rdlc barcode 7: Business Continuity and Disaster Recovery in Software

Implement Code-39 in Software 7: Business Continuity and Disaster Recovery

This section covers the basic mechanics as to how information is processed as it s sent down the protocol stack on a computer. Consult the diagram shown in Figure 2-5 to follow along with this process as PC-A sends data to PC-B. In this example, assume that the data link layer is Ethernet and the physical layer is copper. The first thing that occurs on PC-A is that the user, sitting in front of the computer, creates some type of information, called data, and then sends it to another location (PC-B). This includes the actual user input (application layer), as well as any formatting information (presentation layer). The application (or operating system), at the session layer, then determines whether or not the data s intended destination is local to this computer (possibly a disk drive) or a remote location. In this instance, the user is sending the information to PC-B. We ll assume that the user is executing a telnet connection. The session layer determines that this location is remote and has the transport layer deliver the information. A telnet connection uses TCP/IP and reliable connections (TCP) at the transport layer, which encapsulates the data from the higher layers into a segment. With TCP, as you will see in 9, only a header is added. The segment contains such information as the source and destination port numbers. As you may recall from the section Connection Multiplexing, the source port is a number above 1023 that is currently not being used by PC-A. The destination port number is the well-known port number (23) that the destination will understand and forward to the telnet application. Based on RFC standards, the TCP or UDP source port number really should be above 49,151, but not all operating systems follow this standard verbatim in many cases, the source port number will be above 1,023. The transport layer passes the segment down to the network layer, which encapsulates the segment into a packet. The packet adds only a header, which contains layer 3 logical addressing information (source and destination address) as well as other information, such as the upper layer protocol that created this information. In this example, TCP created this information, so this fact is noted in the packet header, and PC-A places its IP address as the source address in the packet and PC-B s IP address as the destination. This helps the destination, at the network layer, to determine whether the packet is for itself and which upper layer process should handle the encapsulated segment. In the TCP/IP protocol stack, the terms packet and datagram are used interchangeably to describe this PDU. As you will see in 6, many protocols are within the TCP/IP protocol stack ARP, TCP, UDP, ICMP, OSPF, EIGRP, and many others.

Because C++ is a structured (as well as an object-oriented) language, it supports the creation of blocks of code. A block is a logically connected group of program statements that is treated as a unit. In C++, a code block is created by placing a sequence of statements between opening and closing curly braces. In this example,

There s actually one more problem with this ACL. If you guessed the ACL number used on the interface is not correct, then you guessed correctly. Notice that the ACL created has a number of 2, while the application of the ACL on the interface uses 1. To fix this, use the following configuration:

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Application profiles summarize the queries, forms, and reports that access a database as shown in Table 8.3. For forms, the frequency o f using the form for each kind o f operation (insert, update, delete, and retrieval) should be specified. For queries and reports, the dis tribution o f parameter values encodes the number o f times the query/report is executed with various parameter values. Unfortunately, D B M S s are not as helpful to collect applica tion profiles as table profiles. The database designer may need to write specialized software or find third-party software to collect application profiles. Table 8.4 depicts profiles for several applications o f the university database. The fre quency data are specified as an average per unit time period such as per day. Sometimes it

FIGURE 14.29. Variable-angular-velocity cam (schematic).

holds the result of the query. { First; Second;

Enabling WebVPN is an easy proposition. Most WebVPN commands are executed in the WebVPN subcommand mode (webvpn command):

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