SIMATIC NET Network Management White Paper 11/2001 Netzwerkmanagement
Objective: The purpose of this White Paper is to provide information on the subject of network management in automation and indicate how this topic will develop in the future. In addition to the basic technical and financial considerations, apects such as: Considerable simplification of plant diagnostics and plant operation Short commissioning times Low maintenance costs Increased operational safety and reliability Shorter and fewer downtimes Improved plant availability are also of interest when deciding to implement network management. This symbol indicates a reference to SIMATIC NET products or special SIMATIC NET solutions Published by SIEMENS AG Group: Automation and Drives Division: SIMATIC NET Industrial Communication P.O. Box 4848 90327 Nuremberg Further assistance: Any inquiries can be addressed to your contact at your local office. You will also find SIMATIC NET on the Internet at http://www.ad.siemens.de/net Copyright AG 2001 All Rights Reserved Page 2 of 23 Excellence in
Objective:...2 Introduction...4 Task range of network management...4 Configuration management...4 Error management...4 Performance management...5 Security management...5 Account management...5 Network management with SNMP...6 Function...6 Communication procedure...7 Management Information Base - MIB...8 Network monitoring with RMON...8 Management station Network Manager & Web-based management...9 Network Manager...10 Web-based management...10 Further development of SNMP...11 Network management for industrial networks...12 Signalling concept...12 Network management based on SNMP and RMON...13 Web-based management...13 SNMP OPC server integration of network management in industrial networks...15 Summary...17 Forward look at network management at SIMATIC NET...20 Glossary...21 Copyright AG 2001 All Rights Reserved Page 3 of 23 Excellence in
Introduction The concept of network management was born at the beginning of the 1980s when the Internet age began. At that time, the situation was one of constantly growing networks using a wide variety of components from different manufacturers. The question was how to monitor and administrate these heterogeneous network structures. This problem was solved in the 1980s when the Internet Activities Board (IAB) introduced the Simple Network Management Protocol (SNMP). This standard, which was soon accepted throughout the network industry, fulfilled the basic tasks of a network management system. Meanwhile, the situation that once affected the office world has reached automation as well. With more and more distributed structures and a steadily increasing level of networking, the importance of network management in industrial networks is also on the rise. This is primarily due to increased vertical integration, a term used to indicate the merging of industrial networks and office networks. This White Paper discusses the various basic tasks performed by network management, explains underlying mechanisms and protocols, and shows different approaches to automation-specific solutions. Task range of network management Network management is subdivided into the following tasks. Configuration management Configuration management comprises the collection, presentation, control and updating of configuration data. This includes, for example, the configuration data of individual ports of a network component or the communication relationships between network components. Error management The purpose of error management is to increase the availability of the network. Errors must be detected as early as possible before they cause breakdowns in the network. Error management also ensures faster error diagnosis and fault repair. Copyright AG 2001 All Rights Reserved Page 4 of 23 Excellence in
Performance management Performance management monitors a network's performance. For this purpose, network load data are collected over certain periods, making it possible to display the time-related progression of the network load. This allows a constant evaluation of the network load and an early recognition of potential bottlenecks, thus making it possible to plan network expansions well in advance. Security management In security management, passwords and access permissions are assigned for a data network and its resources. Unauthorized accesses must be detected and gaps in the security system must be closed. Account management Account management is used to record cost shares within a network. These costs can then be charged to the individual users in accordance with traffic levels. Almost all the network management tasks mentioned above are assuming increasing importance in automation as well. Configuration management and error management, which today are still solved primarily using proprietary tools and protocols from different system manufacturers, represent the primary tasks of network management in automation. Performance management and security management are also gaining importance. The advantage of performance management in industrial environments with static networks particularly appears in the commissioning and expansion phases. Thus it is possible to design and dimension plants rationally and efficiently. With accelerating vertical integration, security management is also becoming more important. Account management, however, plays virtually no role in automation. Copyright AG 2001 All Rights Reserved Page 5 of 23 Excellence in
Network management with SNMP Function SNMP - Simple Network Management Protocol is a UDPbased protocol especially designed for administration of data networks. Meanwhile SNMP has been established as de facto standard for TCP/IP devices. The individual nodes in a network network components as well as data terminal equipment have a so-called SNMP agent, which makes information available in structured form. This structure is called MIB (Management Information Base). The agent is an integrated software application within the network node. A SNMP-based network management solution operates in accordance with the client/server model. The management station (SNMP client) can request information from the agents, which operate as servers. Typical SNMP client applications are Network Manager or Web-based management. SNMP Client S imple N etwork M anagement P rotocol - Network Manager - Web-based management GET GET NEXT GET RESPONSE SET SNMP Agent M anagement I nformation B ase TRAP Figure 1: Communication link between SNMP client and SNMP agent Copyright AG 2001 All Rights Reserved Page 6 of 23 Excellence in
The MIB information is called up and displayed by the management station cyclically or on an event-controlled basis. However, the nodes are also capable of suppling the network management station with certain status information using socalled traps without having received a request for that information. SNMP not only makes it possible to monitor the nodes, but also to control them, for example an instruction to activate or deactivate a port of a network component. Communication between agent and network management station executes as background task, and only puts an insignificant load on the network. Communication procedure SNMP builds on the link-free UDP (User Datagram Protocol) protocol, in which data interchanges are not acknowledged. In order to read out an SNMP variable, the management station sends an initial get request to the agent of the unit being addressed. A get-next request can be used to read in follow-up data. The agent replies to these requests with a response message. The management station can change the current configuration of a managed unit by sending a set message. Devices can inform the management station of status changes on an event-driven basis. This can be done by sending a trap message. SNMP Client UDP IP Network Layer SNMP Messages SNMP Agent UDP IP Network Layer Figure 2: SNMP communication path Copyright AG 2001 All Rights Reserved Page 7 of 23 Excellence in
Management Information Base - MIB A MIB (Management Information Base) is a standardized data structure consisting of various SNMP variables written in a target system-independent language. Thanks to cross-vendor standardization of both MIBs and access mechanisms, it is possible to monitor and control even a heterogeneous network with components from different manufacturers. Some examples of standard MIBs which have been defined to date: Bridge MIB RMON MIB MAU MIB... If component-specific, non-standardized data are required for network monitoring, they can be described by the manufacturers in so-called private MIBs. It is thus also possible to request values that have not yet been standardized. Network monitoring with RMON The RMON standard (Remote Monitoring Standard) is an extension of SNMP, and plays an important role in network management. RMON makes it possible to make selected, edited network data available. These data include the percentual load on individual ports, fault statistics, and the type and number of telegrams transferred. These values provide information about the network load, and are used to detect bottlenecks and to take early decisions about necessary network expansions. RMON enables the distributed collection and statistical compression of traffic data. The data are collected using special SNMP agents called RMON probes. Due to the large amount of memory and high level of performance required by RMON, in the past these RMON probes were often designed as standalone network components. Due to the growing performance capabilities of network components in general, this functionality is now often integrated in switches. As is the case with SNMP, the variables required for remote monitoring are standardized in special RMON MIBs. Copyright AG 2001 All Rights Reserved Page 8 of 23 Excellence in
Management station Network Manager & Web-based management Typical SNMP client applications include Network Manager and Web-based management. Both solutions make it possible to monitor and administrate a network from a single central location. The computer on which the application executes is called management station. Network Manager or Web-based management 100Mbit/s RM 100Mbit/s 100Mbit/s... 10 MBit/s Internet RLM Network Manager or Web-based management with MOBIC Network Manager or Web-based management via WAN for remote administration Figure 3: Central monitoring and administration of a network with Network Manager or Web-based management Copyright AG 2001 All Rights Reserved Page 9 of 23 Excellence in
Network Manager Network Managers are available in a wide variety of versions and price categories. Basically, a distinction is made between so-called platform solutions and so-called enterprise solutions. Platform solutions normally provide simple network management for network nodes, and are often adapted to the product line of the respective manufacturer, that means, the manufacturer also supplies the Network Manager. Typical functions are displaying and monitoring of the network infrastructure as well as the analysis and optimization of network traffic. So-called device views enable graphical representation of the management objects in the management system. If there is no device view for the respective component, the objects are displayed on a line-by-line basis via a so-called MIB browser. Examples of platform solutions are Spectrum from APRISMA Managment Technologies (formerly Cabletron) and SunNetManager from Sun Microsystems. In the case of enterprise solutions, various device platforms are usually integrated in the basic version or are available as options. In addition, enterprise solutions enable control of important business processes within a company, such as software distribution, application management and memory management. Typical enterprise solutions are HPOpenView from Hewlett-Packard, Unicenter TNG from Computer Associates and Tivoli from IBM. Web-based management In contrast to a Network Manager, Web-based management is not used to control and monitor an entire network, but only a single network component, data terminal or network cluster. Only a standard Internet browser such as Netscape Communicator or Internet Explorer is required. Browser technology enables access from different operating system platforms, such as Windows XP or UNIX. The familiar look and feel of the browser supports a quick start with network management with little training. The network nodes are accessed, for example, using an applet, which is normally loaded directly from the device using a browser. This applet dynamically accesses the SNMP variables in the addressed modules and displays them graphically on the browser. Web-based management offers a simple, low-cost entry into network management. In addition, the Web-based management supplied by the device can be integrated relatively easily in a Network Manager, and is thus independent of the system environment. Copyright AG 2001 All Rights Reserved Page 10 of 23 Excellence in
Further development of SNMP Version 1 of SNMP was originally developed as a simple temporary solution until a network management system based on the OSI standard could be completed. Because of its quick acceptance on the market, it became, in contrast to OSI network management, the de facto standard. However, Version 1 contains a number of features to be innovated. In addition to unacknowledged data transmission, these include the fact that passwords and management information are transmitted unencrypted over the network. Moreover, no mechanisms exist to guarantee the integrity of the transmitted data. In order to solve these problems, a revised version of the SNMP protocol was approved and released in the mid 1990s. Called SNMP Version 2, it was not used by manufacturers and thus failed to gain wide market acceptance. At the end of the 1990s, the SNMP protocol was revised again. The objective was a practical SNMP protocol which would be accepted by all manufacturers, and it was called SNMP Version 3. The new features of SNMP Version 3 included new commands such as GetBulkRequest, which allows to obtain multiple variables from an agent with a single request. This packaging reduces the network load caused by management messages. SNMP Version 3 also enables distributed network management. This allows the management system to be subdivided into small, compact units which monitor sections of a large network, permitting network management at the department or building floor level. Also new in SNMP V3 is that several agents can be referenced under a single IP address, making it possible for agents to monitor not only hardware components but also software components. In addition to these features, encryption mechanisms and time stamps were defined in the SNMP message to protect data and passwords. Access protection is provided through authentification by means of public and private keys. SNMP V3 has now been approved as draft standard, and initial reference implementations have already been demonstrated by a number of manufacturers. Further information on the progress of SNMP V3 standardization is available on the Internet at www.snmp.com. Copyright AG 2001 All Rights Reserved Page 11 of 23 Excellence in
Network management for industrial networks For some time now more widely distributed solutions and the increasing need for communication in industrial networks bring along the trend toward bigger and bigger network structures. With this increasing degree of networking comes a correspondingly strong demand for administration mechanisms which allow easier, more sensible handling of the more and more complex networks. In automation in particular, care must be taken to use a graduated solution concept, as industrial facilities can include anything from simple plants with a little networking to immensely complex industrial production lines. Even the meaning of vertical integration can vary from plant to plant. In addition, seamless integration in the existing control infrastructure is often required. This is normally implemented in the form of HMI/SCADA systems (Human Machine Interface, Supervisory Control And Data Aquisition, e.g. WinCC). As a result, different solution approaches are necessary, depending on the management task to be accomplished: Signalling concept For simple network management tasks SNMP agents in network nodes Vertical integration through integration in Network Manager Web-based management Cost-efficient, device-specific management for integration in heterogeneous system landscapes SNMP OPC server Integration of network management in industrial networks Signalling concept Since the introduction of the OLM rail-mounted star coupler from SIMATIC NET the signalling concept for Industrial Ethernet network components has been proved efficient. Via a so-called signalling contact, the network components provide a group signal that is used to monitor different states. With the aid of an input module, this signal can be forwarded for example to an HMI/SCADA system for visualization, enabling localization and elimination of network disruptions. The signalling concept provides a reliable, adequate monitoring system for small and medium-sized networks. No special knowledge of network management is required. Copyright AG 2001 All Rights Reserved Page 12 of 23 Excellence in
In addition to a signalling contact, the OSM BC08 also provides signal inputs for reading signalling contacts of other devices or monitoring for example door contacts or temperature sensors. This information is made available in the form of SNMP variables and is also integrated in the OSM BC08's Web-based management. In the future, all new members of the OSM/ESM product family will support this functionality. Network management based on SNMP and RMON The signalling concept described above does not always offer an ideal network monitoring solution for industrial networks which span large company sites and are linked to office networks. Moreover, input modules, which can read these digital signals, are not always available. SIMATIC NET offers SNMP-based network functionality for all its Industrial Ethernet network components, such as OSM/ESM (Optical Switch Module / Electrical Switch Module), RLM (Radio Link Module) and ELS (Electrical Lean Switch). The OSM/ESM contains additional traffic data for network monitoring in the form of RMON probes. These devices can therefore be managed, monitored and diagnosed from a central location using any network management tool on the market, thus allowing the industrial network to be incorporated in the office world (vertical integration). Web-based management SIMATIC NET offers Web-based management for network administration and diagnostics as a low-cost entry to network management within its switch modules. The OSM/ESM Web-based management graphics interface is divided into three areas: the device status field the menu tree window the data window. Copyright AG 2001 All Rights Reserved Page 13 of 23 Excellence in
The current LED indicator settings of the switch are shown in the device status field. While the four possible port LED states on the switch are selected using pushbuttons, the device status field provides all information at a glance. The menu tree is similar to a file manager, and helps the user navigate through the selected switch's diagnostic and control functions. The data window then shows the functionality selected in the menu tree window. These three areas make it possible to read out all important information regarding the switch or to make the necessary network settings. Web-Based management for SIMATIC NET provides a variety of information, even the visualization of some RMON statistics is integrated. As an example, the menu tree window in the Figure below shows the OSM/ESM status. Device status Menu tree Data window Figure 4: SIMATIC NET OSM/ESM network management interface Copyright AG 2001 All Rights Reserved Page 14 of 23 Excellence in
SNMP OPC server integration of network management in industrial networks HMI/SCADA systems such as WinCC have established themselves as successful tools for controlling and monitoring automation processes. One thing which systems from different manufacturers have in common is OPC (OLE for Process Control), a standardized, open, vendor-independent interface used in industry and automation. OPC provides access to different bus systems and protocols. In SIMATIC NET, these are the FMS/DP/S7 protocol, S5-compatible communication, and PROFInet. In addition to HMI/SCADA systems, OPC clients include Visual Basic and C++ applications and Microsoft Office applications. As already mentioned, SNMP is the de facto standard for managing TCP/IP nodes. In order to attain a network management solution that is embedded in the automation landscape, it is thus necessary to create a link between SNMP and OPC the SNMP OPC server. SIMATIC NET will offer this product starting at the fall of 2002. - HMI/SCADA - Visual Basic - Microsoft C++ OPC Client SNMP/OPC Server } OPC Server SNMP Client SNMP Agent M anagement I nformation B ase Figure 5: Functionality of the SNMP OPC server Copyright AG 2001 All Rights Reserved Page 15 of 23 Excellence in
The SNMP OPC server allows access to SNMP-compatible devices in all OPC client systems. This includes both read and write access to information, thus enabling diagnosis of everything from individual devices to complete systems as well as active control of device characteristics. Predefined device profiles and ActiveX controls are provided with the server and enable fast, easy system diagnosis in OPC client applications without special knowledge of the SNMP protocol. Customized expansions are also possible. The SNMP OPC server is an integral component of the SIMATIC NET OPC server, and thus provides the complete OPC infrastructure, such as OPC Scout for browsing through the SNMP information, as part of the standard package. The SNMP OPC server can be operated together with other PROFIBUS and Industrial Ethernet protocols such as PROFInet or S7 communication. As a result, existing HMI solutions can be expanded to include SNMPbased management functionality. The SNMP OPC server also has multi-client capability. Figure 6: WinCC example, that displays and monitors a network infrastructure using the SIMATIC NET SNMP OPC Server Copyright AG 2001 All Rights Reserved Page 16 of 23 Excellence in
Device information displays can be customized to meet the requirements of the customer s application. In addition, the information provided can be incorporated in the event signalling and archiving system of an HMI/SCADA system. The SNMP OPC Server enables network visualization, topology display, system diagnostics and plant status monitoring in any OPC client system. This means: Expanded device diagnostics Easy, precise fault/error localization Fast limitation of damages and error repair Increased operational safety and reliability as well as improved plant availability. In addition, the information made available via RMON can also be displayed and evaluated, thus enabling Displaying of load statistics and network traffic Monitoring of threshold values and localization of bottlenecks Effective planning of network expansions. Based on the SNMP OPC server an existing HMI/SCADA system easily can be extended with network management services and therefore becomes a plant-specific Network Manager. A separate Network Manager is not necessary any more. Summary The signalling concept with signalling contact is a safe, reliable and adequate monitoring system for small and mediumsize networks. Signal inputs allow the signalling contacts of other devices to be integrated in network management. When detailed information from different network nodes is required, SNMP agents in the network devices are the optimum solution. Step by step the SIMATIC NET Industrial Ethernet devices are being equipped with SNMP agents. These SNMPcompatible devices can be monitored by Network Managers, Web-based management, or via SNMP OPC server in HMI/SCADA systems. For choosing the right network management solution there are no standard rules to follow. The decision strongly depends on the relevant system environment. Copyright AG 2001 All Rights Reserved Page 17 of 23 Excellence in
Network Managers are normally used by experienced network administrators. The various features offered by a Network Manager are not always self-explanatory, and often require even an experienced specialist, who has very detailed knowledge of SNMP. This of course poses the question of exactly when it is advisable to use a Network Manager. The use of a Network Manager is always recommended when it is already part of an existing office infrastructure. In this case a specialist of the office network department can be used for monitoring the network. However, a process must be created, in which network administrators from the office environment and plant operators from the automation sector work closely together to ensure a fast exchange of information. The opening of the production sector to the office sector, however, sometimes brings safety risks due to purposeful or accidental access in production resources and thus in the production process. An appropriate safety barrier should be considered The advantages of a Network Manager specially acquired for the automation system depend above all on the qualifications of the operating staff and on the total costs of the network management. The latter applies in particular if the costs of a Network Manager solution is compared with an integration of network management services in a possibly existing HMI/SCADA infrastructure using the SNMP OPC Server. The calculation has to include the cost of adapting the Network Manager to the respective customer plant and any training that may be needed for the plant operator. Web-based management is a useful addition, above all for devices used in heterogeneous environments. It enables fast realization of the network management task without regard to, or as a practical supplement to existing management tools. Heterogeneous environments involve mostly network components, which is why all SIMATIC NET network components, or at least one representative of each product group is equipped with Web-based management. Due to steadily increasing performance capabilities and enhanced storage resources on the devices, Web-based management is also being used more and more in data terminal equipment. Copyright AG 2001 All Rights Reserved Page 18 of 23 Excellence in
Signalling concept SNMP agent SNMP OPC Server Network Manager Web-based management HMI/SCADAsystem Figure 6: SIMATIC NET solutions A solution optimized specifically for automation tasks is the integration of network management in OPC client systems with the SNMP OPC server. This solution fits in the existing plant situation, the established process sequences and the qualifications of the operating personnel. Network management based on the SNMP OPC server enables flexible adaptation to the customer's plant and processes. Whether signalling concept, SNMP agents for integration in Network Managers, Web-based management as cost-effective entry into network management, or SNMP OPC server for integrating network management in the automation task - SIMATIC NET offers suitable solutions for diverse needs and situations. This solutions complement one another, are coordinated with one another, and make network management almost in any system environment possible. Copyright AG 2001 All Rights Reserved Page 19 of 23 Excellence in
Forward look at network management at SIMATIC NET The integration of network management functions in HMI/SCADA systems thanks to the SNMP OPC server is an important step towards easy monitoring and maintenance of SIMATIC NET networks. In the future, additional efforts will be made to enable easy, application-oriented management of industrial facilities. In order to facilitate the administration of large industrial plants and networks, SIMATIC NET network components will not be the only components equipped with SNMP-capable management agents. Industrial Ethernet communication interface modules for SIMATIC PLCs and PCs will also have SNMP agents. The control of automation components in conventional Network Managers will be enhanced. In return, engineering tools such as STEP 7 and NCM will be equipped with some classic Network Manager functions. An integrated SIMATIC software and hardware landscape similar to TIA (Totally Integrated Automation) will be created on the one hand, and components from other manufacturers will be integrated step by step on the other. As a result, it will be possible to control and diagnose heterogeneous product landscapes from commissioning through control, monitoring and expansion. On this basis, successive upgrade from network management to system management is made possible, simply by introducing new services. These include, for example, system-wide software distribution, application management, memory management and maintenance management. Copyright AG 2001 All Rights Reserved Page 20 of 23 Excellence in
Glossary ActiveX Control Agent AUI Bridge MIB Client/Server model Device View DP ELS ESM FMS Full Duplex Half Duplex Heterogeneous network HMI/SCADA system IAB NCM ActiveX Controls are self-contained programs which can execute under Microsoft Windows operating systems. In addition to the executable program, these controls also have a graphics interface for control functions. ActiveX Controls can be developed in nearly any programming language. Software application which makes the station-specific data available to the management system. Attachment Unit Interface Special MIB containing SNMP variables for a bridge. A bridge is a device which connects two network segments with the same communication protocol at the Layer 2 level. In a computer network, a server makes data and services available to the clients. The terms "client" and "server" can be used to indicate a computer (hardware) as well as a computer program (software). Component-specific graphics module for the visualization of management objects in a network management system. Distributed peripherals (distributed I/O) Electrical Lean Switch, Industrial Ethernet switch with twisted pair connection system (FastConnect or RJ45) Electrical Switch Module; Industrial Ethernet switch with twisted pair connection system (D subminiature or RJ45) Fieldbus Message Specification Capability of a device to send and receive data simultaneously. In Full Duplex mode, collision detection is deactivated. A device can either receive data or send data, but cannot do both at the same time. Network with a wide variety of components from different manufacturers are referred to as heterogeneous networks Human Machine Interface, Supervisory Control And Data Acquisition. PC applications for controlling and monitoring processes in an automation system. Internet Activities Board Network and Communication Management, an engineering tool from SIMATIC NET Copyright AG 2001 All Rights Reserved Page 21 of 23 Excellence in
Network Manager MAU MIB MIB MIB browser Polling PROFInet OPC OSI OSM Private MIB RLM RMON RMON MIB RMON probe S5-compatible communication Typical SNMP client function. Interface to centralized network monitoring and administration. Special MIB. The MAU (Media Attachment Unit) establishes the link between a station's AUI port and the Ethernet medium. Management Information Base; database in a network component containing defined information about that component, such as status or statistical information An MIB browser makes it possible to display SNMP data on a line-oriented way. This is necessary when there is no graphics interface available to display management information. Cyclic scanning of information PROFInet is a specification from PROFIBUS International which defines a cross-vendor communication-, automationand engineering model. OLE for Process Control Open Systems Interconnection Optical Switch Module Industrial Ethernet network component with switch functionality; has fiber-optics and and twisted pair ports If component-specific, non-standardized data are required for network monitoring, these data, which cannot be described in SNMP standard MIBs, can be described in so-called private MIBs. Private MIBs are manufacturer-specified. Radio Link Module Access station (Access Point) used to establish radio cells and to serve as transition to a wired network. The RMON standard (Remote Monitoring Standard) is an extension of SNMP, and plays an important role in network management. RMON makes it possible to make selected, edited network data available. Special MIB with performance- and traffic data about the network Special SNMP agent for distributed collection and statistical compression of traffic data. Can be either a stand-alone device or integrated in a network component. The communication mode optimized for communication between SIMATIC S5 and SIMATIC S7 enables the migration of SIMATIC S5 to SIMATIC S7 via PROFIBUS and Industrial Ethernet. Copyright AG 2001 All Rights Reserved Page 22 of 23 Excellence in
S7 protocol SNMP TCP/IP TFTP server TIA Trap UDP Web-based management Communication functions integrated in the SIMATIC S7/M7/C7 CPU. The user calls these functions in the application program using SFBs (system function blocks). A configured connection is required. S7 communication is suitable for large volumes of data. It provides a networkindependent interface between SIMATIC S7/M7/C7 and PG/PC. Simple Network Management Protocol Standardized protocol for the transport of network management information Transmission Control Protocol/Internet Protocol Trivial FileTransfer Protocol Totally Integrated Automation Special message from a network component to the network management station; based on SNMP User Datagram Protocol Typical SNMP client function. In contrast to a Network Manager, Web-based management does not control and monitor an entire network, but only one network node. It requires a standard Internet browser such as Netscape Communicator or Internet Explorer. Copyright AG 2001 All Rights Reserved Page 23 of 23 Excellence in