Networking concepts and terminology

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This topic presents terminology used when referring to Model 204 intersystem communication. Because the meaning of networking terms could be different in a Model 204 context, Technical Support recommends that all connectivity system administrators read this topic.

Basic networking terms and concepts

In this topic, a computer network is defined as a collection of nodes, connected at the software level by a communication interface.

Different types of nodes exist on a network: application nodes, terminal nodes, printer nodes, and so on. When the term "node" is used in this topic, however, it refers to an application node: the point of connection to the network for some system that supports application programs.

Some examples of communication interfaces are:

  • Virtual Telecommunication Access Method (VTAM)
  • Transmission Control Protocol/Internet Protocol (TCP/IP)

The following figure shows a hypothetical network that consists of three nodes. The software communication interface used is TCP/IP.

The transactions originate from the client nodes — PCs and workstations (nodes A, B, and C) — that request information from the server node, where the Model 204 SQL process runs.

Network transactions

SQL Connect Guide fig 1-1.gif

Figure description

Essential elements shown in the previous figure are:

  • Exchange of data between two application programs at different nodes is referred to as a conversation.
  • Two programs that converse are referred to as conversation partners.
  • Client nodes — the PCs and the workstations — are also end users. An end user is defined as a user connected to a Model 204 terminal thread.
  • For each end user in a Model 204 TCP/IP (Horizon) network, its operation is transparent.

TCP/IP concepts and terminology

The Transmission Control Protocol/Internet Protocol (TCP/IP) is designed for building network interconnections.


The transmission control protocol (TCP) controls the transfer of the data. The TCP layer provides logical connections between pairs of processes. In TCP, a connection is defined by a pair of sockets, processes that are exchanging information, and a conversation is the communication link between the two processes. TCP provides reliability in data transmission and controls the data flow.


The internet protocol (IP) provides the routing mechanism for the data. The internet protocol creates a virtual network view and acts as a layer to hide the underlying physical network.

The IP address is a 32-bit address, usually represented in dotted decimal form. The internet protocol uses an IP address to specify two logical addresses:

  • Network address represents the physical network within the internet
  • Local address specifies an individual host within the physical network


A port is an identifier used by TCP/IP to distinguish one client node from another in a network connecting many client nodes to a single host (or server).

Identifying Model 204 to TCP/IP

In setting up a client node for the Model 204 TCP/IP (Horizon) network, you provide an IP address and port number combination to identify Model 204. This example shows a valid IP address/port number combination:

where: Is the dotted decimal notation address
1003 Is the port number


A TCP/IP connection transports requests and responses between the client nodes and the server node.

A conversation occurs over a connection. In the SQL connectivity topics, descriptions of Model 204 TCP/IP (Horizon) use conversation and connection interchangeably, because a connection is dropped when a conversation ends.

The Model 204 server process (CCARSQL) receives information from the client nodes, completes the specified action, and returns data to the clients.

Overview of Model 204 SQL processing

This section briefly reviews the components involved in Model 204 SQL processing. SQL processing transport methods are described in SQL processing transport methods. For a more complete discussion of all SQL processing components and related concepts, see SQL Server overview.

SQL Server

Client/server architecture allows the Model 204 to act as an SQL Server on the host machine, to service clients' TCP/IP. The SQL Server invokes Model 204 database management system (DBMS) operations, and provides a combination of Model 204 and SQL database functionality. Its main components are:

SQL Engine Compiles SQL syntax strings, checks SQL semantics, optimizes database access, generates code to accomplish SQL requests, and executes the generated code. Each SQL statement generates data, status information, or both for the requesting application.
SQL Server Front End (SSFE) Serves as the access layer to the SQL Engine, accepting client request packets, processing each packet's requests for the SQL Engine, and returning the SQL processing result to the client.

The Model 204 SQL Server provides full SQL processing in one of these locations:

  • Address space (z/OS)
  • Virtual machine (VM)
  • Partition (VSE)

SQL Server associated software

The SQL Server works in conjunction with the following Model 204 software:

SQL catalog CCACAT is the Model 204 system file that houses the SQL catalog information for Model 204 files defined with SQL Data Definition Language (DDL).
SQL communications interface Receives SQL requests from TCP/IP and passes them to the SQL Server Front End (SSFE). The interface receives result packets from the SSFE and routes them back to the client. This Model 204 module is used only for SQL processing.
SQL Client Front End (SCFE) Groups and sends client requests, and receives and distributes results to the client. The SCFE is platform independent.

SQL Server supporting tools

These Model 204 tools support SQL Server processing:

Table Specification facility (TSF) Model 204 subsystem (CCATSF) that provides an interactive, menu-driven facility for mapping existing Model 204 files to SQL tables and columns. The TSF is available on the mainframe only.
Catalog Reporting facility (CCACATREPT) Model 204 subsystem that provides a menu-driven facility for generating DDL from and reports of the SQL catalog contents. With the CCACATREPT, you can review your SQL object definitions, names, and privileges or use the DDL that it generates to repopulate the SQL catalog. CCACATREPT is available on the mainframe only.

SQL processing transport methods

Transport of the data between the SQL Server and its clients relies on the communication layer: Model 204 TCP/IP (Horizon). These interfaces, which define client to SQL Server connections, are described in this topic and shown in Model 204 SQL processing transport methods.

The figure includes the workstation clients that can be configured with the Connect Suite for Model 204 drivers. You can configure Model 204 z/OS, z/VM, or z/VSE TCP/IP connections to workstation clients.

Application program interfaces

Connect application programming interfaces are shown in the following figure as elements in the client configurations. Brief descriptions of these interfaces follow the figure.

Workstation clients can use the following 32-bit Connect Suite for Model 204 drivers, which lets you use dynamic SQL statements in any Windows application that uses Microsoft Open Database Connectivity (ODBC), JDBC, or .NET Framework function calls.

Model 204 SQL processing transport methods

SQL Connect Guide fig 1-2.gif

Model 204 TCP/IP (Horizon)

Model 204 contains a TCP/IP intersystem processing facility that enables Model 204 applications to participate in program-to-program processing through the Connect Suite using the TCP/IP type of connection.

Connect requires that Model 204 TCP/IP (Horizon) be installed and running on the mainframe serving as the host machine in your network.

For more information about Horizon, see the Horizon wiki topics.

Along with IBM/TCP-IP software on the mainframe, Model 204 TCP/IP (Horizon) supplies a connection to TCP/IP software on workstations.

Windows Sockets (winsocket) support

A socket is a function that makes it possible for an application to access a communications protocol. Windows provides such a function, a Windows Sockets (winsocket) connection.

The Connect Suite provides winsocket connection support, which lets you connect to Model 204 using Connect and a Windows TCP/IP package that supports winsocket calls.

Interface product to support Windows Sockets

To use Model 204 TCP/IP (Horizon), you need installed and running on your PC or workstation an interface product that supports Windows Sockets.

Other requirements

To complete the TCP/IP connection, you must also make sure that your system meets these requirements:

  • IBM/TCP-IP is running on the mainframe
  • PCs are able to "talk to" the mainframe

    Use the ping command to check the network connection and make sure that each PC and workstation is communicating with the mainframe.

Procedures for defining the network

DEFINE LINK, DEFINE PROCESS, and DEFINE PROCESSGROUP are the commands that you use to define the TCP/IP network to Model 204 for PCs and workstations.

For more information

For more information about installing Connect on a PC or workstation running Windows and TCP/IP software, see the Connect wiki pages.

Information to be gathered

To set up the Model 204 TCP/IP (Horizon) network, you might need to obtain information from the TCP/IP administrator. See Model 204 TCP/IP connection parameters.

Tasks summary

The following table summarizes the general tasks that you perform to set up Model 204 intersystem communication.

List of general tasks

Step Task See...
1. Include SQL-specific files in your online environment. SQL processing files
2. Set CCAIN parameters to support Model 204 SQL processing. CCAIN parameters to support Model 204 SQL processing
3. Size the CCATEMP file. CCATEMP file size
4. Define SQL and RCL IODEV threads. Defining SQL and RCL IODEV threads
5. Size the fixed server area and the variable server area. Server area sizing
6. Size SQL buffers. Setting initial sizes for SQL buffers
7. Review network definition entities. Making the necessary connections
8. Using Model 204 TCP/IP (Horizon), issue DEFINE commands for link, processgroup, and process. Link

See also