PEARLS in .NET

Include QR Code JIS X 0510 in .NET PEARLS

Much is made of this gee whiz feature. And, to be sure, it is a convenience to have a network management system that will create a network map. (One could argue that we should have been keeping the network map up-to-date as we designed and grew the network. Unfortunately, most networks and especially LANs were never really designed, they just grew.) How the mapping function works and what information is available from the map is more important than the map itself. First, the map should be readable. Second, it should permit zooming in and out. In the show-me-the-whole-network mode, the map of a large network will be too dense to read. It should provide the capability to zoom in until the subsystem of interest is displayed. The mapping function from different vendors works with varying degrees of success. There are two basic ways of implementing the mapping function. The network management system can use SNMP information from each agent, or it can observe the traffic on the network. The SNMP approach yields a map more quickly, but can only display managed devices. Tracking traffic flow can theoretically find every interface or port on the network, but could take months of operation to finally determine a map. (In some cases, it is impossible to create a map.) Thus, two points must be made. First, accumulating the information to draw the map is not a 10-minute job. Depending on the size of the network, it could take hours to days to months. Second, the accuracy of the map is dependent on how extensively each node on the network supports SNMP. For example, several prominent vendors don t support standard MIBs. As noted, there are standard MIBs and vendor-specific MIBs. In order for your network management system to utilize the vendor specific MIBs, they must be loaded into the manager function. For normal (here read simple ) networks, the mapping function works well and fairly quickly. That means, it works for Ethernets connected with routers and bridges, where each interface on the router is its own subnet. Today, however, we tend to use fully switched Ethernets where each device is on its own switched port from a LAN switch. The advantage is that each port is buffered so that there are no collisions on the network. A second advantage is that one can create virtual LANs (VLAN) where devices on different ports of the switch can be made members of the same broadcast domain or subnet. This permits you to design traffic flows on the various LAN segments in order to minimize response times and keep broadcast traffic confined to those devices that are members of the same logical net. The disadvantage from a network management system point of view is that it is between difficult and impossible for the mapping function to create a map because there are managed devices hiding behind, or within, other managed devices. This is especially true if the LAN switch doesn t support transparent bridging or standard SNMP MIBs. The next fly in the ointment is the development of ELANs (Emulated LANs). These are similar to VLAN (Virtual LANS), where we are emulating LANs by using an ATM switch and edge devices that are LAN switches. Here again, the ATM switch and edge device may not provide the MIB support necessary to build an accurate map of your network.

[k] 1,000 (103) 1,000,000 1,000,000,000 1,000,000,000,000 1,000,000,000,000,000 (106) (109)

Gartner sees cloud computing as an evolution of business that is no less influential than e-business. Gartner maintains that the very confusion and contradiction that surrounds the term cloud computing signifies its potential to change the status quo in the IT market. Gartner defines cloud computing as a style of computing where massively scalable IT-related capabilities are provided as a service using Internet technologies to multiple external customers. During the past 15 years, a continuing trend toward IT industrialization has grown in popularity as IT services delivered via hardware, software and people are becoming repeatable and usable by a wide range of customers and service providers, said Daryl Plummer, managing vice president and Gartner Fellow. This is due, in part to the commoditization and standardization of technologies, in part to virtualization and the rise of service-oriented software architectures, and most importantly, to the dramatic growth in popularity of the Internet. Plummer said that taken together, these three major trends constitute the basis of a discontinuity that will create a new opportunity to shape the relationship between those who use IT services and those who sell them. Essentially it will mean that users of IT-related services will be able to focus on what the service provides them rather than how the services are implemented or hosted. Gartner maintains that although names for this type of operation have come into vogue at different times utility computing, Software as a Service (SaaS), and application service providers none has garnered widespread acceptance as the central theme for how IT-related services can be delivered globally.

The entire employee database program is shown next. Pay special attention to how each array is accessed. This version of the employee database program is not particularly useful, because the information is lost when the program is terminated. Later in this book, however, you will learn how to store information in a disk file.

// Use the NullReferenceException. using System; class X { int x; public X(int a) { x = a; } public int Add(X o) { return x + o.x; } } // Demonstrate NullReferenceException. class NREDemo { static void Main() { X p = new X(10); X q = null; // q is explicitly assigned null int val;

MATH NOTE The form y = 3x 5 for the equation of a line is called the slopeintercept form. The slope is 3 and the line passes through ( 0, 5) (its y-intercept).

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