SNA Server 3.0 for Interoperability with the AS/400

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

Last November, Microsoft released the latest version of its Systems NetworkArchitecture (SNA) gateway, SNA Server 3.0, which connects networked PCs withIBM 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 increasedclient capacity. The previous limit of 2000 users and 10,000 sessions hasincreased to 5000 users and 15,000 sessions. This new limit makes SNA Server thehighest-capacity SNA gateway available.

Among SNA Server 3.0's new functions, you'll find SNA Print Services, whichprovide server-based 5250 and 3270 printer emulation. SNA Print Services lethost applications print on printers connected to the Windows NT server orattached NetWare servers.

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

SNA Server 3.0 adds several AS/400-specific functions that extend the roleof the SNA gateway. For example, a single logon synchronizes passwords betweenSNA Server and the AS/400 host, thereby eliminating the need to log on multipletimes to access the LAN and the AS/400. With this feature, users can changetheir password on the NT server or the AS/400, and SNA Server changes thepassword on the other system. (You need an ExecuSoft AS/400 add-on to sendpassword changes made on the AS/400 to SNA Server--no matter what OS/400 releaseyou 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/400feature that lets you access AS/400 disk storage from a PC client). SNA Server3.0 supports shared folders via the server. With this new feature, AS/400 sharedfolders appear as one or more drives on the NT server running SNA Server. Allnetworked clients that can access the NT server running SNA Server can accessAS/400 shared folders. The SFG is available for DOS, OS/2, Windows forWorkgroups 3.11, Windows 3.1, Windows 95, and NT clients.

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

With version 3.0, SNA Server can provide AS/400 access via TN5250 withoutrequiring AS/400 TCP/IP. A client system can connect to SNA Server via TN5250and TCP/IP, and then SNA Server can use SNA to route that connection to theAS/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 andan applet for 3270 emulation that Microsoft licensed from NetSoft. In addition,SNA Server includes an applet for an Advanced Program-to-Program CommunicationsFile Transfer Protocol (AFTP) client. Microsoft has licensed these applets foruse by only one user at a time.

SNA Server 3.0 has also undergone a facelift, and Screen 1 shows SNA Server3.0's new interface. A new SNA Manager replaces SNA Server's Administrationfunction and provides a graphical interface similar to the Win95 and NT 4.0Explorer. Besides getting a new look, version 3.0 maintains several features(such as hot backup, load balancing, and multiple network protocol support) fromprevious versions of SNA Server.

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

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

Two other features closely related to hot backup are dynamic load balancingand logical unit (LU) pooling. When multiple SNA servers are available, dynamicload balancing splits the SNA sessions among the different SNA servers. As newclients connect, SNA Server routes them through the SNA server with the lightestload to optimize performance. This feature helps you ensure that the LANconnection to the host functions optimally, without requiring any user oroperator intervention.

On the host side, SNA Server supports LU 0, LU 1, LU 2, LU 3, and LU 6.2protocols. 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 APPNLEN 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), andtwinaxial.

Another carry-over feature that SNA Server 3.0 provides is support forseveral network protocols, including native TCP/IP, IPX/SPX, NetBEUI, BanyanVines, and NT Remote Access Service (RAS). This range of support lets youinstall SNA Server in various network environments. In addition to the newfeatures and improvements with SNA Server 3.0, Microsoft has made the setup andconfiguration 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/400link services you want. SNA Server subdomain facilitates fine-tuning hot backupand dynamic load balancing in a large single-domain environment, and the linkservices define the physical connection to the AS/400.

After the setup process, you can begin to configure SNA Server by runningthe new SNA Manager. The SNA Server configuration is a two-part process. First,you must manually configure a link service that describes the physicalcommunications link to the AS/400 (this step is in addition to identifying thelink services you want). For instance, you can describe a link service as an802.2 LAN connection, a twinaxial connection, an SDLC connection, and the like.Second, after you configure the link service, you can use one of SNA Server3.0's new connection wizards to configure new 3270 connections or a new AS/400connection. To set up SNA Server to connect with an AS/400, select the newAS/400 Configuration Wizard you see in Screen 2 from the SNA Server ManagerTools menu.

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

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

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