What is SNA Server?

Microsoft SNA Server is an SNA gateway that connects LAN-based PCs with IBM host systems running SNA (Systems Network Architecture) protocols. SNA Server accomplishes this with excellent ease of use, economy, performance, reliability, security, and flexibility, as well as with broad ISV/IHV industry support. SNA Server delivers these broad benefits through an equally broad set of features that include

Complete compatibility with existing Novell® Network protocols, cards, and drivers. Familiar and easy-to-use GUI for installation, administration, and troubleshooting.

Complete SNA coverage (APIs, LU and PU protocols, datalink protocols).

The highest capacity of any SNA gateway (for sessions and clients and for servers per domain).

Centralized and remote administration, including administration via IBM NetView® and RAS (Remote Access Service).

Support for centralized and branch configurations.

The greatest security of any SNA gateway (SNA Server is designed to meet C2-level security).

Load balancing, hot backup, and other fault-tolerant features.

Support for every key corporate desktop system and LAN protocol (including IPX/SPX and TCP/IP).

Open, modular, extensible architecture.

A design that is scalable, multiplatform, and compatible with symmetric multiprocessing (SMP).

Complete context-sensitive help and online documentation.

Complete functionality provided in one package.

SNA Server is a server process that runs on the Microsoft Windows NT™ Server operating system. SNA Server utilizes both the native Microsoft Windows NT™ communications protocol (such as TCP/IP or IPX) and IBM SNA protocols, acting as a high-speed gateway between the PC and IBM networks. SNA Server's bidirectional communication provides terminal emulation, printer emulation, file transfer, and program-to-program communications. SNA Server supports client functions on all the popular PC operating systems

including Windows NT, Microsoft Windows®, MS-DOS®, OS/2®, UNIX®, and Macintosh®.

By supporting software such as 3270 or 5250 emulators, SNA Server makes data and applications residing on IBM hosts available to PCs for use with desktop productivity software such as Microsoft Excel.

SNA Connectivity, PCs, and LANs

IBM SNA connectivity has gone through four phases. Initially, terminals were connected through terminal controllers (for example, 3274s) to mainframes. In the second phase, terminals were replaced by PCs, each of which had a coax card (for example, an IRMA card) to connect to the controller. In the third phase, PCs began being connected to each other on LANs. In most cases, the LANs were just used for file sharing—the PCs still kept their coax-card connections to the mainframe. In the fourth phase, PC gateways made it possible to use LANs for host connectivity and to more easily link the IBM and PC worlds. With the fourth phase comes a change in the role of mainframes from stand-alone systems to application servers and data repositories integrated with the enterprise internetwork and LAN-connected PCs.

As the value of LAN-connected PCs and client-server architecture has grown, it has come to play an important role in running organizations, a role so important that integrating PCs with host computers is critical to the effective operation of enterprises with legacy systems.

Benefits of SNA Server

1 ) Benefits to the Desktop User

SNA Server reduces complexity, increases stability, and saves memory by allowing you to use only one protocol. In contrast, when connecting directly, you will need the DLC protocol to

connect to the host, plus your favorite LAN protocol, such as TCP/IP or IPX/SPX, to connect to the file/database/mail server.

In many cases, the DLC protocol simply will not work or coexist with certain types of adapters and/or other protocols. The DLC protocol is a terminate-and-stay-resident (TSR) program and thus requires a real mode NDIS or ODI driver. In addition, IBM's DLC protocol (LAN Support program) only works with certain adapters and protocol stacks. Connecting PCs through SNA Server allows you to get rid of these TSRs and MS-DOS device drivers.

2) Benefits to the LAN Administrator

SNA Server provides easier administration. When connecting direct, each desktop must be configured individually with the host's network address, LU name, and so on. Whenever there's a change on the host side, such as the host's network address, all desktops must be reconfigured. With SNA Server, there's nothing to configure at the client; all host changes can be tracked centrally by the LAN administrator.

SNA Server provides integrated security for all users. The LAN administrator can control access to the host by using the combined security features of Windows NT Server and SNA Server. In contrast, direct connection allows each desktop user to access the host by simply knowing the applicable host parameters. A gateway adds another level of flexible security.

Performance and troubleshooting tools are available. When all host-bound traffic is concentrated through SNA Server, the LAN administrator can use the performance monitoring, event logging, and tracing/sniffing capabilities of the server platform. An individual desktop problem is easier to work around by simply assigning a new LU, and tracing and debugging can be done at the server without interrupting the work of desktop users.

3) Benefits to the Host Administrator

SNA Server dramatically reduces (re)definition work on the host. You can support hundreds of users by defining a single PU or controller, instead of having to define one for each user. Especially on mainframe systems,. Less definition work also means fewer definition errors, each of which can be costly.

SNA Server also reduces host memory requirements. All these hundreds of definitions are typically stored in resident memory on the host system, consuming excessive amounts. Memory savings can result in hardware savings and in improved host performance..

SNA Server reserves host CPU cycles for what the hosts are intended for—running applications. If you have direct connections to the host, each of these connections must be managed individually by the host's control software, consuming many CPU cycles. SNA Server saves network bandwidth. Instead of the host having to poll all desktops individually to maintain direct connections (even when there's no activity), the host has to maintain only one connection when using a gateway. This can dramatically reduce network noise and allow better network performance as well as reduce session time-out problems.

. How Can SNA Server Be Used?

SNA Server is being used in several different ways to connect PCs and host computers:

It provides large-scale and fault-tolerant connectivity for users on LAN-connected PCs to run interactive host applications. Using powerful automation tools of today's terminal emulators, this access can be re-engineered, presenting the user with a forgiving and intuitive graphical interface.

It can provide connectivity for TN3720 users without complicating the mainframe configuration with the requirement to support TCP/IP.

It can act as a database gateway, allowing secure access to SNA host databases via ODBC, directly from workstations on the LAN.In an enterprise whose wide-area backbone is still based on SNA protocols, SNA Server can be used to integrate LANs across branch offices as well as with corporate data and applications (both uses are shown below). SNA Server also provides the means to administer such a network.

Using RAS over SNA, a workstation in a remote office on an SNA backbone can access any resource across the SNA link, as long as necessary permissions are granted for the resources. Using RAS over SNA is most suitable for remote administration because of the typically slow SNA links. In these ways, each remote site in the enterprise can transparently share files, printing, electronic mail, and databases.

SNA Server 2.1: Features

Graphical User Interface

SNA Server's tools are designed to make SNA Server extremely easy to install, configure, manage, and use. These benefits may significantly reduce training and support costs. SNA Server uses the latest in graphical user interface design and usability testing to make the administrator's task as easy as possible.

Admin

The Admin display contains three windows (Servers and Connections, LU Pools, and Users and Groups) that are similar to the File Manager in structure and functionality, making the administration of SNA Server intuitive. Drag and drop allows you to quickly set up LU pools and assign users to them. Icon-based visual feedback allows an administrator to readily identify servers, connections, LU pools, and users, as well as the type of connection . whenever the status of any object changes, the administrator can view the change immediately.

Dialog Boxes

Easy-to-understand dialog boxes help you map parameters from the VTAM Gen or AS/400 configuration to settings within SNA Server. Regardless of whether the administrator has a LAN background or has experience working with the host, SNA Server is designed to make it easy to manage the PC-to-host connectivity. Automatic configuring of several host parameters also saves time and reduces configuration errors.

SNA Trace

A simple dialog box allows you to record messages to and from SNA Server, as well as activity into and out of SNA APIs and activity within the software components of SNA Server.

SNA Trace Options --- Windows NT Tools

These include User Manager, Performance Monitor, Event Viewer, and Control Panel applets. Integration with Windows NT is tight, so that the tools appear as seamless extensions of SNA Server.

Centralized Monitoring and Control

SNA Server's tight integration with the Windows NT Server allows administrators to manage all of the SNA servers from a single location. This allows MIS organizations to utilize SNA servers as part of their distributed client-server systems while maintaining centralized security and control.

SNA Server provides centralized comprehensive monitoring and administration of routine operations and problem diagnosis through the SNA Server Admin program and tools, Windows NT graphical tools, and host-based NetView. The Admin program runs on any Windows NT platform and provides the tools the LAN administrator needs to manage day-to-day SNA/LAN interaction. NetView capability provides communications between SNA servers and host operators. Windows NT graphical tools are tightly integrated with SNA Server and provide a broad range of capabilities for controlling, diagnosing difficulties, and monitoring.

•Link Services Management. Link services can easily be installed, configured, or removed with SNA Server Setup, which also displays the mapping between Windows NT device driver names and SNA connections. Individual drivers can also be started and stopped in the Windows NT Control Panel through the Devices applet.•Connection Management. Admin displays the status of SNA servers and connections (inactive, pending, active, stopping); allows you to create, delete, start, and stop them with the click of a button; and provides activation flexibility for connections. A connection can be activated manually, at server startup, or on demand when a client accesses it..•LU Management. Admin allows you to quickly create a range of LUs for a connection, and group them into pools to provide user access. When you highlight a connection, Admin displays the associated LU information: the name, status, and user activity for each LU. •User Management. Admin displays users and groups as well as the sessions for users who have been granted SNA access. Admin also allows you to assign LUs or LU pools to users and view or modify a user's properties.•Configuration Management. Admin allows you to open, save, back up, and restore multiple configuration files. In a multiserver environment, the primary server holds the master copy of the configuration file; this copy is replicated to backup servers, if they are available. If the primary server goes down, backup servers provide the configuration information to clients and other servers.•Batch-mode Configuration. In addition to the graphical tools provided by Setup and Admin, SNA Server provides a command-line utility, snacfg. You can use the command-line interface to easily modify an off-line configuration file without starting the graphical interface, or to store configuration commands in a command file, so that they can be carried out easily.•Troubleshooting. For extensive troubleshooting capability, SNA Server provides the SNA Trace tool, support for Response Time Monitor (a feature of some 3270 emulators), NetView utilities (NVAlert, NVRunCmd), and integration with Windows NT tools (Event Viewer, Performance Monitor).

•Performance Monitoring. SNA Server's integration with Windows NT Performance Monitor allows you to graphically monitor SNA objects (link services, PUs, LUs), to tune performance or help diagnose difficulties in real time.•Remote Administration. For flexible administration of distributed SNA servers, SNA Server Admin can be used across routers and bridges, and remotely over a RAS

Enterprise Configuration Flexibility

SNA Server has the advantage of being able to be set up in a centralized configuration or a distributed configuration, depending on customer needs. It functions equally well in either configuration.

Branch Configuration

SNA servers can be located in branch offices on server systems that are also used for printing, databases, electronic mail, and fax. This configuration reduces traffic on the WAN and increases responsiveness to user needs through local management of connections, LUs, and security. A distributed configuration would be a good choice for low-bandwidth WAN links (for example, X.25 or low-speed leased line backbones) using multiprotocol routers, or when only an SNA backbone is in place.

Centralized Configuration

Alternatively, SNA servers can be located at the data center to maximize reliability and security. This configuration makes it easy to arrange load balancing and hot backup, makes it easier for MIS personnel to manage the servers, and reduces the need for SNA expertise at remote sites. Centralized configurations are good when you have high-bandwidth WAN links (for example, high-speed leased line or frame-relay backbones). Centralization allows you to use a single, routable protocol (for example, TCP/IP or IPX) on all WAN links in the enterprise. You can route TCP/IP or IPX from clients over the WAN to SNA servers at the central site; in turn, the SNA

servers can be connected to the FEP or AS/400 via token ring, or directly attached to the mainframe channel.

Network Security

Many MIS managers are used to having security programs on the mainframe (such as RACF and Top Secret) to guard access to the host. Traditionally they have been reluctant to move applications to LANs because of the lack of robust security.

Guards Corporate Data SNA Server guards against unauthorized access to corporate data by providing security designed to meet the US government C2 level, via controlled logon to a Windows NT Server domain. The logon must succeed before access is given to any services provided by SNA Server.

Provides Flexible Control In addition, SNA Server provides the flexibility to allow an administrator to control access from the LAN, the host, or both. In addition, remote access over RAS is equally secure because it employs the same user account database. By using the user accounts database in a Windows NT Server domain, SNA Server allows you to create user and group accounts only once for use by both Windows NT and SNA Server. A simple dialog box in SNA Server Admin allows you to specify which users and groups defined in the domain will be granted access to SNA sessions.

Administrative Permissions The administrative permissions that you can set in SNA Server Admin are read-only, read/write, full control, and no access. These permissions control access to SNA Server tools as well as access to the configuration file.

Full Audit Tracking Full audit tracking is provided through integration with the Windows event log. (The ability to track all activity that occurs on a server is a requirement for designs that meet C2-level security.) The auditing capabilities compare to auditing capabilities common on hosts, helping make MIS managers comfortable with moving to SNA Server and Windows NT Server.

Convenient Single Logon A product designed to meet C2-level security need not be inconvenient. SNA Server provides a single network logon for greater user productivity. Users only need to log on to an SNA server once to access all SNA servers. This also allows the network administrator to manage each user account centrally. Access to network servers, printers, applications and other services are defined for each user by the administrator from this single control point. Once logged on, users have seamless access to all the network resources that have been assigned to them. This single logon process makes it faster and easier for users to get the information they need when they need it.

SNA Gateway Reliability

High reliability is another benefit that comes from the tight integration of Windows NT Server and SNA Server. Within a Windows NT Server domain, SNA servers are able to recognize each other transparently and are able to dynamically back each other up or route traffic to the least-loaded server to increase throughput. These SNA Server features are known as hot backup (dynamic session fault-tolerance) and load balancing. With them, SNA Server provides high reliability to mission-critical data and applications. These two benefits are also a consequence of SNA Server's advanced LU pooling feature, which allows administrators to group multiple LUs on a single server or across several servers.

Hot Backup Hot backup helps ensure minimal downtime for host access by rerouting sessions over alternate paths when a communications failure occurs. SNA Server implements hot backup through multiple connections within a single server, or through multiple servers within a domain. SNA Server's unique LU pooling feature facilitates hot backup. An administrator groups LUs (from one or more servers) into a pool. If a data link on a server fails, SNA Server can dynamically reroute lost sessions through other pooled LUs (using other data links). Similarly, if an entire server in a multiserver domain fails, SNA Server can dynamically reroute sessions to pooled LUs on other servers.

Load Balancing Automatic load balancing across multiple servers automatically routes new LU sessions to the least-busy SNA server to deliver maximum availability of corporate data and minimum response time. SNA Server's ability to dynamically route traffic across multiple servers minimizes response time between the desktop and the host, making users more productive.

Fault-Tolerant System Recovery Capabilities SNA Server's tight integration with Windows NT Server provides numerous facilities that protect both data and the system from errant applications or external issues such as hardware or power failure. There are recovery procedures that protect data even if it is unsaved. Windows NT Server provides several tools that enhance system reliability and aid in recovering from problems including: UPS, tape backup, registration database, disk duplexing, disk mirroring, and disk striping with parity.

An Open Platform for SNA Connectivity

SNA Server supports all the popular desktop machines, is LAN protocol-independent, has a device interface that allows you to choose from a wide variety of link types and adapters, and has open 3270/5250 emulator interfaces for ISVs.

Supports Key Corporate Desktops

SNA Server allows customers to maximize returns on their desktop investments by supporting client or downstream systems running MS-DOS, Windows 3.x, Microsoft Windows for Workgroups 3.1 and 3.11, Windows NT, OS/2, Macintosh, and UNIX operating systems.

Protocol Independence

SNA Server can meet a broad range of enterprise computing requirements, and is especially suited to providing host access over heterogeneous networking environments. SNA Server provides native support for most popular client-server protocols including named pipes, TCP/IP, IPX/SPX , Banyan VINES IP, AppleTalk, and RAS.

Open SNA Device Interface

SNA Server allows for a wide variety of data links from the server to the host. The SNA Device Interface Specification (SNADIS) allows third parties to easily create SNA Server drivers for their adapters. Data links currently supported by SNA Server include 802.2/LLC (Ethernet, token ring, and FDDI), SDLC, X.25/QLLC, DFT, Twinax, and Channel attachment.

Open 3270/5250 Emulator Interfaces

The specifications for creating both desktop emulators and back-end link services are broadly available. This ensures that as new technologies become popular, they will very quickly become available to SNA Server customers.

Modular, Extensible Architecture

In SNA Server, the DMOD module provides network-independent communication between the various components in the SNA Server system. Components use the same interfaces for both local and remote access. Through the DMOD, SNA Server provides an extensible interface that can easily grow to support more client-server transports.

A significant benefit of SNA Server is its ability to support client-server communications over a wide variety of communications transport protocols. Each transport provider presents a consistent message exchange interface to the DMOD. Each handles session establishment, user authentication, and multicast message support in the unique manner of its transport. Equally important, transport providers are responsible for "advertising" SNA Server in a native fashion on each of their respective networks. Examples of the ways this is done are mailslots on Microsoft LAN Manager (local area network software) networks, Service Advertising Protocol (SAP) and Bindery queries on NetWare, and Name Binding Protocol (NBP) on AppleTalk networks.

Full Support for WOSA SNA APIs

All SNA Server APIs are fully compatible with the WOSA (Windows Open Service Architecture) SNA API standard. Each SNA vendor provides client software in the form of a DLL driver to

translate WOSA SNA API calls into the native function calls of the respective services. This allows a Windows-based application to communicate with another vendor's SNA product.

•WOSA provides a consistent interface to enterprise computing environments, thus hiding the complexities of connectivity from applications and application developers.•All the SNA Server's APIs are fully compatible with WOSA's SNA API standard.•WOSA is endorsed by 20 leading SNA vendors, including: Andrew Corporation, Attachmate, Data Connection Ltd., DCA, Easel, Eicon Technology, FutureSoft, IBM, ICOT, ICL, Microsoft, MultiSoft, NCR®, Novell, NetSoft, Olivetti®, Siemens-Nixdorf, Systems Strategies, and Wall Data™.•WOSA provides the same API for 16-bit and 32-bit for more efficient multienvironment development.•WOSA is the SNA API standard for Windows.•WOSA is IBM OS/2-compatible. In addition to the OS/2-compatible APIs, Windows API extensions are available for asynchronous communications.

Downstream PU (DSPU) Support

Downstream connections and LUs allow an SNA Server to support clients (such as IBM Communications Manager/2 systems) that do not use the SNA Server client-server interface. Multiple DSPUs can connect simultaneously to a single SNA server. This function is also known as PU concentration.

To the downstream system, there appears to be a direct connection to the host. SNA server accomplishes this by passing detailed LU information back and forth between downstream systems and host. SNA Server does require all the usual connection information for the host and downstream connections. Communication via a downstream connection and downstream LU in SNA Server is always controlled by the host.

Although use of the DSPU connection for clients does not provide all the benefits of the regular SNA Server client-server connection, there are still significant benefits to employing SNA Server for DSPU clients:

•A full range of client-server transports is supported for DSPU clients: 802.2/LLC over token ring or Ethernet, SDLC, and X.25/QLLC.•SNA Server performs PU concentration rather than PU pass-through. This reduces the network configuration and administration workload as well as the memory consumption at the host.

•DSPU clients can share the SNA Server host connections.•DSPU clients can be supported along with regular clients, allowing for easy coexistence of various types of clients.

See full-sized image.

Downstream Physical Unit Connection

SNA Server as a PU Concentrator

SNA Server's ability to act as a PU concentrator allows multiple downstream physical units (DSPUs) to be merged into a single upstream connection to the mainframe. SNA Server acts as mini-SSCP, maintaining a full PU 2.0 protocol stack, which it uses to pass information from downstream LUs along upstream connections to the mainframe. As a PU concentrator, SNA Server leverages both mainframe and PC resources. On the mainframe side, operations can be simplified because there are fewer distinct PUs to configure and manage, and more clients (users) can be connected to the mainframe without having to upgrade. For example, three PUs, each using two LUs, could instead appear to the mainframe as only one PU with six LUs on it. Other benefits of PU concentration include providing a convenient demarcation point between responsibilities of local personnel and IS personnel; allowing an SNA Server to accommodate a wide variety of SNA devices and software; and performing link-level conversion (for example, from 802.2 protocol downstream to SDLC upstream). PU concentration is appropriate only to dependent LUs.

DSPU mapping LUs to upstream connection

Complete SNA Protocol Coverage

SNA Server provides support for all SNA APIs, LU protocols, PU protocols, and data link protocols. SNA Server's SNA API support provides very flexible development options. SNA Server APIs, supported by 20 leading SNA vendors, have gained broad industry support from established emulator, adapter, and gateway vendors. The SNA APIs support both synchronous and asynchronous calls. Handling the client-server I/O using asynchronous calls improves performance by improving pipelining of I/O operations. Asynchronous calls also return control to the application immediately so that it can perform other tasks while the requested I/O operation proceeds independently. This is particularly important in the non-preemptive environment of Windows 3.x.

The APIs included with SNA Server are as follows:

•APPC: For developing 5250 emulators, as well as applications that communicate peer-to-peer with other APPC applications using the LU 6.2 protocol. Management verbs are also supported.•CPI-C: For developing applications that communicate peer-to-peer with other applications using the LU 6.2 protocol.•CSV: For developing applications that include tracing of API calls, communication with NetView, and EBCDIC to ASCII conversion.•LUA: For developing applications (using LUA/RUI or LUA/SLI APIs) that need direct access to the LU 0, 1, 2, 3 data streams. Supports ISV 3270 emulators via the open 3270 EIS API.•EHLLAPI: For developing applications that interface with existing 3270 or 5250 applications. Note that EHLLAPI is offered by ISVs, but not by Microsoft. (EHLLAPI is not included in the

3270 and 5250 applets in SNA Server.)

Complete SNA PU and LU Protocol Support

SNA Server provides transparent PC-to-host connectivity in a wide range of customer environments. In addition, SNA Server allows you to mix any LU, PU, and data-link protocols concurrently in the same server.

LU Protocols SNA Server supports LU 0, LU 1, LU 2, LU 3, and LU 6.2.

PU Protocols SNA Server supports PU 2.0, PU 2.1, APPN LEN Node, and DSPU (downstream PU). Note that Low-Entry Networking (LEN) support is what allows SNA Server to participate in an APPN network. (SNA Server does not have to support APPN Network Node or APPN End Node to be able to gain full connectivity into an APPN network.)

Data Link Protocols SNA Server supports 802.2/LLC, SDLC, X.25/QLLC, DFT, Twinax, and Channel attachment. For a complete list of compatible third-party data-link products from ISVs/IHVs, see the Companion Product Catalog.

Comprehensive Client-Server Support

Client-Server Protocols SNA Server provides native support for a wide range of client-server protocols: IPX/SPX, TCP/IP, RAS, Named Pipes, AppleTalk, and Banyan Vines IP.

Clients Supported Windows 3.x, Windows for Workgroups, Windows NT, MS-DOS, Macintosh, UNIX, and OS/2 1.x and 2.x are clients that are all supported by SNA Server. In addition, SNA Server's flexible client support allows you to mix NetWare clients, Microsoft clients, TCP/IP clients, Banyan clients, Macintosh clients, TN3270 clients, and DSPU clients in any way on the same server.

Highest Capacity of any SNA Gateway

SNA Server provides the highest capacity of any SNA gateway on a PC platform at every level (LUs, PUs, clients, and sessions). It also allows servers to be added to meet the high demands of large enterprises linking thousands of PCs. SNA Server supports:

•Up to 250 simultaneous connections (PUs) per server, in any combination of upstream (host), peer-to-peer, and downstream (DSPU) connections.

•Up to 2,000 clients per server.

•Up to 10,000 LU sessions per server.

•Up to 50 SNA servers working together in a Windows NT Server domain for load balancing and hot

backup.

NetView Integration

A variety of diagnostic tools can be used with SNA Server that allow you to collect information about the sequence of events leading up to a difficulty and the exact state of the system when the difficulty occurred.

Response Time Monitor

Response Time Monitor (RTM) is an IBM NetView function that measures the length of time it takes a host to respond during a 3270 session. The SNA Server Admin tool lets you specify the times at which RTM should send data, and also lets you define the triggers that will cause RTM to register that the host has responded. Note that in order for your 3270 users to use RTM, their emulators must support it.

NetView Support

NetView is a network management system that runs on an IBM host. It receives alerts and helps a NetView administrator manage operations, diagnose problems, and improve system performance. Additional NetView services provided by SNA Server include NVAlert and NVRunCmd.

NVAlert. Allows alerts generated by the Windows NT system or by Windows NT-based applications to be forwarded to a host system. This means that not only SNA Server events, but also system events such as a disk becoming full, or an application failing to find a file, can cause an alert to be sent to the host. Examples of information that can be forwarded to a host include data on connection failures, session statistics from 3270 emulators, and information from LUA applications

NVAlert Service

NVRunCMD. Allows Windows NT commands that are typed at a host-system NetView console to be carried out on any Windows NT Server running SNA Server, with results being sent back to

the host. The NVRunCmd service runs as a background process on the SNA server, waiting for a command to be sent from a NetView console. If, as in the preceding example, the NetView operator receives an alert that an application did not find a file, the NetView operator could execute a command on the Windows NT Server system to copy the file from one directory to another (so the application would find it).

Optimized Server Design

SNA Server offers 32-bit implementation, multithreaded architecture, and tuned scalability on SMP systems, extensive use of asynchronous I/O, maximum SNA RU sizes and LAN protocol packet sizes, and dynamic management.

•Preemptive multitasking. Provides the responsiveness required to support multiple applications and multiple users on a single server.•Multithreading. Facilitates the design and development of responsive applications.•Symmetric multiprocessing (SMP). Provides scalable processing power, effectively without limits, meeting the needs of large enterprises while providing small organizations with room to grow. SMP scalability also delivers superior price/performance, since performance can be increased without adding new servers.•Portability. Offers portability across Intel, MIPS R4x00, and Alpha AXP RISC-based systems, to provide a choice of hardware architectures. SNA Server supports the platforms Windows NT supports, which will soon include the PowerPC platform.•Advanced fault tolerance. Provides the data integrity required for important business applications.•Virtual memory. Ensures that the system will always run without running out of memory under peak

loads. This also allows SNA Server to run with less memory than would otherwise be required.•Distributed interprocess communications. Enables client-server applications to be written easily and independently of the underlying network.•Security designed to meet the C2 level. Provides full discretionary access so that business data can be accessed by the right people in the right way.•Support for multiple network interface cards on one segment. Provides extra network bandwidth that can be added to support additional users.•Multiple applications. Allows a Windows NT Server running SNA Server to simultaneously support other Windows applications such as database software. SNA Server does not have to run on a dedicated machine.

Integration with Windows NT

SNA Server is tightly integrated with Windows NT Server in ways that provide an easy, flexible, efficient, reliable, scalable, and secure platform for MIS and LAN administrators to manage the host/PC interconnection. Windows NT Server provides the administrator with consistent and easy-to-use graphical tools to perform all administrative tasks on SNA Server and the Windows NT Server. The primary tools offered are the Control Panel applets, User Manager, Performance Monitor, and Event Viewer.

Control Panel The Control Panel on the Windows NT Program Manager contains many useful tools for controlling different components of SNA Server.

Services applet The Services applet controls Windows NT Networking services individually. Services can be started, stopped, paused, and continued. For example, you can stop the NVRunCmd service if you don't want a NetView operator to run commands on the SNA server.

Network applet The Network applet is the tool you use to install and configure your network cards, and to install and configure network protocol stacks. This is also the tool you would use to join a workgroup or a domain. The networking architecture within Windows NT Server lets you support multiple simultaneous network cards and multiple simultaneous protocols in a single machine. You can have one card and multiple protocol stacks, or one protocol stack and multiple cards.

Devices applet With the Devices applet, you can stop, start, and set the startup value for system drivers, adapter drivers, and network protocols. This applet also reports the status of devices.

Server applet The Server applet allows you to monitor who is connected to your machine and what shared resources are in use. This tool is also used for setup, directory replication, and administrative alerts.

Event Viewer This utility allows you to record and view significant events generated by the Windows NT Server system or Windows NT-based applications such as SNA Server. Event Viewer can notify administrators of critical events with pop-up messages, or add event information to log files. The information allows you to better understand the sequence and type of events that led up to a particular state or situation.

Performance Monitor Performance Monitor is a graphical tool which can be used to measure the performance of any SNA server accessible over the network. It allows you to monitor several aspects of your server's performance in real time in the form of charting, triggers (causing alerts to be sent or programs to be started), tables of values, and logs. Performance Monitor is very useful for system tuning and diagnosis. The parameters that can be monitored for SNA servers include throughput and transmission volume (in bytes, or in some instances, frames), and can be measured for connections, LUs, or adapters.

User Manager All user and group accounts are managed with the User Manager. The accounts established through User Manager are also used by SNA Server, so that you need only create an account once for use by Windows NT Server or SNA Server. A simple dialog box in SNA Server Admin allows you to specify which users and groups defined in the domain will be SNA Server users and groups.

Account Management and Domains Windows NT supports managing accounts by logical groups of servers, called domains. While the primary server holds the user account database, users can log on to other servers in the domain that have a copy of that database. Requiring only a single account in the entire domain is an effective way to manage an enterprise that includes hundreds of servers and thousands of users.

Advanced Features of SNA Server

LU Pooling SNA Server implements a feature called LU pooling to maximize access to the resources available via 3270, LUA, or downstream LUs. A user, LUA application, or downstream system using the pool can get LU access as long as one of the pooled LUs is available. Pooling of LUs is handled differently for APPC LUs but provides the same capabilities. LU pooling can provide a variety of benefits.

Session Efficiency Pools allow groups of intermittent users to use resources efficiently. For example, ten 3270 users who only need intermittent access to more sessions may find that a pool of five 3270 LUs is adequate for their needs.

Hot Backup Hot backup is a benefit of SNA Server's LU pooling capability. LU pooling (and thus hot backup) can be implemented across multiple SNA servers and across multiple adapters within the same SNA server. If one server or adapter stops working, SNA Server can reestablish user sessions in just a few seconds. Users may lose their session temporarily but when they reconnect they will immediately get a new session.

Load Balancing Load balancing is also a benefit of SNA Server's LU pooling capability. An LU pool is set up to contain LUs from more than one SNA server. When a new user who has been

assigned pool resources logs on, SNA Server automatically assigns LU resources based on the number of users accessing each server. This balances the load between servers and makes efficient use of SNA servers (as compared to using up the capacity of one server before assigning resources from another).

Administrative Efficiency Using SNA Server Admin, the administrator can assign LU pools to users or groups. This eliminates the time that would be required to assign LUs individually. And with SNA Server's drag and drop capability, constructing pools and assigning users to them can be done with a few mouse clicks.

RAS (Remote Access Service) Support

RAS works with SNA Server in two ways.

•First, RAS can provide connectivity to SNA Server using asynchronous, X.25, or ISDN connections. This provides a remote connection to an SNA network or LAN by the use of a modem, X.25 card, or ISDN adapter as a network card.•Second, RAS can run over SNA using LU 6.2 as a transport. This provides a way to connect to and manage an SNA server using the SNA network as the physical connection.

Remote Access Service (RAS) for the Windows NT Server enables users to participate fully as a network client from remote locations. RAS can be set up on any machine that can run Windows NT. With RAS, a number of functions can be performed transparently on remote workstations, including:

•Network management•File and print sharing•Electronic mail•SQL database access•Emulation

Because RAS is supported as just another transport, all SNA Server functions, emulation, application-to-application communications, and administration can be performed over an asynchronous connection.