??What is ActiveX
ActiveX is a series of computer program distribution and runtime technologies. Developed by Microsoft, ActiveX technologies have been incorporated into almost all of Microsoft's products released in recent years including Windows, Word, Excel, and Internet Explorer. ActiveX-enabled programs can embed features found in other enabled programs, and can incorporate new features within an ActiveX component. For instance, Internet Explorer can open an Excel spreadsheet via ActiveX object linking, and incorporate all the features of Excel within itself. Similarly web designers who wish to incorporate a features not implemented within any of Microsoft's products can write the features as an ActiveX component in any programming language that support it.
ActiveX is a development of Microsoft's Object Linking and Embedding technology. Originally designed to facilitate the copying of non-text objects via Windows' built-in clipboard, OLE was extended to all Microsoft products that support the clipboard. Objects such as pictures, sound, spreadsheets, and more can be embedded in other document types. OLE is itself a manifestation of Dynamic Data Exchange, the original clipboard architecture. The major limitation of OLE that ActiveX overcomes is the fact that OLE can only copy user data between applications, whereas ActiveX can copy executable code. Of course, this requires that the code to be copied actually be present on the system: Excel spreadsheets will not display in Internet Explorer if Excel itself is not installed.
ActiveX logo
The inclusion of ActiveX controls in Internet Explorer has led to hundreds of security threats regarding the browser, many of which are quite serious. ActiveX was enabled by default on all supported IE versions prior to Windows SP2. As IE is an integral part of the Windows operating system, ActiveX components running in IE had access to most of the running system. This was often exploited, and much of today's malware has been distributed this way. However, disabling ActiveX in Internet Explorer leads to problems with legitimate webpages that depend upon embedding objects this way, such as those presenting Flash or QuickTime movies
??What is 802.11
802.11 is a series of IEEE specifications describing wireless data transfer. Most commonly implemented in WiFi applications, 802.11 has become the de-facto wireless connection specification for long-term connection and application function. Only Bluetooth currently competes with 802.11 for single file, non persistent data transfer between consumer electronic devices. However two other wireless specifications, WirelessUSB and WiFiMax, are under rapid development and new gadgets are being introduced that utilize these technologies.
802.11 is now one of the physical layer protocols adapted by TCP/IP, and includes the data link layer in it's specification. While in theory this reduced complexity by reducing the TCP/IP layer stack from five layers to four, in reality the data link layer is implemented in two sublayers. Therefore, 802.11 implementations have one additional layer effectively added to the stack, not one removed. Based on Ethernet protocol techniques and methods, 802.11 handles interference, packet loss, and error correction in a manner consistent with Part 15 of the FCC regulations for unlicensed use of the 2.4 and 5 GHz bands. 802.11, like all Part 15 compliant standards, gives frequency priority to licensed operators and causes them no interference. Additionally, the specification is designed to accept interference from non-malicious licensed users of the band.
802.11 logo
Notable among the 802.11 revisions are revisions 'a', 'b', and 'g'. Each form the basis for different, incompatible WiFi implementations designated by the same letter as the 802.11 revision they are based upon. The first to find widespread use was 802.11b, as it was very similar to the original 802.11 draft specs. Introduced in October 1999, the 'b' specification operates in the popular 2.4 GHz band and provides up to 1.5 MB/sec (11 Mbit/sec) of bandwidth. Although ratified slightly before the 'b' specification, the 'a' specification took longer to adapt as it operates in the less popular 5 GHz band. The high frequency ensures an interference-free transmission, however the short wavelength cannot adequately penetrate common building materials such as steel and concrete. Thus, 802.11a was an unsuitable standard for indoor use despite providing up to 7 MB/sec (54 Mbit/sec) data transfer rate. Three years after the introduction of 802.11a and 802.11b, 802.11g was introduced. This new specification achieves it's 7 MB/sec (54 Mbit/sec) speed in the 2.4 GHz band through OFDM modulation. However, the crowded 2.4 GHz band often severely limits the range of high-speed 802.11g access, and the presence of a compatible 802.11b device on the network brings speeds down to the 'b' specification's maximum.
ليست هناك تعليقات:
إرسال تعليق