DTJ Number 3 September 1987 - Digital Technical Journals

New Productsitoring activities outgrew the capabilities of thissystem. The lack of memory address space andCPU speed. prevented adding new features, andthe forms-based user interface became quitecumbersome . Thus a new monitor developmentproject was initiated, which culminatedin the DECoct monitor, based on the VAXjVMSsoftware.6The DECoct monitor provides the capabilityto centralize network management, automatingmany of the intelligent monitoring fu nctions· discussed in the last section. It also enhancesthe databases, protocols, and user interfacesprovided by NCP, thus allowing the user tomonitor the state of his network more effectively.Centralized ManagementIn centralized management, a centrally locatedorganization (for example, corporate headquarters)assumes responsibility for the managementof key parts of the network. A centralgroup usually has the expertise and resourcesto deal with the more difficult problems ofnetwork management, which require peoplewhose skills are scarce and expensive. Thusthese people are more effective as a central,and therefore shareable, resource. Theirscarcity means that they need easy-to-use toolsto make them productive . There are manyaspects to ease-of-use; for the monitor, it meansproviding users with information in a formthat is easy to understand. Of course, easy-touseprograms often require more computerresources (disk space , memory, CPU time) ,but the overall cost of network managementcan be lowered if the tools make people moreefficient.Centralized DatabaseNetwork problems typically span many nodes. Asystem manager at a component may see thesymptoms of a problem but not have the informationneeded to fully understand it. Only the networkmanager can access all the informationneeded to diagnose and solve problems thataffect the whole network. To do this diagnosisfrom one location, the network manager mustgather and store data in a historical database athis central site . This centralized database is animmensely valuable resource in managing a network,operating even when some of the systemsbeing managed are not.;iShort, Medium, and Lng TermProblems :Network managers have short-, medium-, andlong-term needs for data and for analyses of thatdata. Over a short time period (hours or minutes), the network manager is concerned withdetecting and solving critical network problemsor failures. Such failures m 1 ight cause the com-'pany's network application Ito be unavailable tosupport its business needs for an indeterminateamount of time. To detect problems, the networkmanager needs intelligent analyses of the mostrecent state of the network..Network problems often:arise from multiplecomponent failures. For exmple, in a networkI .that makes use of alternate ]paths and automaticfail-over (such as provided' by the DECoct software), the failure of two or more circuitscan partition the. network. Tbis failure could alsodisrupt a business application that depends onthe network as a resource. Such a partition willnot occur if only one failure takes place . OnIthe other hand, a single faqure can be detectedin several locations. For e*mple, if a point-topointcommunication line fails, that failurewill be recorded at each end of the circuit. Thusthe network manager needs coordinated informationfrom all points noting the failure if he orshe is not to be confused by multiple indicationsof the same problem. Th monitor evaluatesthese communications failures, sorting outduplicate indications and ignoring redundantinformation.Error and traffic statistics are a key means ofdetecting problems in the network. Many ofthese statistics come from the counters built intothe DECoct software. Single counter readings,however, are not immediatly meaningful. To beuseful, counters must be ampled at the beginningand end of an interval, and their differencecan then be used to compute important statistics.For example, dividing the difference in counterreadings by the length of ,the time period willyield the rate (such as traffic or error rate) perinterval. The DECoct mohitor computes boththese statistics as well as niany others.In a medium time period (hours or days) , thenetwork manager must note developing trendsthat may predict incipient problems that mightbe prevented. Certainly, increasing error rates ortraffic levels could signal developing problems.The DECoct monitor provides displays to signalIDigital TecbnlcaljournalNo . 3 September 1986123