Peer into the back offices of most large companies and you’ll probably find at least one mainframe or minicomputer running business-critical applications. Many midsize and smaller companies are in the same position. In many ways, the smaller the company, the harder it is to move away from those mainframes and minis to other solutions. The cost of replacement servers is a factor, but porting applications and data is often a much more formidable barrier to such a transition. That’s where Microsoft’s Host Integration Server (HIS) comes into the picture.

HIS is a follow-up product to Microsoft’s SNA Server. It comprises a wide range of tools and services that gives clients transparent access to data on mainframes, AS/400, UNIX, Windows 2000, and Windows NT servers. This means that you can continue to use your back-end servers and applications but provide access to them in new ways, including Web-based interfaces. I’m going to take you on a tour of the components and features of HIS.

HIS integrates legacy systems with newer networks
In a nutshell, HIS enables you to integrate legacy host systems with client/server and Web-based information networks. One piece of the HIS integration puzzle is the ability of clients to access data on back-end legacy servers through Windows 2000 and Windows .NET servers, as well as through Windows-based 3270 and 5250 client capabilities included with the product. You can also use other third-party clients to access the servers, even when access is funneled through HIS servers.

Access isn’t limited to just applications and data—clients can easily access files and printers on the back-end systems, too. HIS is very scalable, supporting up to 30,000 concurrent host sessions per server. It improves reliability with support for Microsoft Message Queue (MSMQ) and Component Object Model (COM+). Support for Microsoft Application Center, Network Load Balancing, and other failover technologies means reliability and high availability for clients.

In addition to facilitating client access through emulation clients, HIS enables you to provide client access through custom applications you develop in-house, including Web-based applications. HIS provides built-in data-access capabilities to retrieve data from SQL Server and DB2, and flat-file data on mainframe, AS/400, UNIX, Windows 2000, Windows .NET, and Windows NT servers. HIS also provides drag-and-drop support for IBM’s CICS and IMS, enabling your developers to more easily integrate applications that use Microsoft Transaction Server and COM+ with these host services.

HIS also offers some handy security-related features. It lets clients log on simultaneously to Windows domains and back-end host systems with a single sign-on. In addition, HIS allows administrators to map user account information on Windows domains to the user’s credentials on the back-end host. This synchronization can significantly reduce the amount of time needed for account administration. To provide security for remote users, HIS supports virtual private networking, enabling VPN connections between clients and hosts.

Let’s take a look at the components of HIS so you can begin to understand how they might fit into your enterprise.

HIS components and services
HIS includes several services, each of which supports connectivity and access in a particular area. These components and services fall into four main categories:

  • SNA network connectivity: HIS builds on Microsoft’s SNA Server to provide the network services needed to connect Windows 2000/.NET Servers and multiplatform clients to mainframe and minicomputer servers. HIS acts as an SNA gateway, performing protocol conversion between client systems and host servers. Using an SNA gateway in this way means you don’t need to install or manage SNA protocols on the clients or add services to the host servers to accommodate the clients’ network capabilities and protocols.
  • Data integration: The data integration components in HIS lets server- and client-based applications access data stored on the host servers. HIS provides access to relational and nonrelational data on target host systems through a variety of mechanisms, including ODBC, OLE DB, and COM.
  • Application integration: These components provide the link between Web- and Windows-based applications on client systems and applications on the host systems. HIS supports both synchronous and asynchronous transactions.
  • HIS management: These components provide the administrative hooks into the components of HIS and include such tools as the Microsoft Management Console (MMC) for managing HIS, command-line management utilities, scripting tools, and Web-based administration tools. These tools give you flexibility in managing HIS directly, from remote stations, or through administration scripts and batch files.

SNA connectivity
Obviously, your servers—and ultimately the clients—need a connection to the host servers. Prior to Windows 2000, Microsoft operating systems used NetBIOS as the primary network mechanism. That changed with Windows 2000, XP, and .NET, which all use TCP/IP as the default protocol.

HIS operates as an SNA gateway between the clients and the host servers, providing protocol conversion for the clients. In most cases, this eliminates the need to install SNA protocols on the clients or additional network software on the host servers. For example, Windows 98 clients using TCP/IP as their only protocol could access data and shared resources on IBM System/390 and AS/400 servers through the HIS gateway without major configuration changes. By supporting standard protocols such as TCP/IP, HIS also makes it possible for non-Windows platforms to access the back-end servers.

The SNA architecture built into HIS allows it to communicate with the host servers, which in turn makes it possible for HIS to provide status information for connections and services to other HIS servers and clients. The server builds the list of available servers, links, logical units (LUs), and invokable telecommunication programs (TPs) available on the host servers. It stores the information locally and also shares it with other HIS servers. When a client requests a host resource, the HIS server uses this information to determine where the requested resource resides and then provides the client with a list of servers that offer the resource. HIS also provides the client with the LU for the resource.

Clients use a similar set of components to access HIS and the services it offers. HIS directly supports Windows 2000, Windows .NET, Windows XP, Windows NT, Windows 9x, Windows 3.x, MS-DOS, and OS/2 clients. You can add support for Macintosh, UNIX, and VMS clients by adding third-party client software.

HIS supports several server-to-server network protocols, including direct channel attachment, DLC 802.2, SDLC, and X.25. Support for these protocols allows HIS to connect to a wide range of back-end systems. HIS supports a range of LAN connection media, including Ethernet, Token Ring, and Fiber Distributed Data, as well as coax connections. HIS also supports TCP/IP, IPX/SPX, Microsoft Networking (named pipes), and AppleTalk for communication between HIS clients and HIS servers, as well as TCP/IP and IPX/SPX for intercommunication between HIS servers.

HIS includes terminal emulation support with basic 3270 and 5250 emulation. However, Microsoft intends for you to use the built-in terminal emulation mainly for testing and configuration. It recommends that you obtain a third-party emulation package for the clients. HIS also supports 3270 and 5250 emulation directly over TCP/IP, eliminating the need for the client to host any part of the SNA protocol stack.

Data integration
The data integration components in HIS enable clients to access data stored on mainframe and AS/400 servers. HIS data integration supports relational database access, record file access, file transfer, and AS/400 data queue access. HIS relies on IBM’s host-based Distributed Data Management Architecture (DDM) to implement communication between HIS servers and host servers. It supports DDM for OS/390, AS/400, RS/6000, and AS/36.

Most commonly, the host server uses IBM’s DB2 as the relational database engine, whether integrated as part of the host operating system or deployed via RDBMS. HIS supports connectivity to DB2-based host databases through Open Database Connectivity (ODBC) and Object Linking and Embedding Database (OLE DB). It supports ODBC through either a back-end ODBC driver or a front-end application. Microsoft provides two mechanisms to access DB2 through HIS: the Microsoft ODBC Driver for DB2 and the Microsoft OLE DB Provider for DB2. These run on the HIS server(s) and enable applications and Web services to access the data on the host server through the HIS connection.

HIS also supports access to data stored in VSAM files, partitioned datasets, and AS/400 files. It accomplishes this support through an OLE DB provider for AS/400 and another OLE DB provider for VSAM. The AS/400 provider offers record-level access to nonkeyed and keyed physical files with external record descriptions and to logical files with external record descriptions. The AS/400 provider enables mapping of AS/400 data types to OLE DB data types through the use of a Host Column Description file that defines the format for the target flat data file. The VSAM provider supports most types of mainframe VSAM files, including Sequential Access Method (SAM), Virtual Storage Access Method (VSAM), and basic Partitioned Access Method data sets. These OLE DB providers make it possible for your developers to create front-end and Web-based applications that access this nonrelational data.

You’ll also find support for file transfer in HIS, including Host File Transfer, APPC File Transfer Protocol (AFTP), and AS/400 Shared Folders. The Host File Transfer utility is provided through an ActiveX control; it enables application developers to access the same VSAM data types that are supported by the OLE DB provider, but it’s optimized for uploading and downloading entire data sets. Host File Transfer also supports AS/400 and System 36. APPC is similar in function to the venerable FTP utility, but it’s designed for SNA systems. You can install the AFTP software on the HIS server(s) or client systems.

The AS/400 Shared Folders feature included with HIS enables an administrator to share a folder on an AS/400 host server as if it were local to the HIS server. To the client, the folder appears in the list of shared resources for that HIS server and can be accessed in the same manner as other shared resources that really are local to the HIS server. This pass-through sharing means that clients can access the shared folders on the AS/400 without any additional client software.

Application integration
The application integration components in HIS let developers create solutions that tie Windows-based applications to applications running on the host servers. HIS includes a component called the COM Transaction Integrator, or COMTI, which enables developers to create applications that allow CICS and IMS applications running on the host servers to participate in COM-based transactions.

COMTI does this by creating a wrapper for back-end CIS and IMS applications that makes them function essentially as a COM component during application execution. In effect, COMTI serves as a proxy between the standard COM+ and MTS applications running on the client or Windows server side and the target CIS or IMS application running on the host server. COMTI uses Distributed COM (DCOM) to provide communication between HIS and the COM components, with HIS handling the SNA protocol conversion.

COMTI and COM are useful when the client application needs confirmation that the transaction has been completed. With some applications, however, developers prefer to rely on other methods to ensure transactional integrity and completion. The MSMQ, for example, provides that function. Like other messaging software, MSMQ serves as a proxy of sorts for the client application, placing the data in a queue and then taking on the responsibility of completing the transaction on behalf of the client.

Although MSMQ is the messaging middleware provided for Windows platforms, most host servers use IBM’s MQSeries. To facilitate transaction processing between Windows platforms and host servers, HIS includes a component called the MSMQ-MQSeries Bridge. The bridge sits between MSMQ and MQSeries, translating messages to and from the two to provide bidirectional message transfer.

HIS server and client management
The fourth category of services and components provided with HIS falls under the general heading of administration. This includes the tools you use to configure and manage HIS, client software, and the components that integrate HIS with Active Directory and tie Windows-based security to host-based security for account synchronization and management.

The primary tool for configuring and managing HIS is the SNA Manager MMC. You use the console to define link services, connection types, LUs, LU pools, user groups, client workstations, and resources. In addition, HIS provides command-line tools you can use to manage HIS servers and resources. You can use the Windows Scripting Host provided with Windows 2000 and Windows NT, as well as batch programs that utilize the command-line tools, to manage HIS resources without the MMC. You can also create custom applications that use Windows Management Instrumentation (WMI) to provide Web-based management for remote servers. For situations where you need remote access to SNA host servers, SNA Remote Access Services (SNARAS) provides integration between Windows RAS and your SNA links. This means you can connect to remote SNA servers across SNA links.

In terms of client support, HIS provides a handful of client tools. The HIS CD contains client software for Windows 98, Windows 3.x, Windows NT Workstation, and Windows 2000 Professional clients. The client software includes the base client, API support, DB providers, and terminal emulators. Which components you install will depend on whether you’re also using third-party client software. If the third-party software provides emulation and other features, you can generally get by with installing just the base client. You can install the client software using several methods, including local CD, network share point, and SMS. HIS 2000 also provides for Web-based client installation, enabling clients to install the software simply by clicking a link on a Web page. The Web-based option gives the user the option of installing just the base client, the full client and the 3270 emulator, or the full client and the 5250 emulator.

Putting HIS to work
HIS doesn’t provide every possible feature you might need in a host interoperability solution, but out of the box, it provides an excellent level of core components and client services that enable immediate client access to host-based data. Through programming, you can extend client access and provide additional data access mechanisms, such as Web-based access. You can also combine HIS with third-party client and server solutions to broaden its capabilities.

In short, if you have mainframe or minicomputer systems inhabiting your server rooms and need to tie your Windows-based servers and multiplatform clients into them, HIS is certainly worth a look. You can decrease administrative overhead by simplifying account management and application development. What’s more, by providing clients with a Windows- or Web-based data access solution to your host systems, you’ll decrease support costs. The more your users can stay in a familiar realm, the less likely they are to have problems your IT staff must address. Best of all, you won’t need a major capital investment to replace existing servers and applications.