http://www.microsoft.com/TechNet/boes/bo/sna/ypages/bus-tech.htm (PC Press Internet CD, 03/1996)
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Overview
SNA Server and the Benefits of Using SNA Gateways
SNA Server Integrates Heterogeneous Environments
IBM 3172 and Bus-Tech Technology
Summary
Many large organizations have come to the realization that, despite some impressive efforts to the contrary, departments and even entire divisions have adopted computing infrastructures that are based on a variety of non-SNA protocols. If the organization has a mainframe or AS/400® computing foundation, integrating these non-SNA networks into SNA eventually becomes an end user requirement. Achieving that integration with high capacity LAN-to-mainframe access while using an industry standard connectivity platform has been a difficult proposition, until now. Through an unprecedented combination of products from Bus-Tech, Microsoft®, and IBM®, it is possible to provide multiple LAN protocol access to mainframe and AS/400 applications through a high capacity, industry standard connectivity platform - the Bus-Tech 3172-NT.
This white paper provides a brief and general description of IBM's System Network Architecture (SNA), describes the components of the 3172-NT and explains how the evolution of mainframe access products and requirements has lead directly to the creation of the Bus-Tech 3172-NT.
In order to understand the unique and powerful benefits of the Bus-Tech 3172-NT, it helps to have an awareness of the traditional method of mainframe access and its underlying structure.
The traditional method for terminal and programmatic access to mainframe applications, and printing of the application data, is achieved through the use of IBM's System Network Architecture (SNA). The term SNA has been used to encompass the entirety of the hardware and software components that comprise an SNA network. For the purposes of this white paper, SNA is broken down into three major areas -
The actual network protocols are defined within SNA as Logical Units, or LUs. Different LUs provide different services and they are divided into five basic categories: LU0, 1, 2, 3, and 6.2. LU0 is a general purpose LU for the development of specialized applications. LU1 and LU3 are defined to carry printer data to system and network printers. LU2 defines how terminal related data will be formatted and transmitted. And, LU6.2 is an inter-program communications LU. LU6.2 is also known as APPC (Advanced Program to Program Communications) and is the network underpinning of a wide variety of Application Programmatic Interfaces, including CPI-C, EHNAPPC, and DRDA. LU6.2 has also evolved into somewhat of a general purpose LU that can provide terminal connectivity as well as file transfer capabilities.
The hardware devices and, abstractly, the administration software that resides on the devices in a traditional SNA network also have definitions that govern what purpose they serve within the network. The physical devices, and their software, that transport the protocols and manage and control the resources that are directly attached to them are defined as Physical Units, or PUs. Physical Units are currently divided into four categories. They are PU Types 2, 2.1, 4, and 5. PUs can be easily understood if you keep in mind their hierarchical nature. They are like direct reports within a military organization. With certain exceptions, each PU talks only to the next in the chain of command. And, they only pass information on the LUs that have been assigned to them and are under their direct control. Each LU in an SNA network is assigned to a PU that manages and controls it.
Figure 1
PU Type 5 is the top of the hierarchy and is expressed in the mainframe by a controlling software component dubbed VTAM™ ( Virtual Telecommunications Access Method ). VTAM typically communicates directly to a PU Type 4 which is expressed in a hardware device that is called a Front End Processor, or FEP. Standard IBM nomenclature for these devices is 3745 or 3746 and they generally employ a management program called ACF/NCP, or Advanced Communication Function/Network Control Program. The NCP within a PU Type 4 controls and manages the resources of the next level closer to the end user, a PU Type 2. PU Type 2 is expressed in devices like an IBM 3174 Cluster Controller. An IBM 3174 is generally the last point of resource control prior to the actual end user or printer. PU Type 2.1 is the exception to the hierarchical model. PU 2.1 is the basis for Advanced Peer-to-Peer Networking (APPN) and is used in AS/400 networking. PU 2.1 and APPN grew out of a need for midrange systems to create their own SNA network environment without the involvement of a mainframe, a PU 5.
There is tremendous historical, and current development, variety of the LU and PU combination theme. This description has been to provide general information about "traditional" SNA and its components.
With all that said, Figure 1 illustrates a simplified configuration of an SNA network. In this example, "dumb" terminals, such as IBM 3270 devices, are single purpose devices that have access to mainframe applications first through a 3174 Cluster Controller, then through a 3745 FEP with ACF/NCP and into VTAM for connection to the applications.
This was the basic host access model for large organizations prior to the introduction of Personal Computers and terminal emulation software. This "traditional" access model was sufficient when there were few accepted alternative computing platforms and few networking choices. However, as organizations started to adopt alternative computing platforms that did not support the proprietary SNA model, users were suddenly forced to have multiple terminal types on one desktop to access the various computing platform applications. Further, as low cost applications on Personal Computers became available to provide solutions for rudimentary tasks, such as departmental word processing or spreadsheet creation, it became apparent that PC's could be a superior desktop computing machine if outfitted with a terminal emulator for access to SNA based applications.
Figure 2
The next phase of evolution is characterized by Personal Computers showing up on desktops containing terminal emulation software and a hardware adapter that allowed for direct connectivity into the 3174 via coaxial cable connections. Figure 2 illustrates this approach. DCA with its IRMA connectivity options probably best represents this era of PC-to-host connectivity. The early drawbacks of this approach were lead by the unseemly fact that you were taking an autonomous computing device, the PC, and turning it into a "dumb" terminal for the duration of your host connectivity. In some cases, the system had to be re-started to access any local applications after log off from the host sessions. This clearly defeated the objective of having an on-demand, multi-application device on everyone's desktop. Fortunately, this phase was to be relatively short-lived.
With the advent of Personal Computer networking, departments now had the ability to share files, applications, and printers among many networked systems. These meteorically popular non-SNA networks gave rise to the first LAN-to-SNA gateways. The gateways allowed connection to a variety of SNA services typically through coaxial cable connections into 3174 Cluster Controllers. They were adequate for small networks with low capacity requirements and generally provided SNA access for a single network type, i.e. TCP/IP, IPX/SPX, DecNET, etc. Further, some gateways only worked with the same vendor's companion emulators, giving I/S solution providers little flexibility in vendor and/or cost choices. If you needed lots of sessions, you bought lots of gateways and spent lots of money. Figure 3 illustrates typical early gateway approaches of LAN-to-SNA connectivity.
Figure 3
The gateway approach has tremendous merit when considering the needs for LAN-to-SNA connectivity. As mentioned in the introduction, it has been virtually impossible for MIS to dictate across large, relatively flat organizations exactly which network types and computing platforms will be used. The management paradigm seems to have been to give departments purchasing autonomy and then have centralized I/S administer and maintain the resultant purchases. This has lead to organizations that employ a wide variety of network protocols and hardware types to conduct daily business. The problems for I/S are to provide mainframe access for this variety of non-SNA networks and to maintain security, provide high capacity and high performance, while using a connectivity platform that is proven and therefore has a high comfort factor. The Bus-Tech 3172-NT meets those requirements by integrating several products into one unique "enterprise ready" package. By combining SNA gateway technology from Microsoft with IBM Channel technology from Bus-Tech with physical network connectivity from IBM, Bus-Tech is at the leading edge of the evolution of multi-protocol LAN-to-SNA integration.
The Bus-Tech 3172-NT combines technology from three vendors to yield a unique, high performing LAN-to-SNA host solution. The three vendors and their integrated components within the Bus-Tech 3172-NT are:
Each of these components will be described to provide a complete understanding of the 3172-NT. Because the basic evolution of gateways has been explained, let's start with the features and benefits of Microsoft SNA Server.
SNA Server's client-server architecture allows for transport-independent host access using all popular LAN protocols.
Microsoft SNA Server is a LAN-to-SNA gateway that provides SNA communications for LAN-based services and multiple platform PC workstations running a variety of network protocols. SNA Server employs a client-server architecture that is tightly integrated with, and leverages the strengths of, Microsoft Windows NT Server. SNA Server can be configured as an IBM PU 2.0, PU 2.1, APPN LEN node or support a DSPU. LU services provided are LU 0, 1, 2, 3 and LU 6.2. SNA API support is comprehensive with the inclusion of APPC, EHNAPPC, CPI-C, CSV, LUA/SLI, and ODBC/DRDA. SNA Server also supports TN3270 through an included TN3270 server and provides for high speed file transfer through support via APPC File Transfer Protocol ( AFTP).
SNA Server allows for comprehensive, bi-directional SNA access while maintaining LAN protocol transport independence. All popular PC operating systems are supported including Windows NT Workstation, Windows®, Windows® for Workgroups, Windows 95, MS-DOS®, OS/2®, UNIX®, and Apple Macintosh®. Multiple network protocols including Novell IPX/SPX®, TCP/IP, Banyan® VINES® IP, Named Pipes, AppleTalk® and RAS are also supported.
The majority of large enterprises that employ mainframes and AS/400 systems generally possess a variety of LANs but do not use SNA gateways. Direct connection of PCs to mainframes and AS/400 systems remains the most popular connection scheme. Despite widespread acceptance, these approaches are expensive, waste resources on both ends, and are difficult to administer. The drawbacks of direct connections to SNA based systems are alleviated through the use of flexible and robust SNA gateways such as Microsoft SNA Server. SNA Server provides many significant advantages for the desktop user, LAN administrator and host administrator, when compared to connecting PCs directly to SNA host computers.
SNA Server increases stability, saves memory, and reduces complexity at the desktop by allowing the choice of only one protocol per desktop. In contrast, when connecting directly, the DLC (802.2/LLC) protocol is required for connection to the host, in addition to a LAN protocol such as TCP/IP , IPX/SPX, or Banyan Vines, to connect to the file/print/database/mail/systems management server on the LAN.
SNA Server is designed to provide easier administration, greater security, and configuration flexibility. When connecting direct, each desktop must be configured individually with the host's network address, LU name, and XID. Whenever there's a change on the host side, such as the XID is updated, all desktops must be reconfigured. In large organizations, where thousands of desktop systems need access to host applications, reconfiguration of large desktop populations can be an overwhelming task. With SNA Server, there's nothing to configure at the client; all host changes can be tracked centrally by the LAN administrator through the SNA Server Admin tool.
Branch configuration - SNA Server provides the host link for remote clients. No configuration is required at the client desktops.
SNA Server reduces the frequency of VTAM gen re-definitions, lessens host memory requirements, frees-up expensive host CPU cycles, saves network bandwidth, and provides more reliability than direct connect client configurations.
Centralized configuration - All host access is routed through SNA Server. SNA traffic is isolated to the data center while native LAN protocols are used on the corporate WAN.
Most enterprise environments include desktops running Windows, Windows for Workgroups, Windows NT Workstation, Windows 95, MS-DOS, Apple Macintosh, OS/2 and UNIX, with a networking mix that contains IPX/SPX, TCP/IP, NetBEUI, Banyan VINES IP, AppleTalk in addition to SNA protocols. IS directors wish they had a single solution to provide IBM mainframe and AS/400 data to every desktop. Corporate data on the host systems must be made available to users in the simplest and most efficient manner. The days of hard copy reports and hand keying of information back into disparate systems are long over. On-line access and the sophisticated integration of enterprise data offered by client-server technologies are demanded by end users.
Flexible SNA gateway and intelligent client solutions for today's heterogeneous environments.
Microsoft SNA Server provides the solution for this heterogeneous reality, while offering the extensibility demanded by the ever-changing computing environment. Large enterprises and small to medium organizations no longer have to worry about how users will access host data across the network today or tomorrow.
Microsoft SNA Server provides a single access method for all IBM host systems by solving the problem of mixing disparate LAN and SNA protocols on a single network. Due to SNA Server's extensive support for SNA and LAN protocols, in most cases LAN administrators do not have to make any changes to their current network structure. It fits right in. Whether organizations are using protocols such as TCP/IP or IPX or need to support Banyan VINES IP, AppleTalk, NetBEUI or remote dial-up clients, SNA Server can meet the challenge. SNA Server extends access to all SNA functions to all network clients through its protocol-independent client-server architecture. The result is desktop users can use their favorite host access product no matter which client operating system or networking architecture is currently in place or planned for the future.
Since SNA Server is an application integrated with Windows NT Server, it can grow with organizations as they increase the number of users connecting through the gateway, the number of host connections, or the types of applications that use gateway services.
SNA Server is also architected to take advantage of multi-processor versions of each of these systems. Running SNA Server on a multiprocessor system can dramatically improve performance in cases of high load or heavy traffic.
In any large IS environment, an individual gateway can be viewed as a single point of failure. For mission-critical use, Microsoft recommends a minimum of two SNA Servers to provide fault tolerance. Up to 50 SNA Servers can be grouped together to provide load balancing and hot backup, allowing sessions to be automatically rerouted to a backup gateway should the primary gateway or host link fail. The load balancing and hot backup features work both for mainframe connections and AS/400 connections-and both for dependent and independent LUs. For highest speed mainframe connectivity, SNA Server works with direct channel attached technology such as the Bus-Tech 3172-NT. This device can provide host access at speeds many times greater than the fastest direct LAN attachments.
A single Windows NT Workstation or Windows NT Server, located anywhere in the corporate network can configure and manage all of the SNA Servers in the network using graphical tools that are included with the product. If the servers reside at a central location, the IS staff can be responsible for the administration and monitoring of all host access. This can also be accomplished from the IBM host console because of the integration of SNA Server with NetView facilities.
For maximum acquisition and implementation flexibility, SNA Server licenses can be purchased using two different models.
Each of these models has specific advantages when implementing SNA Server solutions. The client based approach is more desirable in multiple server environments requiring extra capacity, load balancing or hot backup.
The IBM 3172 Interconnect Controller is an industry standard LAN-to-mainframe connectivity platform. Large organizations worldwide trust the 3172 with their daily mission-critical data. The 3172 supports up to two channel connections and any combination of up to four LAN adapters of various physical network types. These network types include Ethernet, Token Ring, and FDDI. The 3172-NT takes full advantage of the flexibility and reliability of the 3172 for implementation of Microsoft Windows NT Server and Microsoft SNA Server.
Bus -Tech has been providing physical network connections to IBM channel interface products for more than 10 years. In the case of the 3172-NT, Bus-Tech has optimized the channel interface software, or drivers, that are used in conjunction with their high performing Micro Channel-to-Channel Adapters (MCCA). Unlike competing products, the Bus-Tech MCCA's have on board processing capabilities designed to provide intelligence when communicating between the IBM host and the IBM 3172 backplane. The on-board intelligence handles the channel interrupt requests locally allowing the Pentium processor of the 3172-NT to focus critical resources directly on SNA Server processing. Further, the MCCA's provide 3.0 MB/S and 4.0 MB/S streaming mode data transfer between the 3172-NT and the IBM host. Data Streaming mode maximizes data transfer by minimizing the number of channel I/O requests per any given amount of data. The channel drivers used for configuring Bus-Tech channel connections are built into SNA Server 2.11 and are provided pre-loaded at the factory for the 3172-NT. By using the proven combination of Bus-Tech hardware adapters and microcode channel drivers in the 3172-NT, solution providers are assured maximum processing efficiency and compatibility between these key operating components.
As mentioned previously, the Bus-Tech 3172-NT is a unique and powerful combination of reliable, high performance and high capacity components. The 3172-NT provides the highest possible interface bandwidth by being at the junction of the two highest speed access points for this type of connectivity - the network and the IBM channel. In addition, the unit has very high reliability and is installed and serviced by IBM.
Figure 4
Figure 4 displays the components of the 3172-NT. Up to two Bus-Tech channel adapters can be installed in the 3172-NT for connectivity to multiple mainframes. Ethernet, Token Ring or FDDI adapters can be chosen for connectivity to multiple physical networks. The 3172-NT arrives at the customer site with pre-loaded Microsoft Windows NT Server, Microsoft SNA Server and the specified number of Bus-Tech channel adapters with driver software and requested network interfaces. After a quick installation by IBM Service Representatives, the unit is ready to operate as a direct channel-attached SNA-to-LAN communications server.
Figure 5
Figure 5 illustrates the flexibility of the 3172-NT and the SNA Server environment. There are several areas worth noting here.
The evolution of SNA host access and networking technology has lead organizations to employ a variety of networking solutions. Each network type has advantages and disadvantages, depending on hardware platforms, solution requirements and implementation. Portions of SNA have been optimized for certain uses. This is proven by the fact that there is no more efficient and integrated network software on a mainframe than VTAM. TCP/IP is optimized for UNIX machines and its role for other systems is increasing. Banyan VINES, Novell IPX/SPX, and Microsoft NetBEUI have attributes that make them appropriate for specific purposes. Organizations should not be penalized for choosing a variety of network protocols to meet their enterprise computing needs. The product combination that is embodied in the Bus-Tech 3172-NT removes the traditional barriers to mainframe and AS/400 access that have existed simply because of multiple network protocol types. The 3172-NT brings these divergent network types together in a cost-effective, flexible, high-performing, and standardized manner.
For more information:
Contact your local Microsoft office or a Microsoft Solution Provider near you. In the United States, call (800) 426-9400 for product information or to locate a Microsoft Solution Provider. In Canada, call (800) 563-9048. Outside the United States and Canada, call your local Microsoft subsidiary or (206) 936-8661. Via the Internet, use: http://www.microsoft.com.
BUS-TECH, Inc. :
129 Middlesex Turnpike
Burlington, MA 01803
(617) 272 8200
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