Microsoft's SNA gateway opens the way to new features and functions

Last November, Microsoft released the latest version of its Systems Network Architecture (SNA) gateway, SNA Server 3.0, which connects networked PCs with IBM AS/400s and mainframes. (To learn how SNA Server works, see the sidebar, "Interconnectivity with SNA Server ," page 96.) Version 3.0 is a major release that increases capabilities and adds to SNA Server's core feature set. In addition, Microsoft has improved several SNA Server features, including hot backup, dynamic load balancing, and multiple protocols, and has simplified setup and configuration.

New and Improved
One of SNA Server 3.0's biggest technical improvements is the increased client capacity. The previous limit of 2000 users and 10,000 sessions has increased to 5000 users and 15,000 sessions. This new limit makes SNA Server the highest-capacity SNA gateway available.

Among SNA Server 3.0's new functions, you'll find SNA Print Services, which provide server-based 5250 and 3270 printer emulation. SNA Print Services let host applications print on printers connected to the Windows NT server or attached NetWare servers.

SNA Server 3.0 uses RSA RC4 encryption to provide SNA data stream encryption between SNA Server and it's clients. Standard SNA and TCP/IP connections send 5250 and 3270 screens (including those with user ID and password) across the network in unencrypted, clear-text format. SNA Server 3.0 lets you encrypt these screens, which is important if you connect to a host across a public network such as the Internet.

SNA Server 3.0 adds several AS/400-specific functions that extend the role of the SNA gateway. For example, a single logon synchronizes passwords between SNA Server and the AS/400 host, thereby eliminating the need to log on multiple times to access the LAN and the AS/400. With this feature, users can change their password on the NT server or the AS/400, and SNA Server changes the password on the other system. (You need an ExecuSoft AS/400 add-on to send password changes made on the AS/400 to SNA Server--no matter what OS/400 release you use.)

Another new AS/400-specific feature is the shared folders gateway (SFG). Previous versions of SNA Server did not support shared folders (an AS/400 feature that lets you access AS/400 disk storage from a PC client). SNA Server 3.0 supports shared folders via the server. With this new feature, AS/400 shared folders appear as one or more drives on the NT server running SNA Server. All networked clients that can access the NT server running SNA Server can access AS/400 shared folders. The SFG is available for DOS, OS/2, Windows for Workgroups 3.11, Windows 3.1, Windows 95, and NT clients.

SNA Server's SFG uses NT Server security rather than AS/400 security to protect files in the SFG directory. SNA Server restricts the SFG to the old AS/400 QDLS file system. Unlike IBM's Client Access product, SNA Server 3.0 doesn't provide access to the new (V3R1) Integrated File System (IFS) root directory. This limitation prevents the SFG from accessing the same range of folders available to the direct AS/400 Client Access connections.

With version 3.0, SNA Server can provide AS/400 access via TN5250 without requiring AS/400 TCP/IP. A client system can connect to SNA Server via TN5250 and TCP/IP, and then SNA Server can use SNA to route that connection to the AS/400. This process eliminates the need to run TCP/IP on the AS/400.

SNA Server 3.0 includes applets for 5250 emulation (as you see in Screen 1) and Open Database Connectivity (ODBC) that Microsoft licensed from StarQuest and an applet for 3270 emulation that Microsoft licensed from NetSoft. In addition, SNA Server includes an applet for an Advanced Program-to-Program Communications File Transfer Protocol (AFTP) client. Microsoft has licensed these applets for use by only one user at a time.

SNA Server 3.0 has also undergone a facelift, and Screen 1 shows SNA Server 3.0's new interface. A new SNA Manager replaces SNA Server's Administration function and provides a graphical interface similar to the Win95 and NT 4.0 Explorer. Besides getting a new look, version 3.0 maintains several features (such as hot backup, load balancing, and multiple network protocol support) from previous versions of SNA Server.

Hot Backup, Load Balancing, and Multiple Protocol Support
SNA Server 3.0 includes several important features from prior releases. The most important of these features is hot backup, which lets you set up a second SNA gateway that activates if the first gateway fails. This feature is important for large networks that need maximum uptime. Figure 1 illustrates how hot backup works.

A hot backup environment requires at least two SNA Server systems &emdash;a primary SNA server and a backup SNA server. The primary SNA server is typically the first one you install. The primary SNA server maintains the configuration files that define the SNA servers and connections, and the backup SNA server maintains a read-only copy of the configuration files. SNA Server uses the primary SNA server when you first establish a connection between the client and AS/400. If the connection between the client and the primary SNA server is broken, the active session to the AS/400 is lost. However, the client system can immediately reestablish a connection to the AS/400 through the backup SNA server. When the primary SNA server system comes back online, any new sessions initiated by the clients will connect through the primary SNA server.

Two other features closely related to hot backup are dynamic load balancing and logical unit (LU) pooling. When multiple SNA servers are available, dynamic load balancing splits the SNA sessions among the different SNA servers. As new clients connect, SNA Server routes them through the SNA server with the lightest load to optimize performance. This feature helps you ensure that the LAN connection to the host functions optimally, without requiring any user or operator intervention.

On the host side, SNA Server supports LU 0, LU 1, LU 2, LU 3, and LU 6.2 protocols. SNA Server also supports host connectivity for physical unit (PU) 2.0, PU 2.1, APPN low-entry networking (LEN) node, and downstream PU (DSPU) devices. An AS/400 or IBM mainframe sees SNA Server on the network as an APPN LEN node. The physical link types that SNA Server 3.0 supports are 802.2 (LAN), Synchronous Data Link Control (SDLC), X.25, channel, DFT (coaxial), and twinaxial.

Another carry-over feature that SNA Server 3.0 provides is support for several network protocols, including native TCP/IP, IPX/SPX, NetBEUI, Banyan Vines, and NT Remote Access Service (RAS). This range of support lets you install SNA Server in various network environments. In addition to the new features and improvements with SNA Server 3.0, Microsoft has made the setup and configuration process easier.

Setup and Configuration
To install SNA Server 3.0, you run setup.exe from the SNA Server CD-ROM. During the installation, you can specify the SNA Server subdomain and the AS/400 link services you want. SNA Server subdomain facilitates fine-tuning hot backup and dynamic load balancing in a large single-domain environment, and the link services define the physical connection to the AS/400.

After the setup process, you can begin to configure SNA Server by running the new SNA Manager. The SNA Server configuration is a two-part process. First, you must manually configure a link service that describes the physical communications link to the AS/400 (this step is in addition to identifying the link services you want). For instance, you can describe a link service as an 802.2 LAN connection, a twinaxial connection, an SDLC connection, and the like. Second, after you configure the link service, you can use one of SNA Server 3.0's new connection wizards to configure new 3270 connections or a new AS/400 connection. To set up SNA Server to connect with an AS/400, select the new AS/400 Configuration Wizard you see in Screen 2 from the SNA Server Manager Tools menu.

This Configuration Wizard guides you through the SNA Server configuration process and helps you specify the AS/400 connection properties and local and remote LU configurations. The remote LU name, which refers to the AS/400, defaults to the AS/400 connection name on the third AS/400 Configuration Wizard screen. The local LU name, which refers to SNA Server, defaults to the value of Local. After you complete the wizard, SNA Server generates the SNA Server configuration file and prompts you to save the new configuration values and use them to restart SNA Server.

The new configuration wizards are a big improvement over configuring previous versions of SNA Server. Although SNA Server has always been easy to configure, the new wizards make configuring the SNA gateway simple. Configuring SNA Server 3.0 is only slightly more difficult than configuring a standard PC-to-AS/400 connection such as Client Access.

SNA Server 3.0's new features and improvements on existing features make it the technical leader in the hotly contested SNA gateway market. SNA Server 3.0 embodies several major technical enhancements for SNA Server, and the new wizards make the gateway configuration easier than ever.

SNA Server 3.0
Contact:Microsoft * 206-882-8080
Web: http://www.microsoft.com/sna
Price: $1359 for a five-user version