Article Computers Technology

A Virtual Local Area Network (VLAN) is a group of hosts that feature a like set of requirements and can communicate as though they were all connected via the same wires. However
unlike a traditional LAN
a VLAN is not necessarily all in the same place
and the hosts involved in the network can be located practically anywhere. All VLANs have the exact same attributes as a traditional physical local area network
though they can be configured via software instead of having to actually relocate the hosts.

Many VLANs are designed as replacements to the services that are traditionally provided by routers on physical LANs. VLANs are able to tackle issues like network management
security
and scalability with ease.

VLANs are known as Layer 2
or Data Link layer
constructs which transfer data between network nodes. Because they are Layer 2 constructs
they can interface with Layer 3 IP subnets with a one to one relationship.

How are VLANs designed?

The IEEE assigned IEEE 802.1Q as the protocol by which to configure virtual LANs. IEEE 802.1Q provides for a header with a 2-byte protocol identifier and another 2-byte tag control information. These are known as TPID and TCI
respectively. The TPID is fixed at 0x8100 while the TCI contains information pertaining to the user priority
canonical format indicator
and VLAN identifier.

What are the two types of VLAN memberships?

VLAN membership can be assigned in one of two ways. Static or Dynamic.

A Static VLAN is also known as a port based VLAN. These types of VLANs are created by assigning specific ports to a VLAN. As new devices enter into the VLAN network
the device assumes a specific port. If end users change ports but require access to the same VLAN
network administrators are required to assign new port to VLAN assignments for the new port.

A Dynamic VLAN is designed to be easily configured using software. The most common software for designing dynamic VLANs is CiscoWorks
a program developed by Cisco. A VLAN Management Policy Server (VMPS) must be set up first for a dynamic VLAN. This server will allow the VLAN to automatically switch ports whenever new devices connect to the VLAN. It uses information such as the device’s ports
unique usernames
and MAC addresses to determine whether or not to change ports to fit the needs of the incoming device.

A torrent file is the file that is transferred among users using the torrent technology. The file extension used by torrent files is .torrent. Torrent files
when added into a torrent application
can be distributed among numerous amounts of people without the need of any major hardware costs and server fees on a particular individual. This is because each user supplies bits of the full torrent file to users without those particular bits
while receiving bits that they do not yet have. Therefore
torrent files can also be shared relatively quickly.


History
Torrent technology was first planned and developed by Bram Cohen in April 2001. After months of development
it first went public in 2 July
2001
Today
Cohen’s technology is widely used. Although there are no specific measurements
it is considered as one of the most significantly used protocols in the Internet today.


Behind the Technology
The torrent technology is operated by a torrent client sending bits of the torrent file through a torrent protocol. A torrent client would be for example a personal computer while the torrent file can be of any file in the .torrent format.

For the sharing to begin
first a user must create a .torrent file (eg. File.torrent). A torrent file contains information
such as the tracker
the main computer distributing the file first
and the metadata
information about the files in the torrent file. People wishing to obtain the information must first download the torrent file (in this case
File.torrent)
run it with their torrent application
and then connect with the tracker
which will give orders on where to download what bits of the torrent file.


Torrent Files vs. HTTP Files
Although torrent files and its sharing are technically a transfer of files over the network
it has its strengths compared to the old-school HTTP downloading style. Firstly
when downloading files
web browsers will make one HTTP GET request through one TCP socket. However
torrent files make numerous amounts of small data requests over many TCP sockets. Also
HTTP will download in an order—what is first will be downloaded first; however torrents download in a random way—whatever is of high availability will be downloaded first.

This is exactly why the torrent files have its strengths; it doesn’t need much financial back
it has a higher redundancy
and a better resistance to potential abuse from flash crowds than what would be a frequent thing with HTTPs. However
as with everything
there is a downside. It takes a bit of time for downloads to be running in full throttle
as connecting to other peers can tae time. Also
becoming an effective uploader also takes time. Not to forget
while torrent file downloading will reach immensely high speeds
the speed will eventually fall near the end of the download as availability of the bits of the torrent file decrease.


Sharing Torrents and Files
First a user browses through the Internet looking for torrent files. Once a torrent file is obtained
the user will connect it through a torrent application and connect with the tracker. Then
the user will begin to download off of seeders and a group of peers known as the “swarm.” If there is one seeder
the user will directly connect to that seeder and begin to download
but eventually start to exchange files with other peers too
which lessens the burden on the seeder.


Applications of Torrent Files
Surprisingly
torrent files are widely used today by many individuals and some corporations.
 Some bands like “Ween” uses torrent files to distribute their free albums
 .torrent files are increasingly used by Podcasters to meet the high demands of these radio MP3s
 The game America’s Army uses torrent files to release their updates and patches for the games
 An immense number of open source and free softwares utilize torrent files to increase availability and awareness of the projects


Torrent Files’ Limitations
Although torrent files seem to be another great way to download and share files
it has some limitations such as security issues.
 IP Address Exposed: The use of torrent files can lead to anonymity issues
as all IP addresses of current and potentially previous swarm users can be found and abused
 Internet Speeds: It is best to use broadband when sharing torrent files
so dial-up users cannot take full advantage of the torrent technology
 Leeching Problem: While sharing torrent files is good
it doesn’t have many incentives behind it. Thus
there is no real reason to continue to seed after the download has finished. To fix this issue
some torrent sites have begun to limit the download speeds of users who do not upload often.


Free Torrent Applications to Download Torrent Files
In today’s market there are both quality free open source and paid products to download torrent files.
 BitTorrent: BitTorrent is the first and official torrent client made by Bram Cohen himself. It is supported in major operating systems such as Microsoft Windows
Apple
and Linux.
 Azuerus (Vuze): This is also a widely used torrent client first released in SourceForge in June 2003. Released under the GNU General Public License
Azuerus is a constantly developed
free client.
 ตTorrent (uTorrent): uTorrent
also known as microTorrent
is a torrent client written in C++. Because of its small size but a powerful interface
it is another widely used free torrent client. It was first released on December 7
2006
between BitTorrent
Inc. and Ludvig Strigeus
but was later fully acquired by BitTorrent
Inc. because of the application’s popularity
size
and power.

Proxy sites are web pages that provide Internet users with the ability to browse web sites that may be blocked by a content filter of some type. By making use of the proxy site as the portal to the blocked site
it is possible to circumvent the work of whatever filter is in place. At the same time
the proxy site also helps to mask the visit to the site
so that there is less evidence that the content filter was not successful in preventing the visit.

How Does A Proxy Site Work?

Essentially
the proxy site will provide the same ability to browse the Internet as any other browser. What is a little different is that instead of being able to conduct general searches for content
a proxy site allows the user to key in a specific web address and be directed to that specific page in a window that resides on the proxy site. This accomplishes two things. First
the window is coded as part of the proxy site address and not the actual web site the user is visiting. Second
any information cached on in the temporary Internet files will appear to be information related to the proxy site
and not the blocked web site.

Why Use A Proxy Site?

One of the legitimate uses of a proxy site is to get around blocked content that may contain one or two words that the filter has identified as inappropriate for viewing. Many companies make use of filters to limit the ability of employees to spend time looking at web pages that are not related to job functions in some manner. This is usually accomplished with the use of key words that programmed into the filter
which in turn blocks any page or site with those words present. While this does block access to a number of sites that have nothing to do with work
they can also inhibit access to pages and glossaries that are designed to be helpful in many job positions.

When this is the case
an employee may choose to use a proxy site to get around the block and be able to get to a page that he or she legitimately needs to view in order to accomplish a work related task. Since using a proxy site does not take much longer than using a browser window
it is much faster than calling technical support and trying to get authorization to remove a given word from the filter list.

Another advantage of using the proxy site is that the IP address of the user is not logged. This can be a great way to get around the proliferation of adware and spyware that is all too often connected to a given web site. Using the proxy site means less cleanup for the virus protection software to handle
and thus less resources required to keep the workstation clear of problems.

A netmask calculator is basically a script or a program that automatically calculates the netmask numbers for you. Netmask is simply a code of numbers that is used to correctly transfer messages among machines in the same subnet. So
a netmask would work together with the router to determine whether the data goes. For example
if the host’s IP address was 63.243.31.41 and the netmask was 255.255.255.0
the netmask is responsible for telling the machine what numbers in IP address are the subnet and what numbers in the IP address is the machine. In this case
63.172
would be the subnet part while 41 would be the machine part. So
any machine in the 63.172.202 would be part of the (local) subnet and thus
the netmask is exactly what assists in differentiating the IP address.


Behind the Calculation of a Netmask
Before anything else
it is advised to use freely available online netmask calculators as most modern equipments do not need a full understanding of how the netmask works to correctly configure them. In fact
most of the newer models have been hard coded to force a 255.255.255.0 netmask. Nonetheless
such calculating knowledge in needed when dealing with older equipments.

Firstly an internet protocol (IP) address is divided into three main sections when looking at the first octet (xxx.xxx.xxx.xxx): Class A
Class B
and Class C. One of the rules of the IP address are that Class A should be 0-127
Class B should be 128-191
and Class C should be 192-222 with everything else reserved for a special reason. Basically
these classes in the IP addresses are what determine the netmask. Class A means a netmask of 255.0.0.0
Class B means a netmask of 255.255.0.0
and Class C means a netmask of 255.255.255.0. Thus
a simple knowledge of which class implies which netmask is the key to calculating the netmask.


Free Online Netmask Calculators
Again
most of the modern equipments used today have been hardcoded to have a netmask of 255.255.255.0. However
there are also readily available scripts and softwares available that can help in the calculation.

A Multilayer PCBs consist of multiple layers of electronic components placed over each other.

Through-hole construction was the technology that was used to deal with planting the electrical components through the holes on the Printed Board Curcuit and then soldering them together. When this technology was found wanting in complex cases
Point-to-Point construction technology evolved. This proved to be better than its predecessor
but in no way is it comparable to a multilayer PCB. The development of multilayer PCB has allowed electronic companies to drastically cut down on the cost and size of their products.

The functionality of a multilayer Printed Board Circuit depends on the internal connections between the various components that make up the entire device. Until and unless these components work in tandem
the device is non-functional. In the case of most technology
the urge to improve product performance makes the products bulky
whereas the flexible design of the multilayer PCBs has entirely replaced the rigid single-layered PCB design. The high-class wiring and the flexible parts have improved the performance of many products
especially automated and complex devices such as computers and cellular phones. Technology today has come a long way
culminating in the manufacture of multilayer PCBs that can contain as many as twenty-four layers
depending on usage and the complexity of the product itself. Multilayered PCBs have also facilitated the ease of manufacturing
since most of them are pre-mounted and prefabricated. Although manufacturing these prefabricated multilayered PCBs is a complex process
the final stage has now become a matter of assembly rather than manufacturing.

Any discussion of this technology would be incomplete without mentioning the tools and materials that are required for using a multilayer PCB. These are:

*Powerful drill
*Copper etcher
*Laminating press
*Copper plating cell
*And most importantly - a well-ventilated area

The reasons behind the development of the multilayer PCB are numerous
although some may think the technology was unnecessary while standard PCBs were doing fine. As discussed earlier
a multilayer PCB has a more flexible structure and can considerably reduce the size of the device. This is not the only reason. The cost of production using conventional PCBs was very high and costs only increased with new developments. By contrast
a multilayer PCB
in addition to providing revolutionary on-board components
more often than not needs only reprogramming. Moreover
mass production has become easier due to prefabricated multilayered PCBs. Instant installation or assembly of multilayer PCBs means electronic companies have definitely experienced a rise in their production rates.

In case you are wondering about the longevity or quality of these circuit boards
they are very well packaged and can be left as they are for future use. Once each board is completed
it is thoroughly tested to make sure that it functions properly. In cases of failure
the repair process is easy and can be achieved by replacing the board itself instead of resorting to component-level troubleshooting.