The OSI model is quite similar to TCP / IP model only adds more details in two extra layers while TCP / IP is grouped only five layers. Layers of OSI Model Layer 1: This layer includes all the standard electrical network and all concerning the electronic circuits and a physical network environment such as the types of cables, network cards, etc. Layer 2: The two-layer handles the physical address, ie at this level are considered physical addresses that are assigned to network devices at the time of its creation. Error correction is another of the main functions of layer 2. It is said that The switches and bridges are Layer 2 devices. Layer 3: The three-layer or network layer handles the routing logic that unlike the physical address that is not chosen hardware manufacturers but is assigned by the ISP (Internet Service-provider – News ResultsFiscal fitness beats conquering fatness for New Year’s resolutions New York Daily News – 9 hours agoSaad Healthcare hiring, building new outpatient clinic in Mobile Mobile Press-Register – 7 hours agoTremor Media Acquired ScanScout for $65 Million NYConvergence – 9 hours agoPromotional ResultsMake Yahoo! Your Homepage’>Service Provider) to the end user.
The IP protocol operates at this level as well as network devices like routers or routers. Layer 4: The four-layer or transport layer TCP protocol and operates at this level is where it ensures that data sent from a sending device are received correctly at the receiving device. Layer 5: Session layer 5 or has primary responsibility to establish, maintain and terminate sessions between several machines that communicate with each other, it is this layer that determines who speaks and who listens when there is competition for using a port. Layer 6: The 6 layer or presentation layer is responsible for making the data sent from a computer can be presented in a manner readable by the receiving computer.
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Even when the Internet was in its infancy no more than a few computers connected together, it became apparent the need to synchronize the time. Computers are easily confused especially with the time it can only travel in one direction. Where a communication is sent from a computer and received seems to have arrived before it was sent and this can cause unforeseen problems. Imagine buying an airline ticket only to show up at the airport and find someone who has bought his seat after you did just because he reserved on a computer Acon a slower clock! Dr. David Mills of the University of Delaware, realized the need for a synchronization tool and developed the Network Time Protocol – Network Time Protocol (NTP). Although not the first and only time synchronization protocol is the most used and probably owes its success, now Professor Mills, and his dedicated team for their continued development What began as a protocol synchronization could manage a few milliseconds is now able to keep computer clocks within a few nanoseconds of each other (nano = milli = 1/milesimo 1/milmillonesimo). NTP is hierarchical and is divided into strata.
A clock source is called a Stratum 0, while a server is Stratum 1 NTP, equipment and devices that receive the time from a Stratum 1 server become Stratum 2 and so on. This hierarchical structure means that tens of thousands of devices can be synchronized at once without flooding the NTP server or bandwidth of the network. NTP servers are based on the use of a reference clock. While this can be anything from a wristwatch to a computer system clock does not make sense to use a reference clock that was not exactly himself Most networks using an NTP server using a UTC time source . The UTC, or Coordinated Universal Time is based on the time reported by the incredibly accurate and expensive watches atomic. The time signals of an atomic clock can be set either through the Internet (although the accuracy is variable and depends on the distance), special radio broadcasts issued in several countries (including USA, UK Germany, France and Japan) or through the American GPS (Global Positioning System).
NTP servers distribute this Stratum 0 time source to all devices on the network that connects with the NTP server. The NTP then advance or sustain the system clock to match the timing reference. NTP also has its security measures called authentication. This is a set of encryption keys are used to identify both the client and the server. Unfortunately, authentication is not available in Internet time references and that is why both Microsoft and Novell des sources suggest that hardware be used as timing reference. NTP is currently in version 4 to version 5 in development and is open source and freely available for download through ntp.org Cecilia Chavez is a technical author and specialist in atomic clocks, telecommunications, NTP and synchronization Network Time to help develop dedicated NTP clocks.
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What we say with our worthy representatives to Congress and President Alvaro Uribe V. is; SUVERSIVOS CAUSED SUCH STUDENTS will end the nation, As happens budget request to support public higher education no, no, no … the hilt! to be self-financing, they become research centers and help pay for little salary and pensions of our farmers in Congress and strengthen programs that save the rich peasants national social programs such as Agro secure income for Uribe’s friends and company and our nation achieves security, in order to continue benefiting from the weak financial capital shouting reelection And for those who work in arduous conditions of heat cutting cane, planting flowers, helping in the transportation of oil, working in the factory for more than eight hours without remuneration for time extras, those who lose their jobs for the carpal tunnel destroyed their daily fingering hand, if all those scoundrels who support their families with a minimum wage and pensions may not die in the attempt. That happens not to do as the Colombian Congress, which if they think of their own.
Now to fund campaigns like those left displaced and live in shacks of interest priority, of course, shameless quea the Mayor of Bogota which gives money to those farmers escaped not want to work the same mayor who happened to deliver homes for the disabled that atrocity, the mayor who wants to deliver Internet feed the poor and free with the sacred money that should strengthen the coffers of the most powerful politicians to make campaign-saving democracy, that Mayor Samuel Gee, thank God that something you learn, because at least he wants to give a bit cake the ETB to multinational these days have their crises never deserved and that the privatization of ETB can find relief.
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