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Installation and Reference Guide ClearConnect 1.3

Chapter 2: Introducing ClearConnect

Chapter 2

This chapter provides an overview of ClearConnect and DRDA.
It includes the following topics:

• General Information
• What is ClearConnect?
• What is DRDA?
• How ClearConnect Works with DRDA
• Features of ClearConnect
• Product Prerequisites
• Restrictions
• Getting Ready for Setup

General Information

ClearConnect provides a seamless, direct attachment from Open Database Connectivity (ODBC) client applications to DB2 databases. ClearConnect allows ODBC applications to query and update DB2 databases from any client machine that runs it. This ability expands the scope of databases that ODBC applications can operate against, and provides a way for clients connected on a LAN or WAN to access DB2 databases.

When used with third party products, such as InfoHub, ClearConnect can access and update nonrelational "legacy" data on IBM mainframes, for example, ADABAS, IDMS, CA-DATACOM, VSAM, and IMS(TM) DL/1 databases. ClearConnect software allows users to access a wide range of relational and nonrelational data from a single ODBC driver.

ClearConnect runs on the following Microsoft platforms:

• Windows NT
• Windows 95
• Windows 3.x
• Windows for Workgroups

The following figure shows the types of client/server configurations that ClearConnect supports.

Figure 2-1: Supported client/server configurations

What is ClearConnect?

Using the IBM-defined Distributed Relational Database Architecture (DRDA) protocol, the ClearConnect software product provides a connection from an ODBC application, such as PowerBuilder, Access, or Excel, to an IBM DATABASE 2 (DB2) relational database management system, or to any other certified DRDA application server, such as the InfoHub server. ClearConnect is designed for DB2 databases and application servers that are configured for DRDA functionality.

ClearConnect is composed of two layers of software:

• An upper layer that processes ODBC function calls
• A lower layer called the application requester, which provides encoding and decoding of DRDA requests and replies over a network

For a list of the ODBC commands and datatypes that ClearConnect supports, see Appendix A, "ODBC SQL Commands and Datatype Conversion."

What is DRDA?

DRDA is an IBM application-level protocol that transfers database and stored procedure requests and replies between clients and servers. It describes the form and content of the following:

• Client login information
• Client requests (SQL requests and stored procedure requests)
• Server replies in the form of row and column information that is returned as result set (reply) data
• Error information and status

DRDA supports client/server communication between the following:

• Workstations and mainframes
• Mainframes and other mainframes
• Workstations and other workstations

Over 14 major vendors support DRDA in their products, making it a multi-vendor solution for client/server database access.

For more information about DRDA, see the references listed in "Related Documents".

How ClearConnect Works with DRDA

ClearConnect is a middleware software component that is ODBC-compliant. Using the DRDA protocol, ClearConnect allows desktop applications to access host-based and minicomputer-based DB2 relational databases.

This section explains:

• Flow of SQL requests
• Connecting clients to targets

  Note: ClearConnect operates as a shared system library (a DLL on Windows).

Flow of SQL Requests

The following figure shows how SQL requests travel from the client ODBC application through ClearConnect for execution. It also shows the result data returns from the database server to the requesting client.

Figure 2-2: Process flow of requests and returned results

The steps that ClearConnect performs in the preceding figure are as follows:

1. ClearConnect accepts ODBC API calls from ODBC applications or tools, and then creates a DRDA request by converting them into DRDA SQL requests and DRDA parameters
   (called "parms" in Figure 2-2). Then, it sends these requests to the target database.

2. ClearConnect executes the client's associated SQL statement or stored procedure request against the target DBMS.

3. ClearConnect retrieves the results from the target DBMS.

4. ClearConnect converts the returned datatypes from the target DBMS into a datatype format acceptable to the ODBC client, for example, EBCDIC to ASCII, big endian 370 to little endian 80x86 integers, and so on.

5. ClearConnect returns the results of the SQL statement or stored procedure to the requesting ODBC application.

Connecting Clients to Targets

To connect a client to its target, the distributed client/server database environment uses two levels of configuration, shown in the following table:

Table 2-1: Configuration levels for distributed client/server database

Type of configuration	Description
Client-to-server database configuration information	Carries information about the target database the client wants to connect to, such as what levels of locking (cursor stability, repeatable read, and so forth) are wanted.
Networking configuration	Physically connects the client machines to the server machines. This specifies the SNA or TCP/IP networking information that allows the client and server machines to communicate with each other over a LAN- or WAN-based network. This information is usually the Host Names (TCP/IP) of the machines or the LU Names (SNA) that identify the machines.

Using information from these two configuration levels, ClearConnect and DRDA can connect client PCs to the target server, as shown in the following figure:

Figure 2-3: ClearConnect and DRDA connecting clients to target

Note: IBM refers to the target DBMS server as the Remote Location Name (RDB_NAME). ODBC application programs use these logical unit (LU) names of the DRDA database servers to connect to the target database system.

As shown Figure 2-3, client/server configuration information allows the client to communicate with the servers.
The client issues a SQLConnect request to a specific ODBC data source, which is converted to a DB2 Location Name. Then, DRDA routes the request to the correct database server with that logical name. In reality, the preceding conceptual system must be built on top of a computer network and the networking software that ties the various machines together.

The networking configuration information allows clients and servers to communicate. The following figure shows the client/server networking components for an SNA environment.

Figure 2-4: Client/server components in an SNA environment

The following figure shows the database clients and server with their associated networking components for a TCP/IP environment.

Figure 2-5: Client/server components in a TCP/IP Environment

Features of ClearConnect

ClearConnect provides the following features:

• Support for the latest DRDA Level 3 features, including stored procedure support to DB2/MVS 5.1 and DB2 Universal Server 5.0.
• ODBC 2.0 and 2.5 support, allowing operation with hundreds of ODBC applications and 4GL GUI tools, such as Power Builder, Access, Impromptu, Forest and Trees, Excel, and Visual Basic.
• Support for 16-bit Windows clients (Windows 3.1, Windows for Workgroups) and 32-bit Windows clients (Windows 95, Windows NT).
• Support for the following client platforms:
  • Windows NT 3.51 and 4.0
  • Windows 3.1
  • Windows 95
• Allows access to mainframe (MVS) and minicomputer (AS/400, AIX/6000) databases directly from the client.
• Provides plug-and-play support for the following DRDA server platforms:
  • Mainframe, including DB2/MVS 3.1, 4.1, and 5.1
  • AS/400
  • Windows NT, AIX, Solaris, HP-UX, and OS/2 using DB2 version 2.1 or later
  • InfoHub on MVS
• Provides support for concurrent access to multiple servers.
  For example, an ODBC application can open one connection to DB2/MVS and another to DB2/6000; then, it can access data from both systems simultaneously.
• Installs quickly and easily, using standard ODBC administrator GUI tools.
• Provides TCP/IP support for DRDA platforms that are enabled for DRDA Level 3 TCP/IP support.
• Requires no special software on the IBM mainframe and interoperates with the standard DB2/DDF software supplied with DB2/MVS.
• Supports the DRDA database interoperability standard.
• Provides ODBC and X/Open CLI support for many existing ODBC applications and tools.
• Provides high throughput to the target database, delivering high performance while it supports the ODBC API.

Product Prerequisites

Two major requirements exist for the ClearConnect product:

• Communications software
• Client platform

The following subsections describe each requirement.

Communications Software

ClearConnect supports the following communications software:

• SNA LU6.2 is the only supported protocol for pre-version 5.1 DB2/MVS databases, SQL/DS, and AS/400 databases.
• SNA LU6.2 or TCP/IP is the supported protocol for version 5.1 DB2/MVS databases and InfoHub servers.

  Note: If DB2/MVS is used with SNA, VTAM version 3, release 3 or later is required.

Client Platforms

The following subsections describe the requirements for various client platforms.

Windows 3.1 or Windows for Workgroups Clients

Clients based on Windows 3.1 or Windows for Workgroups require a minimum of the following:

• Windows 3.1 or Windows for Workgroups version 3.11 or later
• 2-8 MB main memory (RAM)
• 10 MB of hard disk storage
• A network connection between client workstations and the DRDA server. The network connection can be one of the following:
  • LAN (Token-Ring, Ethernet, FDDI)
  • WAN (SDLC or PPP)
  • X.25
  • S/370 channel
• Communications protocol:
  • If you are using SNA LU 6.2, a Windows NT system running SNA Server 2.11 or later is required. For improved security, use Windows NT SNA Server 3.0.

    Install the SNA Server client software on Windows 3.1 and Windows for Workgroup clients by attaching to SNA Server, which resides on a Windows NT system. Then, Windows 3.1 and Windows for Workgroup clients can communicate with the mainframe.

  • If you use TCP/IP, a WinSock 1.1-compliant TCP/IP driver for Windows 3.1 or Windows for Workgroups is required.
• Database server software, such as:
  • DB2/MVS version 3.1 or later
  • DB2/6000 version 2.1 or later
  • DB2/NT version 2.1 or later
  • InfoHub

Windows 95 Clients

Windows 95-based clients require a minimum of the following:

• Windows 95
• 8-16 MB main memory (RAM)
• 10 MB of hard disk storage
• One of the following network connections between the client workstations and the DRDA server:
  • LAN (Token-Ring, Ethernet, FDDI)
  • WAN (SDLC or PPP)
  • X.25
  • S/370 channel
• If you use SNA LU6.2, a Windows NT system running SNA Server 2.11 or later is required. For improved security, use Windows NT SNA Server 3.0.

  Install the SNA Server client software on Windows 95 clients by attaching to SNA Server, which resides on a Windows NT system. Then, Windows 95 clients can communicate with the mainframe.

• Database server software, such as the following:
  • DB2/MVS version 3.1 or later
  • DB2/6000 version 2.1 or later
  • DB2/NT version 2.1 or later
  • InfoHub

Windows NT Clients

Windows NT-based clients require a minimum of the following:

• One of the following:
  • Windows NT Server 3.50
  • Windows NT Workstation 3.50 or later
• 16-32 MB main memory (RAM)
• 10 MB of hard disk storage
• A network connection between the client workstations and the DRDA server. The network connection can be one of the following:
  • LAN (Token-Ring, Ethernet, or FDDI)
  • WAN (SDLC or PPP)
  • X.25
  • S/370 channel
• If you use SNA LU 6.2, SNA Server 2.11 or later is required.
  For improved security, use Windows NT SNA Server 3.0.

  If SNA Server is running on a different Windows NT machine, you must install the SNA client software on this machine to communicate with the mainframe.

• Database server software, such as:
  • DB2/MVS version 3.1 or later
  • DB2/6000 version 2.1 or later
  • DB2/NT version 2.1 or later
  • InfoHub

Restrictions

ClearConnect support has restrictions that are consistent with other DRDA Application Requester (AR) implementations, as follows:

• ClearConnect does not support two-phase commits between itself and the DRDA servers in this release. Most of the workstation versions of SNA do not have the "hooks" needed to perform SNA two-phase commits.
• DB2 stored procedure support requires DB2/MVS 4.1, AS/400 Release 3.6, or DB2/Common Server 2.1 or later. These versions only support input and output parameters, and do not allow one or more result sets.
• Full stored procedure support, including multiple result sets, is currently available when using Platinum InfoHub/MVS servers. ClearConnect also supports stored procedure multiple result sets with DB2 Version 5.
• The TCP/IP support that IBM supplies with its existing DB2/Common Server 2.1 products does not use standard DRDA protocols. Instead, the TCP/IP support uses private, undocumented protocols that do not interoperate with the TCP/IP support defined by DRDA (Level 3). To use DRDA with TCP/IP to DB2/Common Server, Version 5 of the IBM product is required.
• Only APPC (SNA) can be used between ClearConnect and IBM DB2/VM and DB2/VSE, and with other pre-Version 5 DB2 systems.
• ClearConnect allows a client to issue DB2-specific SQL to the target DBMS and does not monitor the SQL dialect used. This allows transparent access to all features of the target DBMS. The disadvantage is that these ODBC applications are non-portable and work only with the specific target DBMS.
• DRDA does not currently support "blob" datatypes, such as TEXT and IMAGE. As a result, ClearConnect does not transfer blob information between DRDA clients and TEXT and IMAGE datatypes that are greater than 32 K bytes.

Getting Ready for Setup

Before you begin, be sure to copy the Installation Worksheet pages from Chapter 3, "Installation Guidelines and Quick Start Steps." When completed, the Installation Worksheet gives you, your DB2 database administrator (DBA), and your network administrator the list of parameters needed to install ClearConnect.

Note: Be sure to allow time to research information for the Installation Worksheet.