Server-Based Routing - Windows NT Internetworking

Archived content. No warranty is made as to technical accuracy. Content may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist.
By Charles Machalani, Senior Program Manager, Microsoft Servers Business Unit

Eicon Technology Corporation

1st Quarter 1997

We at Microsoft Corporation hope that the information in this work is valuable to you. Your use of the information contained in this work, however, is at your sole risk. All information in this work is provided as is, without any warranty of its accuracy or completeness, and none of the third-party products or information mentioned in the work are recommended, supported or guaranteed by Microsoft Corporation.

On This Page

The Network Operating System (NOS)
Enterprise Networking or "Internetworking"
The Enterprise Network Operating System
For More Information


Eicon Technology is in the business of connecting people to information. Our goal is to facilitate access to information wherever it resides. Microsoft Corporation is the worldwide leader in software for personal computers. Microsoft Windows NT is considered the preferred, open client-server application platform Network Operating System (NOS) available because of its hardware independence.

For the last decade, the corporate network infrastructure has evolved to accommodate the computing needs of users. Electronic information today resides in many locations other than the host computer or corporate LAN. Connecting all these remote resources and users together has led to what is known as the "Networked Enterprise."

With the network constantly evolving, and the emphasis now on the Wide-Area Network (WAN), a need greater than ever has developed for Enterprise-wide Network Operating Systems. These NOSs integrate all LAN-WAN internetworking with application computing. For many years, the NOS has been connecting people to the LAN. The Enterprise NOS, however, will extend that capability and connect people to information world-wide.


Due to the incredible growth in the use of personal computers after the mid '80s, companies moved away from traditional host-based hierarchical information systems and migrated towards truly distributed client-server environments. These PCs produced a tremendous amount of new, local information and almost overnight MIS managers needed to develop ways to integrate the host-based data with local information and applications.

What was required was transparent access to information, regardless of its location. Another requirement was sending SNA, IPX/SPX and TCP/IP data down the same leased line. As a result the multi-protocol router was born in the late '80s. These routers opened the door permitting different types of protocols to be transmitted on the same wire and set the stage for a quantum leap in the development of the networked enterprise.

This white paper discusses how Network Operating Systems evolved within the past two decades. It also identifies the changes and the benefits behind an enterprise-wide NOS-based internetworking environment.

The Network Operating System (NOS)

In the 1980s, the NOS successfully defined, structured and used local area networks. It supplied basic file and print sharing services to users on the LAN. In other words, the NOS connected people on a LAN.

During the late 1980s, corporate restructuring created the need for new productivity tools capable of better serving the new "distributed computing" infrastructure. These tools, such as e-mail, workgroup computing, workflow automation and distributed databases became the everyday working tools of major corporations. As a result of these changes, the NOS evolved and the connection moved from the local-area network (LAN) to the wide-area network (WAN).

We have evolved to the point where individual desktops are connected to local-area networks, to wide-area networks and to mainframe computers or application servers. This is what we call "Enterprise Networking" or "Internetworking".

Enterprise Networking or "Internetworking"

With the proliferation of LAN to WAN technologies came the advent of client-server computing, a decentralized computing paradigm, which offers interactive real-time sharing of information. Client-server computing or "distributed computing" was made possible through the development of router internetworks that could dynamically connect and route data between LANs.

Although a range of LAN protocols could be routed, TCP/IP slowly emerged as the defacto internetworking protocol due to its open standard. This open standard, however, led to different implementations of IP-based solutions and consequently created the need for interoperability for enterprise-wide networks. Today, interoperability has become an essential part of the networking infrastructure.

Systems are internetworked through existing and emerging corporate backbone architectures to a variety of internal and external connections (nodes). Users attach their computers to LANs either locally or remotely via the corporate backbone. Remote nodes provide remote users the same privileges, and access to applications as if they were locally attached to the LAN. As corporations connect more and more remote sites, their operations must expand into enterprise-wide solutions that combine networking with applications. Network operating systems must ensure this integration if remote users are to benefit from true client-server environments. This is the new era of the Networked Enterprise; an infrastructure built around the concept of location-independent access to information.

In order to fully understand the Networked Enterprise and the benefits of Server-based Internetworking, let's first review some basics about how information is accessed, and how the routing process works.

How information is accessed

The table below cross-references hardware devices required to access information:

When routing is needed

A router is installed

When remote access is needed

A remote access device is installed

When SNA connectivity is needed

An SNA gateway is installed

When OSI Host access is needed

A modem sharing device is installed

When proprietary communications is needed

A specialized communication card is installed

When X.400 e-mail is needed

An X.400 gateway is installed

Whether it's LAN-to-LAN wide area networking, Remote LAN access or Branch LAN to SNA connectivity, network managers must make several choices when considering their options for connecting people to information. They will need to first identify the most cost-effective WAN medium (POTS, PPP, Frame Relay, ISDN or X.25) available. Depending on their choice, or availability, they will then have to choose the appropriate hardware interface, or WAN interface adapter, to establish the connection to the WAN. Once they are connected, they will need to choose the application(s) to share the data.

This procedure is required for every connection on the networked enterprise. Imagine if the connection is different for most of the users. There would be a huge number of hardware devices and software requiring integration. It would be a nightmare to manage all of these connections.

Understanding the Routing Process

A router helps LANs and WANs achieve interoperability and connectivity. Each packet sent over a LAN has a header that contains source and destination address fields to indicate where the packet originated from and where it is going. Routers connect LANs or WANs together while optimizing network performance. For example, for a packet to go from computer x to computer z in the following illustration, the best route uses only one hop. If Router 1 is the default router for x, the packet will be re-routed through Router 2, and computer x will be notified of the route to use to get to computer z.


A sample routing process

In short, the router facilitates the exchange of routing information. Routing can be performed either by a computer (software-based or server-based routing), or by an independent piece of hardware better known as "hardware-based or box-routers". Hardware-based routers are self-contained with an integrated LAN and WAN interface.

Routers are good at what they do route information. Routers rely on their own OS to control and manage them. They are not designed to integrate with client-server applications. The software-based router or NOS-based router is a branch server equipped with a Network Operating System capable of handling packet and router processing. The NOS-based router is the result of the natural evolution of a Network Operating System combining client-server applications with communications.

Whatever the connection, Remote LAN access, LAN-to-LAN wide-area networking, Branch LAN to SNA connectivity or all of the above, the evolving "Enterprise NOS" is now the central point to connecting people, applications and information world-wide.

The next section introduces Microsoft's Windows NT, an enterprise-wide NOS with WAN capabilities.

The Enterprise Network Operating System

Not too long ago, two major network operating system suppliers added embedded routing to their NOS setting the stage for yet another industry change: Novell's NetWare and Microsoft's Windows NT. With this capability, routing comes part and parcel with their NOS. The responsibility of assuring interoperability and network management has become a system function. The Server-based routing or NOS-based routing allows network managers to connect LANs together or LAN-to-WAN without needing to purchase a dedicated router.

By installing Windows NT Server Multi-Protocol Routing service and enabling the Routing Information Protocol (RIP) routing options, the Windows NT Server is able to route network packets between two or more network adapters using RIP on Internet Protocol (IP) or Internetwork Packet Exchange (IPX) or both. In addition, installing a WAN interface adapter (WAN NIC) to the server, routing between WANs over switched circuits or dial-up lines (e.g. T1 or Frame Relay) becomes possible. As WAN requirements grow, new software, new adapters, and/or new server hardware can be added to meet evolving needs. Server-based wide-area networking is the logical approach to branch office connectivity.

Understanding the WAN Interface Adapter

Not all WAN interface adapters are created equal. Currently, NOS-based schemes require the use of either a passive WAN NIC or an active WAN NIC to enable LAN-to-WAN-to-LAN routing. Passive adapters rely totally on the host CPU to process and send packets over the WAN. In many ways, this is similar to the way a LAN adapter is used for the LAN. These adapters were designed as high volume packet forwarding engines. They are designed for low protocol overhead router applications, such as PPP, using the NOS protocol stack and routing algorithms.

An active or intelligent WAN adapter, on the other hand, uses its onboard CPU to perform this function. This type of adapter is needed when complex protocols such as X.25 are used, when data compression is needed, or when multi-protocol support is required. In this case, frames are sent directly into system memory through the bus, bypassing the server CPU, and processing all protocol stacks using the adapter's CPU. Some of these adapters come with flash memory, allowing storage of multiple protocol modules and a default bootable configuration. These protocol modules may include Frame Relay, ISDN, PPP, HDLC, SDLC and/or X.25. Flash memory becomes beneficial after the initial installation, especially when an adapter is removed from one PC and installed into another. The need to repeat the configuration process is no longer necessary thus enabling branch office maintenance or upgrades.

The following diagram illustrates a typical configuration connecting to a central/corporate network through PDN and dial-up ISDN services:


The Advantages of Server-based Internetworking

This section outlines some of the advantages of a server-based internetworked branch office configuration.

Consider the remote office configuration illustrated above. Two branch offices, located anywhere in the world, require communication through the corporate backbone to access data on the LAN and on the SNA Host. These branch offices are using Microsoft's Windows NT BackOffice Server applications and Microsoft's Office productivity tools. To add complexity to our problem, the offices use different carrier services.

Typically, the network manager would have to purchase a router to perform the routing functions required, a remote access device for LAN access and modem pooling and an SNA gateway for host access. The network manager, based at corporate headquarters, must ensure interoperability between all of these devices and the entire network, compatibility between applications and overall control of communication costs since line prices constantly keep changing. So when evaluating carrier service networking equipment for remote offices, network managers have learned to ask the right questions

Will I get the most out of my WAN bandwidth?; Is it compliant with all relevant standards, especially for interoperability and congestion management?; How scaleable is this solution?; How easy and complete is the remote management?.

Some other questions, regarding application software, allows network managers to evaluate how that information is to be accessed.

What type of information do I need to access?; What software am I going to use and do they integrate well with each other?

Growth is inevitable on both the LAN and the WAN and planning for growth is essential. Therefore, when implementing a branch office solution it makes sense to ask: Is it possible to add a WAN port (or two) to my router, and at what cost? or Can I change my carrier service from X.25 to Frame Relay?, or to ISDN?, etc. if prices change.

A simple change, such as adding a WAN port at a remote site or a change of communication services should not require the network manager to replace the entire router. Of course, for a branch office, versatility is considered a huge advantage.

So there are a number of important factors MIS and Network Managers must consider when choosing the NOS, the application software, and the internetworking infrastructure needed to communicate on the WAN. This is what makes server-integrated routing or NOS-based internetworking advantageous for branch office environments.

Microsoft Windows NT has the breadth of protocols and services to integrate all of the above into an easily manageable system. It integrates with NetWare, LAN Manager, UNIX, DECnet, SNA and other network systems through its network foundation. Some of the services supplied are Remote Access (RAS), TCP/IP, NetWare, and Host Connectivity. But alone it cannot accomplish true integration. The need for a WAN interface adapter, performing LAN emulation, is required to accomplish seamless communications integration.


Network integration is a very complex issue. Network planners are constantly looking for ways of integrating client-server applications with enterprise-wide networks. However, in the interest of controlling costs, network administrators are often faced with the requirement of making difficult choices. Choices that are based on flexibility, adaptation to changing technologies and evolving needs.

Eicon Technology and Microsoft continue to work together in an effort to ensure that Windows NT customers remain recipients of cutting-edge and scaleable technology. Eicon continues to refine the power and speed of its Wide-Area Networking hardware and software, while Microsoft is seeking to deliver more power and ease-of-use by further extending its Wide Area Networking services. By combining these technologies, network administrators achieve an easy-to-implement, cost-effective branch-office solution, resulting in a low cost-of-ownership. It is a simple, all-in-one solution that integrates client-server applications with communications, ensures compatibility and interoperability throughout the network, and protects their investment from obsolescence.

Eicon Technology Solutions

Let's look at how Microsoft's Windows NT uses Eicon Technology's WAN adapters to enable wide-area networking.

Eicon Technology has been providing networking solutions for over a decade. Eicon Technology offers a wide range of WAN adapters that meet varying needs. Eicon WAN interface adapters are classified as Passive WAN adapters, Intelligent Multi-service WAN adapters or ISDN adapters. They are also grouped by classes which are defined in accordance with the application and product intent.

Eicon passive WAN adapters, or P-class adapters, do not perform any protocol processing. These adapters offer the highest performance of any adapter for leased line connections using PPP or SDLC.

Eicon ISDN adapters, or DIVA adapters, are available with different combinations of ports and ISDN connection types. Server-based ISDN adapters handle all ISDN protocol processing.

Eicon intelligent WAN adapters, or C-class and S-class adapters, such as the C21 and S51, perform all WAN protocol processing onboard. They support a wide range of connections including Frame Relay, PPP, SDLC, X.25 and ISDN. This makes them ideal for applications involving multiple WAN media; for example, a high speed permanent connection with ISDN backup.


ISDN Backup on Multi-service Adapters

Eicon Technology's Very High Speed Serial Interface (VHSI) WAN adapters offers a "smart cable interface" which informs the card of the type of interface in use. The physical interface selection that these adapters support are V.24, X.21bis, V.35, X.21. This implementation eliminates the need for user intervention or a manufacturer pre-configured board with one physical interface limiting the user's ability to evolve or change. These adapters are truly versatile. They support multi-service and multi-protocol WAN environments.

Eicon Technology's intelligent WAN adapters integrate seamlessly with Microsoft Windows NT, Microsoft BackOffice Server applications and Microsoft Office productivity tools. They can migrate from one WAN medium to another. Furthermore, they can handle multiple protocol stacks concurrently and they are certified on all four hardware platforms that Windows NT supports (Intel, MIPS, Alpha and PowerPC ).

Eicon Technology's intelligent WAN adapters are the only adapters to extend Microsoft's IP stack across a Wide-Area Network via Frame Relay, PPP, X.25 and ISDN. Eicon Technology's WAN services have obtained complete certification and endorsement from Microsoft. They have obtained the "Designed for Microsoft BackOffice" logo and the SNA Server companion guide certification. Eicon WAN adapter software drivers are fully certified and listed in Microsoft's Hardware Compatibility List. A complete set of Eicon WAN adapter drivers will be supplied with Microsoft's next major release, Windows NT v4.0.

For More Information

Both Eicon Technology and Microsoft offer additional information about Wide Area Networking hardware and software.

For online information relating to Eicon Technology WAN adapters and product bundles, access the Eicon Technology World Wide Web homepage at

For information about Microsoft Corporation in the U.S. call, (800) 426-9400.

In Canada call, (800) 563-9048 and outside the U.S. and Canada, call (206) 936-8661.

For online information about Microsoft software, access the Microsoft World Wide Web page at