 that occurred. 21.4 SURVIVABILITY - WHERE NETWORK MANAGEMENT REALLY PAYS In Ref. 3, Steven Dauber lists five network-specific characteristics that the trouble- shooter should have familiarity with or data on. A. Network Utilization. What is the average network utilization? How does it vary through the work day? Characteristics of congestion, if any, should be known. Also, where and under what circumstances might it be expected? B. Network Applications. What are the dominant applications of the network? What version numbers is it running? C. Network Protocol Software. What protocols are running on the network? What are the performance characteristics of the software, and are these characteristics being achieved? D. Network Hardware. Who manufactured the network interface controllers, media attachment units, servers, hubs, and other connection hardware? What versions are they? What are their performance characteristics? Expected? Met? E. Internetworking Equipment. Who manufactured the repeaters, bridges, routers, and gateways on the network? What versions of software and firmware are they run- ning? What are the performance characteristics? What are the characteristics of the interfaced network that are of interest? 21.4.1.2 Developing a Hypothesis. In this second step, we make a statement as to the cause of the problem. We might say that T1 or E1 frame alignment is lost because of deep fades being experienced on the underlying microwave transport network. Or we might say that excessive frames being dropped on a frame relay network is due to congestion being experienced at Node B? Such statements cannot be made without some strong bases to support the opinion. Here is where the knowledge and experience of the troubleshooter really pays. Cer- tainly there could be other causes of E1 or T1 frame misalignment, but if underlying microwave is involved, that would be a most obvious place to look. There could be other reasons for dropping frames in a frame relay system. Errored frames could be one strong reason. 21.4.1.3