Designing and managing an SNA network for growth

Transcription

1 Designing and managing an SNA network for growth by S. M. SCHIFFMAN IBM Tampa, Florida ABSTRACT The IBM Information Network is a nationwide System Network Architecture (SNA) network that offers network services and application offerings to end users. This paper describes the techniques used to design and manage the growth of the network. Emphasis is placed on the design process and the migration and implementation plans to expand the network while still providing 24-hour operation 7 days a week. Areas covered include adding processors, bandwidth, multiplexers, and end user devices. 663

2

3 Designing and Managing an SNA Network for Growth 665 PREFACE The task of designing and managing a complex telecommunication network involves extensive advanced planning. The disciplines of performance and availability analysis, line cost evaluation, network topology, and distributed processing must be employed. The IBM Information Network came into being in 1982 and offers a variety of network services and application offerings to its customers. The network is designed to accommodate a variety of device and system attachments and to be able to grow as the need arises. The following discussions explain the objectives of the network and how the design has been able to meet them. In addition, the flexibility of IBM system network architecture (SNA) is highlighted by using examples of network expansion strategies. NETWORK OBJECTIVES There are many details required to define a network, but a clear set of guiding principles are necessary to make design decisions. In this section, we discuss the major objectives of the IBM Information Network. Provide Nationwide (U.S.) Coverage It is obvious that covering the entire U.S. in a short time is not feasible. Therefore, a design is required that permits constant orderly growth into new cities and geographical areas. This objective contains the main requirement for planning and managing growth. Each extension to the network has to be designed without hindering normal operation. Allow Any Location Access to Application Processing Center(s) Initially, the processing center exists in one location, so traffic must be efficiently routed to it. The main access into the network and subsequently to application processors is from remote concentration points. End users at these locations must have access to multiple systems. Currently, there are two types of IBM 370 operating systems to access: the multiple virtual system (MVS) and virtual machine (VM) systems. Dynamic access to these systems is provided by use of the multisystem networking functions (MSNFs) of SNA. These features will be discussed later. Allow Any Location Access to Any Other Location In addition to providing access to an application-processing center, it is necessary to allow an end user at any remote location to access any other location in the network. For example, this would enable a terminal user in Los Angeles to communicate with an application processor in New York. This network capability is utilized by the Network Services offering of the IBM Information Network. Highlights of this offering will be used as examples for network growth features~ These objectives were the main elements to be satisfied; the subsections that follow list a set of secondary areas to be addressed. Availability In order to provide quality service to end users, various techniques have to be devised to minimize outages due to network growth, moving equipment to new locations, and failures in equipment or environment. This objective has become another main theme guiding the expansion of the network. Attachability The IBM Information Network has to provide a wide range of device attachment. The network supports IBM 3270 displays, SNA terminals, SNA host systems, start/stop terminals and binary synchronous remote job entry work stations and host systems. These devices and systems are afforded local access to the IBM Information Network by attaching them to remote concentrators. This permits connection by costeffective local dial calls or short-distance leased lines. Flexibility Designing a network before the location and the use scenarios of end users are determined provides a challenge. Different terminals, systems, and bandwidth requirements are expected to grow in an unpredictable fashion. Therefore the network has to be designed to handle different mixes of terminals and increasing bandwidth while remaining in full operation. Response Time/Throughput When all of these objectives are under consideration, adequate performance has to remain at the forefront. Therefore, transit delay has to be kept at a minimum even though high bandwidth may not be required for early traffic. With these objectives in mind, the network design, management strategies, and implementations that follow will become clear. But, first let us look at the overall network design,

4 666 National Computer Conference, 1983 Figure I-The IBM Information Network: geographical distribution dissect each portion of the network, and show how designing for growth is accomplished. OVERALL NETWORK DESIGN The design of the IBM Information Network is based on the communication management configuration (CMC) concept, which uses the latest developments in SNA. The main features employ a central-site system to control the network for operations, problem determination, and status. The system used is MVS with the Virtual Telecommunication Access Method (VTAM) in a System 370 and the network control program (NCP) in a series of 3705 communication controllers all combined to operate a multisystem network. In Figure 1 the network topology shows a set of ten remote concentration points linked together with high-speed lines. These concentration points provide local access to end users. The topology shown was built up over a period of time and will be extended in the future. The CMC concept is based on the premise that concentrating control of a geographically distributed network is more efficient than distributing control. As such, the network definition and migration/growth plans are centralized and kept track of on an inventory database. This provides better control over ordering and tracking network components such as telecommunication lines, modems, terminals, communication controllers, and telephone rotaries. It also provides a better perspective on the whole network, thus enabling some economies of scale to be exercised. The topology is modeled to allow for grouping of traffic onto fewer and larger high-speed lines. Modems can be ordered in larger numbers to take advantage of quantity discounts. Not only migration and growth, but also the day-to-day network operational complexity must be controlled. The latest tools available with SNA-the Network Performance Analyzer, Network Problem Determination Aid, Network Communication Control Facility, Terminal Access Facility, Routing Table Generator, and so on-are used to plan and operate the network. As the network expands, a point will be reached where control has to be subdivided to deal with the sheer number of components. The CMC concept allows this to be accomplished by logically dividing network control initially and later planning for additional CMC processors if necessary. The network is controlled from one location in order to concentrate network management expertise. This also provides close control by monitoring use to determine capacity planning. In addition, programs are used to automate many tasks, such as network initialization, backing up lines that

5 Designing and Managing an SNA Network for Growth 667 RJE 55 VM RJE ss TO 7 CITIES 3101 PC 3101 PC PC 3101 Figure 2-The IBM Information Network: network configuration have failed, collecting statistics on trends, and responding to requests that do not require operator intervention. The strategy is to automate more and more operator tasks as they are identified, so that human error will be minimized as the network grows. Figure 2 depicts the network configuration, including the CMC and application processors. An application-processing center may reside at several locations as the need arises. Each one is composed of one or more processors capable of running operating systems such as MVS or VM and is connected to a switching network by a set of 3705INCP multiplexers. The IBM Information Network initially contains a single processing center. Expansion may be accomplished using SNA MSNF features. THE SWITCHING NETWORK The switching network area of Figure 2 is shaded for conspicuousness. It consists of a processor that provides communication management through VTAM and network management tools. This CMC processor is linked to the network by a series of 3705s in a meshed configuration. These multiplexers provide the paths for remotely attached end users to access each of the application processors. The 3705s are configured in two forms; one set is optimized for the maximum number of channel adapters, and the other uses many highspeed (56-Kbytes/sec) lines. These meshed multiplexers form an insulator between the application processors and the remote network. All end user devices are attached to remote multiplexers, where the most frequent network changes occur. The switching 3705s are more stable and are influenced by adding application processors and/or new remote 3705s. Expansion of application processors is accomplished by using a channel adapter connection on a local 3705 and defining the new processor to selected network components (see Figure 3). Once all channel adapters are used, additional 3705s are added by meshing one into the switching network. Advanced planning is necessary to minimize the impact of adding new processors. Keeping in mind the 24-hour operation re-

6 668 National Computer Conference, 1983 CPU CPU CPU ADDING NEW PROCESSORS CMC CPU REMOTE PROCESSING CENTER REMOTE CITY EXPANSION Figure 3-Switching network expansion for new cities, new CPUs, and remote processing centers quirement, the new processor definitions are gradually added to NCPs and VTAMs. This is possible because the absence of the processor is ignored by the network even though it is defined. In addition to locally attached processors, MSNF offers the capability of attaching application processors to the switching network at remote sites. Their attachment is similar to adding remote multiplexers. In the shaded area of Figure 3 a remote processing center is depicted with application processors and communication controllers attached to the switching network. The overall network design is preserved by continuing to attach terminals to remote 3705s. Once again the rudiments of a switching network are taking form at the remote location, with a series of 3705s used as switching controllers to the application processors. As more remote multiplexers are added in new cities, they are connected to the switching network via high-speed digital lines. Initially this is a simple process; ports already available on the second tier of 3705s in the switching network are used. The affected adjacent 3705INCPs may be gradually updated before the new 3705 and line are added. After enough new remote cities are added, the second-tier high-speed ports will finally be exhausted. This requires the addition of more 3705s. A 3705 is first logically added to the configuration, and all the necessary paths and physical connections are determined. Once again, adjacent NCPs are gradually updated and then loaded. When all affected components are synchronized the new 3705 is physically added to the switching network. In this manner the switching network may be expanded while still maintaining normal operation. It should be noted that all remote locations are defined with a primary route and at least one disjoint alternate route to access the application processors (see Figure 4). This definition permits 3705s to be redefined and reinitialized with updated NCPs while the network still operates normally. While reinitialization is in progress the alternate route is used automatically. Once reinitialization is complete, the primary route is available. The SNA alternate-route capability is used as a migration tool for adding new 3705s to the second tier of the switching network and increased bandwidth between the switching network and remote sites. As the network grows, other uses will be found for this migration tool. BANDWIDTH EXPANSION Lines between the switching network and the remote multiplexers are prone to the widest variation of use. As the end user population grows, the load increases on these lines. The transmission group (TO) line feature of SNA is exploited to add necessary bandwidth: A new line is defined and then installed between 3705s; This line is added to a TO and testing is insured by deactivating other lines for short periods. Once the testing is successful, the new line is a full-fledged member of the TO. TOs are also used for adding interim analog lines when digital service is not yet available in an area. In this case the analog lines are included in a TO and are discontinued once the digital lines are added and tested. This process usually requires 30 days to insure that the new line has stabilized.

7 Designing and Managing an SNA Network for Growth 669 MVS VM CMC TPA 3705R 3705R Figure 4-Alternate routes Since experience has shown that line availability varies by area, TGs are defined with multiple lines even where no immediate plan to add lines exists. This aspect of planning ahead is a constant theme for network growth. It enables lines to be added with a minimum of disruption. In this way the use of TGs as a migration tool has become predominant. REMOTE CONCENTRATION As previously mentioned, all end user devices are attached to the IBM Information Network via remotely deployed multiplexers. At each remote concentration point several types of multiplexers are employed. One or more 3705s connect SNA and BSC 3270 devices and systems. Series/Is are used to perform protocol conversion of IBM 3101 and the IBM Personal Computer to full-screen emulated operation. When port capacity is exhausted, additional remote 3705 multiplexers may be added to the network and the Series/Is in tum attached to the 3705s. Both switched and leased connection are possible. An end user choosing switched connection may dial into any location supported by the network. Each remote location is managed from the central CMC site using SNA tools. Both the 3705 and the Series/l are initialized by the CMC network operator. The remote 3705s are loaded with the configuration from a database maintained on the CMC system. The load module is transmitted to the 3705 over the telecommunication lines in the network. The Serieslls are loaded from diskettes resident on each system. This loading is triggered by remote control from the CMC site.

8 670 National Computer Conference, 1983 MARKETING FORECAST ATTACHMENT REQUIREMENTS PERFORMANCE REOUIREMENTS OFFERING REOUIREMENTS DEFINE NETWORK (CONNECTIVITY) PERFORMANCE I AVAILABILITY ANALYSIS COST ANALYSIS Figure 5-Network Services A strategy of updating these configurations no more often than once a month has been chosen. The justification for this approach is based on the availability of a leased line usually being greater than 30 days. Therefore, once a leased-line end user has to be added, waiting 30 days is acceptable. The switched-line user may attach to the network almost immediately, since adequate ports with modems and telephone terminations are planned in advance. This also permits future leased-line users to attach via switched lines in the interim. Managing the switched ports requires constant monitoring of use so that rotaries~ modems, and ports may be allocated for future expansion. Using network tools, connection information on dial port usage is retained. These data are used to project 30 to 90 days ahead, so that the ports may be expanded. The lead time for this activity is critical, since close coordination between the common carrier, the modem supplier, and the IBM Information Network support groups is required. In addition to connecting end user terminals that access IBM Information Network application processors, the remote 3705s also provide connection for Network Services users. In Figure 5 a typical connection configuration is shown. Several terminals in different cities are connected to a customerowned application processor. This connection traverses the network through remote 3705s on an SNA session. A session is initiated by communicating the request to the CMC processor. After the necessary security checks and user identification are completed, the end user is connected to the appropriate processor. Use information about sessions is collected at the remote 3705 and relayed back to the CMC for later, batch processing. In this manner, performance information can be consolidated for the remote 3705s even though both cross-network traffic and IBM Information Network application processor traffic are included. This information is reduced and used for determining when a communication line to a customer host must be upgraded to meet line load and response time objectives. In addition, data on the use of the high-speed switching network lines are also collected. Decisions on adding cross-network lines and upgrading the speed of existing lines are based on these data. Projections are also made for the short and long term. Since digital circuits often have a long lead time before installation, MIGRATIONI IMPLEMENTATION PLAN Figure 6---The planning cycle sometimes more than a year, this advance planning is important. When a line has to be upgraded or added, the strategy used is the same as for adding connections between the switching network and remote nodes. The 3705INCPs are gradually updated and lines are added to existing TGs to minimize network disruption. SUMMARY The design and management of an SN A network providing for growth require advance planning and a well-trained technical staff versed in modeling, performance analysis, topological design, measurement, and cost evaluation. These skills must be integrated in a design team that considers both short- and long-term network growth problems. These range from methods of expanding dial rotaries to major network expansions and restructuring. The process is continuous and iterative. The flow chart in Figure 6 depicts this process as applied to the IBM Information Network. The areas that require special design for growth include 1. Expanding service to new geographical areas 2. Addition of ports for end user equipment 3. Expansion of bandwidth 4. Inclusion of more CPU power for applications All of these requirements must be met while maintaining 24-hour uninterrupted service to end users and reasonable network transit delays. The features of SNA permit many other flexible expansion and operation strategies. In the future, additional CMC configurations may be used to distribute network operation and to improve availability further. This extension may be accomplished by remote deployment of processors attached to the switching network. Thus, by distributing both network management and backup capabilities, long-range goals may be met.