Program-to-Program Flow Diagram (Part 1) :: Typical Procedure Division Program-to-Program Flow Diagram (Part 2) :: Compile, Collect, and Execute Stream for an ASCII COBOL Application Program :::::::::::::::::::::::::::::::::::::::::::::::: Compile, Link, and Execute Stream for a UCS COBOL Application Program :::::::::::::::::::::::::::::::::::::::::::::::: v100 vii

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9 Tables 1-1. Comparison of the DDN R1 and DDP-PPC 6R1 TCP/IP Interface :: Copy Verbs and Associated Function Calls and Information Packets ::::: Copy Verbs and Associated Error Codes :::::::::::::::::::::::::: v100 ix

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11 Examples B-1. ASCII COBOL Compile and Collect Stream for Primary Program :::::::: B-1 B-2. UCS COBOL Compile and Link Stream for Primary Program ::::::::::: B v100 xi

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13 About This Guide Purpose This guide is designed to instruct and guide you in using the Unisys OS2200 Distributed Data Processing Program-to-Program Communications (DDP-PPC) TCP/IP COBOL interface. It tells you how to write COBOL application programs that let you exchange data between programs on the host or on remote hosts. The DDP-PPC TCP/IP COBOL interface was previously part of the DDN 1100 product. This guide instructs an applications programmer how to: $ Use a Unisys-supplied COBOL copy library to insert pre-written information packets and function calls into an ASCII or Universal Compiling System (UCS) COBOL program $ Write a COBOL application program using the COBOL information packets and function calls $ Compile the program $ Execute the program Scope This guide provides detailed information on COBOL function calls and information packets. It describes how to organize the calls and packets to enable users to write customized COBOL applications that can exchange data between programs in a multihost network. The material covered in this Guide was previously contained in the OS1100 Defense Data Network (DDN 1100) COBOL Programming Guide. Audience The primary audience for this programming guide is the applications programmer. This person is typically a COBOL programmer with several years of experience. The person might have a limited knowledge of communications and is dependent on reading this documentation to be able to write a COBOL application with program-to-program communications. The secondary audience for this guide is the site administrator v100 xiii

14 About This Guide This person typically has network and data base management experience. The site administrator is responsible for installing and implementing new hardware and software, network management, data bases, and security. Prerequisites To use this manual, you must understand distributed data processing concepts and know how to write standard COBOL programs. How to Use This Guide Programmers should use this guide to learn how to design and construct program-to-program applications. The guide shows you how to use COBOL COPY verbs and function calls to insert and set information packets in your program. Use this guide also to learn how to compile, link, and execute your application program. Organization Section 1. Introduction Gives an overview of DDP-PPC, TCP/IP, and features of the COBOL interface. Also gives a brief overview of program-to-program applications and how to migrate programs written for the DDN R1 interface to the DDP_PPC 6R1 (and higher) TCP/IP interface. Section 2. Procedural Overview Discusses conventional COBOL versus DDP-PPC COBOL program structure. Describes how you use the working storage section and the procedure division in program-to-program applications. Section 3. Using DDP-PPC TCP/IP Function Calls Describes the COBOL function calls and the information packets that let you transfer data between COBOL programs in the same or remote hosts. Tells how to sign on and off; open, close, or abort a conversation; and interrupt a process without closing the conversation. Section 4. Designing and Writing the Application Discusses how to design the application and construct a basic program-to-program application. Section 5. Compiling and Executing Programs Describes the executive control language run stream used to compile, collect or link, and execute the programs. xiv v100

15 About This Guide Appendix A. Conventions for Naming Hosts Discusses how to name hosts and OS 2200 elements. Appendix B. Program-to-Program Example Contains a working example of a DDP-PPC TCP/IP COBOL program-to-program application. Related Product Information Note: For all manuals, use the version that corresponds to the release level of the product software in use on the system. The following manuals provide related information you may find helpful: OS 1100 Communications Management System (CMS 1100) Configuration Reference Manual ( ) An alphabetical reference manual that describes the network definition statements you use to configure CMS OS 1100 Communications Management System (CMS 1100) Installation and Configuration Guide ( ) Describes the installation and configuration process to install and configure CMS Explains the concepts, the tasks that form the process, and the key requirements for configuring protocols and features. OS 2200 Distributed Data Processing (DDP-PPC/DDP-FJT) DCA Interface COBOL Programming Guide ( ) Describes how to structure COBOL programs that run on the OS 2200 system and interface with the DDP-PPC software via the Distributed Communications Architecture (DCA) interface. OS 2200 Distributed Data Processing (DDP-PPC/DDP-FJT) Messages Reference Manual ( ) Describes the status codes, error messages, and informational messages for DDP-PPC and DDP-FJT. OS 2200 Distributed Data Processing (DDP-PPC) OSI Interface COBOL Programming Guide ( ) Describes how to write DDP-PPC/OSI application programs in COBOL to exchange data in a network that adheres to open systems interconnection standards v100 xv

16 About This Guide OS 2200 Distributed Data Processing (DDP-PPC) TCP/IP Interface C Language Programming Guide ( ) Describes how to write customized C language applications that can exchange data with other programs in the same or remote computers in a multihost TCP/IP network. OS 2200 Distributed Data Processing (DDP-PPC) TCP/IP Interface FORTRAN Programming Guide ( ) Describes how to write customized FORTRAN applications that can exchange data with other programs in the same or remote computers in a multihost TCP/IP network. OS 2200 Distributed Data Processing Program-to-Program Communications (DDP-PPC) Implementation and Administration Guide ( ) Describes procedures for configuring and operating in a DDP environment on OS 2200 systems. It lists the hardware and software requirements and tells how to: $ Initialize and terminate the DDP-PPC environment $ Manage normal DDP-PPC activity $ Perform error recovery and diagnostic procedures OS 2200 TCP/IP Application Services (TAS) COBOL Programming Guide ( ) Previous title: OS 1100 Defense Data Network (DDN 1100) COBOL Programming Guide. Describes how to write customized COBOL applications that can transfer files or process mail in a multihost TCP/IP network. OS 2200 TCP/IP Application Services (TAS) FORTRAN Programming Guide ( ) Previous title: OS 1100 Defense Data Network (DDN 1100) FORTRAN Programming Guide. Describes how to write customized FORTRAN applications that can transfer files or process mail in a multihost TCP/IP network. xvi v100

17 Section 1 Introduction 1.1. DDP-PPC and the COBOL Interface Distributed Data Processing Program to Program Communications (DDP-PPC) is a systems software product used to handle and control data throughout a distributed data communications network. The DDP-PPC COBOL interface accepts function calls from a COBOL program to: $ Communicate with other application programs $ Update records on the same or a remote host $ Pass data between programs quickly and easily The DDP-PPC COBOL interface uses either ASCII COBOL or Universal Compiling System (UCS) COBOL. The interface provides COPY verbs that are used in your application program to provide information packets and issue requests (function calls) to DDP-PPC. Application programs compiled with the COBOL program-to-program interface: $ Run on OS 2200 systems $ Communicate with peer programs written in COBOL or other languages $ Communicate with peer programs residing on local or remote hosts or nodes The DDP-PPC COBOL interface described in this guide uses the TCP/IP protocol for program-to-program communications. DDP-PPC also provides COBOL interfaces that use: $ Unisys Distributed Communications Architecture (DCA) protocol $ Open Systems Interconnection (OSI) protocol Those interfaces are described in the DDP-PPC/DDP-FJT DCA Interface COBOL Programming Guide and the DDP-PPC OSI Interface COBOL Programming Guide. DDP-PPC also provides FORTRAN and C language interfaces for program-to-program communications in a TCP/IP network. These interfaces are described in the DDP-PPC TCP/IP Interface FORTRAN Programming Guide and the DDP-PPC TCP/IP C Language Programming Guide respectively v100 1v1

18 The TCP/IP Interface 1.2. The TCP/IP Interface TCP/IP is a set of layered communications protocols originally defined by the Advanced Research Project Agencies (ARPA) of the United States Department of Defense (DoD). The Transmission Control Protocol/Internet Protocol (TCP/IP) element provides reliable communication between pairs of processes (applications). Thus, TCP/IP serves as the basis for the DoD concept of interprocess communications in communications systems. TCP/IP implements the transport layer in the hierarchy of layered protocols. It provides reliable connection-oriented, ordered, full-duplex data transfer, with capabilitiesfor flow control. TCP/IP, therefore, compensates for environments in which loss, damage, duplicated, or out-of-sequence data, and network congestion might otherwise occur. Consequently, it is well-suited to support military, governmental, and commercial applications. 1v v100

19 Overview of Program-to-Program Applications 1.3. Overview of Program-to-Program Applications The DDP-PPC TCP/IP program-to-program facility allows COBOL language application programs to pass data between programs in the same host or remote hosts in the network. For example, data may be status or informational messages, control information, or records from a file. This permits multiple message switching, status monitoring, or access to individual records of multiple files. Figure 1-1 shows the capabilities of the program-to-program facility. DDP-PPC TCP/IP Network Host Computer A Host Computer B COBOL Program A Data COBOL Program B Data COBOL Program C Figure 1-1. Capabilities of the Program-to-Program Facility Program-to-program facilities allow you to reconstruct files on the local host by using data gathered from many records, elements, or files on remote hosts. This eliminates duplication of large amounts of unnecessary and unwanted data. It also eliminates the need to use transportable mass storage devices, such as tapes or disks, to transfer data between hosts. The program-to-program facility lets you: $ Open, close, and terminate conversations $ Send and receive messages $ Access records at multiple sites to form a master file $ Access data bases at multiple sites for simultaneous real-time updates $ Attach and detach applications to DDP-PPC $ Interrupt current processing $ Replace a program in a conversation v100 1v3

20 Migration from DDN R1 to DDP-PPC 6R1 and Higher 1.4. Migration from DDN R1 to DDP-PPC 6R1 and Higher The DDP-PPC TCP/IP COBOL Programming interface was previously a component of DDN DDN R1 and DDP-PPC 5R1 used the GASIF interface to CMS. The GASIF interface is replaced by TSAM for DDP-PPC 6R1and higher. As a result, you may need to make certain changes in your TCP/IP programming application. (You must at least recompile current applications to pick up the new data and open packet sizes.) Table 1-1 summarizes the differences in the TCP/IP COBOL interface between DDN R1 and DDP-PPC 6R1and higher and describes the changes required in your application. Table 1-1. Comparison of the DDN R1 and DDP-PPC 6R1 TCP/IP Interface DDN R1 TCP/IP passes an open-id indication to the application after a passive open is issued. The application then loops, waiting for an open- indication to be returned. The host name field in the open packet is 24 characters long. An ASCII dotted-decimal local internet address is returned on an open-id. An ASCII dotted-decimal remote internet address is returned on an open-indication. DDP-PPC 6R1 The open-id is now returned to the user when an open indication arrives for the TSU. Therefore, the application must now loop waiting for the open-id after issuing a passive open. The host name field in the open packet has been increased to 255 characters to support domain names. (A domain name specifies the logical internet name whereas the host name is specified in internet physical address format.) Two fields have been added to the data packet: DDN-DOMAIN-HOST-INFO (contains the domain name) DDN-DOMAIN-HOST-LENGTH (contains the length of the domain name) DDP-PPC requests the domain name resolver to determine if the local or remote internet address has an associated domain name. If there is an associated domain name and the receive-event is an open-id, the user receives the local internet address and the local domain name. If there is an associated domain name and the receive-event is an open-indication, the user receives the remote internet address and the remote domain name. Current applications can therefore continue to function, and new ones can opt to use the associated domain name. (Current applications must recompile their programs to pick up the new data and open packet sizes.) continued 1v v100

21 Migration from DDN R1 to DDP-PPC 6R1 and Higher Table 1-1. Comparison of the DDN R1 and DDP-PPC 6R1 TCP/IP Interface (cont.) DDN R1 Since the GASIF interface sends TCP/IP data over a DCA session, errors are returned as data on a subsequent receive function. DDP-PPC 6R1 Errors are returned both when the function is issued and on the subsequent receive function. There are also additional error codes and some error codes are different than before. These are documented in the DDP-PPC/DDP-FJT Messages Reference Manual and returned to the application as received by DDP-PPC v100 1v5

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23 Section 2 Procedural Overview 2.1. DDP-PPC COBOL Program Structure Though DDP-PPC COBOL programs are similar to conventional programs, certain additional features are required. For example, you must: $ Include information packets and any other necessary working-storage areas in the data division of your program $ Use the COBOL COPY verb to copy verbs and function calls into the procedure division The following example shows the DDP-PPC COBOL program structure. The WORKING-STORAGE SECTION and PROCEDURE DIVISION in the example are unique to a DDP-PPC program. DDP Cobol Program Structure v100 2v1

24 DDP-PPC COBOL Program Structure 2v v100

25 Copying Information Packets 2.2. Copying Information Packets The working-storage section of the data division supplies DDP-PPC with the information needed to control data transfer between programs. This section contains 01-, 02-, 04-, and 88-level data description items in information packet formats. These packets correspond to the USING clause parameters of the DDP-PPC function calls discussed in Section Using the COBOL COPY DDN-PKTS Statement You use information packets to supply the data transfer control information. These packets are constructed for you using standard data descriptions. Copy these packets into your working-storage section from the COBOL copy library using the COPY DDN-PKTS statement in the procedure division of the program. (See 2.3.) The COPY statements place all the necessary data descriptions into your working-storage section when the program is compiled Sample Information Packets Produced from Copy Verbs The following example shows the information packets produced by copying DDN-PKTS into the working-storage section of a DDP-PPC application program. All the fields and parameters forming the information packets are described in detail with the related function calls in Section Sample Initialization Packets The DDP-PPC TCP/IP packets contain several fields that are not required each time that you issue a function. Each command packet has an associated initialization packet that you can use to clear unused fields before specifying any parameters and issuing a function call. You can tell DDP-PPC TCP/IP to ignore specific fields by: $ Setting them to a value, usually spaces or zeroes, on a field-by-field basis $ Initializing the entire packet and then resetting specific fields to the desired values These initialization packets are shown in the following example. Initialization Packets v100 2v3

26 Copying Information Packets 2v v100

27 Copying Information Packets v100 2v5

28 Copying Information Packets Additional Working-Storage Items You also use the working-storage section to define message areas and to store error messages. These areas and values are specific to your program and are not supplied through COPY verb statements. You must define a message buffer area. All program-to-program commands reference this area to transfer data. The maximum buffer size is 8232 characters. See 4.3 for a discussion on alternative ways to define this area. Example: Depending on your application, optionally include: $ Storage areas to hold conversation-id and status information supplied by DDP-PPC $ The name of the destination host computer on which the destination program resides (the program with which you are going to have a conversation) $ Offset and text length values to define your data messages $ Data messages and error messages 2v v100

29 COBOL Verbs and Function Calls 2.3. COBOL Verbs and Function Calls Application programs use conventional COBOL verbs for input/output data transfers and procedure division manipulations. They also use conventional verbs to set information fields in the working-storage section information packets. See Figure 2-1. Data Files COBOL I/O Verb COBOL Application Program DDP-PPC TCP/IP COBOL Function Call Status Data TCP/IP COBOL Interface Element DDP-PPC CMS TCP/IP Network Figure 2-1. COBOL Verbs and Function Calls Function Calls Special function calls are used for DDP-PPC applications. Use these function calls to: $ Enter the COBOL applications interface element $ Pass control information that is in your program $ Issue requests to DDP-PPC. Figure 2-2 shows how a function call references information packets. In this case, it shows how to use a standard COBOL MOVE verb to set an information packet field before issuing the call v100 2v7

30 COBOL Verbs and Function Calls DATA DIVISION... WORKING-STORAGE SECTION. 01 DDN-STATUS-PKT DDN-SIGNON-PKT. 02 DDN-PROGRAM-NAME DDN-OPEN-PKT DDN-RECEIVE-PKT DDN-DATA-PKT.... PROCEDURE DIVISION. MOVE 'MYPROGRAM' TO DDN-PROGRAM-NAME. CALL 'DDN$SIGNON' USING DDN-STATUS-PKT, DDN-SIGNON-PKT. Figure 2-2. Referencing Information Packets through Function Call USING Clauses The format for a function call is: where: function Is the name of the DDP-PPC function call requested by your application program. USING Is the clause that references information packets or buffer areas in your working-storage section. Parameters in the USING list are positional. You must code them in the order shown in each function call. param Is the name of the information packet or buffer area in your working-storage section. Function call statements always contain USING clauses that reference information packets or buffer areas contained in your working-storage section. (See Table 3-1.) The information packets consist of control information and data needed for program communications. The buffer areas are used to pass data between DDP-PPC and your program. 2v v100

31 COBOL Verbs and Function Calls After processing a function call, DDP-PPC returns both a general, a detailed status code, and a specific error code. The general status code, or class code, gives a classification value. The detailed status code gives an expanded description of the error that occurred. The specific error code provides additional error information, such as the error code DDP-PPC received from CMS. These codes are explained in the DDP-PPC/DDP-FJT Messages Reference Manual COPY Verbs Use the COPY verb in the procedure division of the application program whenever you want to issue a function call. The expansion in your program ensures the correct order of the operands in the call. The format for a COPY statement is: where: text-name Is the name of the function or information packet. This is an example of a COPY verb used to produce a DDP-PPC function call with its information packets referenced: This produces: ZDDDDDDDDDD? Initializing Packet Field Values The DDP-PPC packets contain several fields that you do not require each time that you issue a function. You can tell DDP-PPC to ignore specific fields by: $ Setting them to a value, usually spaces or zeros, on a field-by-field basis $ Initializing the entire packet and then resetting specific fields to the desired values To initialize the packet and reset specific fields, perform the following steps: 1. Initialize or reinitialize all the allocated packets using a supplied set of packets that are pre-set to the required DDPvPPC initialization values. You can include this set of packets in you program by issuing the following statement: v100 2v9

32 COBOL Verbs and Function Calls 2. Set the default values for the DDP-PPC control packets by initializing individual packets: 3. The packet to be used in the function can then be initialized by assigning the initialization packet to it. For example, the DDN-OPEN-PKT can be initialized by coding the following in the main program: As a general practice, after you have moved the desired values into their respective fields, issued a command, and control has returned for the next operation, you should reinitialize all unused fields before issuing a different command. Without reinitialization, the command may generate an error message or produce unexpected results. 2v v100

33 Section 3 Using DDP-PPC TCP/IP Function Calls This section describes the usage of each COBOL COPY verb with its associated information packets. Table 3-1 lists the COPY verbs, function calls, and information packets in the order you would use the commands in a typical program COBOL COPY Verbs and Function Calls You can use COBOL COPY verbs or code your own COBOL function calls to issue program-to-program commands from your COBOL program. You can direct these commands to the same host or to any remote host defined in the network. When you use a COBOL COPY verbs, the associated function call referencing the required information packets replaces the COPY verb when the program is compiled. You can code the function call yourself, but you must then supply the information packet names in the correct sequential order shown in Table 3-1. See 2.2 and 2.3 for a discussion on how to use function calls, information packets, and COPY verbs. Unused fields should be cleared before specifying any parameters and issuing a function call. You can use the initialization packets provided by DDP-PPC to initialize the fields. Table 3-1. Copy Verbs and Associated Function Calls and Information Packets Function COPY Verb Function Call Information Packets Referenced in USING Clause by COPY Verb/Function Attach an application to DDP-PPC Open a conversation with a host or wait for another host to open a conversation COPY DDN-SIGNON DDN$SIGNON DDN-STATUS-PKT DDN-SIGNON-PKT COPY DDN-OPEN DDN$OPEN DDN-STATUS-PKT DDN-MSG-BUFFER DDN-DATA-PKT DDN-OPEN-PKT Send a message COPY DDN-SEND DDN$SEND DDN-STATUS-PKT DDN-MSG-BUFFER DDN-DATA-PKT continued v100 3v1