How Torrent Works Plus Term Definition

Alot of people just use torrent softwares to download .torrent files but doesn't actually know the operational mechanism, well below is an explanation of how it works...enjoy your reading

Many people are still unaware of what exactly BitTorrent is or what it does. BitTorrent is a P2P protocol, or method, that allows people to share data much more efficiently and at much greater transfer speeds than previous file-sharing software like KaZaA, Morpheus, and WinMX. These programs were Direct Connect types in that each person connected directly and solely to one other user in order to share files. The drawback of this is that the person receiving the data is limited by the upload connection speed of the person sending it.

What BitTorrent does is remove this limitation by allowing a virtually unlimited number of people to connect to one another and share the same file at the same time. Instead of being limited by the upload speed of the other user one is suddenly in the welcome position of being limited by ones own download speed.
The idea behind BitTorrent is to allow massive distribution of popular files without penalizing the source by soaring bandwidth costs and possible crashes due to demand that exceeds the capability of the server. In this way, anyone who creates a popular program, music file or other product can make it available to the public regardless of assets, even if the file becomes highly popular.

To understand how BitTorrent functions, first consider how normal downloading works. Personal computers connected to the Internet are known as clients while the websites visited reside on Internet servers. Servers “serve up information” to clients. If you surf to a site and click on a link to download a program, you create a one-on-one connection to that server that uses whatever bandwidth is necessary to serve you the file. When you have received the entire file, the connection is released so the server can utilize that stream of bandwidth for handling other connections.

The problem arises when unusually high numbers of clients visit a site simultaneously. This can cause the server to effectively run out of available bandwidth and “crash.” When this happens, clients are refused a connection. “The site is down.”


To avoid this, BitTorrent creates a different networking scheme. It uses the other clients who are also downloading the file to effectively act as servers to one another, simultaneously uploading the parts of the file received to others requesting the file. Hence, when you click on a file to download, several connections will be made to receive “slices” of the file that combine to create the entire file. Meanwhile, as you are downloading these “slices” you are also uploading them to anyone else that needs the parts you are receiving. Once the entire file is received it is considered polite to keep your client connected to act as a seed. A seed refers to a source that has the entire file available.

In this way BitTorrent relieves the burden of the servers but more significantly it makes it possible for anyone to disseminate a file quickly and easily without requiring expensive servers or an infrastructure of distribution. If the demand is there, the file will spread.

TERMINOLOGY
Torrent

Usually this refers to the small metadata file you receive from the web server (the one that ends in .torrent.) Metadata here means that the file contains information about the data you want to download, not the data itself. This is what is sent to your computer when you click on a download link on a website. You can also save the torrent file to your local system, and then click on it to open the BitTorrent download. This is useful if you want to be able to re-open the torrent later on without having to find the link again.
In some uses, it can also refer to everything associated with a certain file available with BitTorrent. For example, someone might say “I downloaded that torrent” or “that server has a lot of good torrents”, meaning there are lots of good files available via BitTorrent on that server.

Peer

A peer is another computer on the internet that you connect to and transfer data. Generally a peer does not have the complete file, otherwise it would be called a seed. Some people also refer to peers as leeches, to distinguish them from those generous folks who have completed their download and continue to leave the client running and act as a seed.

Seed

A computer that has a complete copy of a certain torrent. Once your client finishes downloading, it will remain open until you click the Finish button (or otherwise close it.) This is known as being a seed or seeding. You can also start a BT client with a complete file, and once BT has checked the file it will connect and seed the file to others. Generally, it’s considered good manners to continue seeding a file after you have finished downloading, to help out others. Also, when a new torrent is posted to a tracker, someone must seed it in order for it to be available to others. Remember, the tracker doesn’t know anything of the actual contents of a file, so it’s important to follow through and seed a file if you upload the torrent to a tracker.

Reseed

When there are zero seeds for a given torrent (and not enough peers to have a distributed copy), then eventually all the peers will get stuck with an incomplete file, since no one in the swarm has the missing pieces. When this happens, someone with a complete file (a seed) must connect to the swarm so that those missing pieces can be transferred. This is called reseeding. Usually a request for a reseed comes with an implicit promise that the requester will leave his or her client open for some time period after finishing (to add longevity to the torrent) in return for the kind soul reseeding the file.

Swarm

The group of machines that are collectively connected for a particular file. For example, if you start a BitTorrent client and it tells you that you’re connected to 10 peers and 3 seeds, then the swarm consists of you and those 13 other people.

Tracker

A server on the Internet that acts to coordinate the action of BitTorrent clients. When you open a torrent, your machine contacts the tracker and asks for a list of peers to contact. Periodically throughout the transfer, your machine will check in with the tracker, telling it how much you’ve downloaded and uploaded, how much you have left before finishing, and the state you’re in (starting, finished download, stopping.) If a tracker is down and you try to open a torrent, you will be unable to connect. If a tracker goes down during a torrent (i.e., you have already connected at some point and are already talking to peers), you will be able to continue transferring with those peers, but no new peers will be able to contact you. Often tracker errors are temporary, so the best thing to do is just wait and leave the client open to continue trying.

Downloading

Receiving data FROM another computer.

Uploading
Sending data TO another computer.

Share-Ratio

If you are using the experimental client with the stats-patch, you will see a share rating displayed on the GUI panel. This is simply the ratio of your amount uploaded divided by your amount downloaded. The amounts used are for the current session only, not over the history of the file. If you achieve a share ratio of 1.0, that would mean you’ve uploaded as much as you’ve downloaded. The higher the number, the more you have contributed. If you see a share ratio of “oo”, this means infinity, which will happen if you open a BT client with a complete file (i.e., you seed the file.) In this case you download nothing since you have the full file, and so anything you send will cause the ratio to reach infinity. Note: The share rating is just a number that is displayed for your convenience. It does not directly affect any aspect of the client at all. In general, out of courtesy to others you should strive to keep this ratio as high as possible, of course.

Distributed Copies

In some versions of the client, you will see the text “Connected to n seeds; also seeing n.nnn distributed copies.” A seed is a machine with the complete file. However, the swarm can collectively have a complete copy (or copies) of the file, and that is what this is telling you. Referring again to the “people at a table” analogy, consider the case where the book has 10 pages, and person A has pp.1-5 and B has pp.6-10. Collectively, A and B have a complete copy of the book, even though no one person has the whole thing. In other words, even if there are no seeds, as long as there is at least one distributed copy of the file everyone can eventually get a complete file. Meditate on this, the Zen of BitTorrent, grasshopper.

Choked

This is a term used in the description of the BitTorrent protocol. It refers to the state of an uploader, i.e. the thread that sends data to another peer. When a connection is choked, it means that the transmitter doesn’t currently want to send anything on that link. A BT client signals that it’s choked to other clients for a number of reasons, but the most common is that by default a client will only maintain –max_uploads active simultaneous uploads, the rest will be marked choked. (The default value is 4 and this is the same setting that experimental client GUI lets you adjust.) A connection can also be choked for other reasons, for example a peer downloading from a seed will mark his connection as choked since the seed is not interested in receiving anything. Note that since each connection is bidirectional and symmetrical, there are two choked flags for each connection, one for each Tx endpoint.

DMZ - Demilitarized Zone

Definition: 

 

 In computer networking, DMZ is a firewall configuration for securing local area networks (LANs). In a DMZ configuration, most computers on the LAN run behind a firewall connected to a public network like the Internet. One or more computers also run outside the firewall, in the DMZ. Those computers on the outside intercept traffic and broker requests for the rest of the LAN, adding an extra layer of protection for computers behind the firewall.

Traditional DMZs allow computers behind the firewall to initiate requests outbound to the DMZ. Computers in the DMZ in turn respond, forward or re-issue requests out to the Internet or other public network, as proxy servers do. (Many DMZ implementations, in fact, simply utilize a proxy server or servers as the computers within the DMZ.) The LAN firewall, though, prevents computers in the DMZ from initiating inbound requests.

DMZ is a commonly-touted feature of home broadband routers. However, in most instances these features are not true DMZs. Broadband routers often implement a DMZ simply through additional firewall rules, meaning that incoming requests reach the firewall directly. In a true DMZ, incoming requests must first pass through a DMZ computer before reaching the firewall.
 

OR


In computer networks, a DMZ (demilitarized zone) is a computer host or small network inserted as a "neutral zone" between a company's private network and the outside public network. It prevents outside users from getting direct access to a server that has company data. (The term comes from the geographic buffer zone that was set up between North Korea and South Korea following the UN "police action" in the early 1950s.) A DMZ is an optional and more secure approach to a firewall and effectively acts as a proxy server as well.

In a typical DMZ configuration for a small company, a separate computer (or host in network terms) receives requests from users within the private network for access to Web sites or other companies accessible on the public network. The DMZ host then initiates sessions for these requests on the public network. However, the DMZ host is not able to initiate a session back into the private network. It can only forward packets that have already been requested.


Users of the public network outside the company can access only the DMZ host. The DMZ may typically also have the company's Web pages so these could be served to the outside world. However, the DMZ provides access to no other company data. In the event that an outside user penetrated the DMZ host's security, the Web pages might be corrupted but no other company information would be exposed. Cisco, the leading maker of router s, is one company that sells products designed for setting up a DMZ.


OR

What is a DMZ?

The term DMZ Stands for "demilitarized zone," and in the computer world, it refers to a buffer zone that separates the Internet and your private LAN. (Note: Microsoft calls this a "Screened Subnet"). It's considered a separate network that is more trusted than the Internet but less trusted than the internal LAN. Many SOHO router vendors have taken to using the term "DMZ." In fact, those products are simply bypassing their filters and NAT protection when they set up a "DMZ" and forwarding all traffic to a "default host." This should not be confused with a true DMZ.

One way to create a DMZ is with a machine that has three NICs in it -- one for the WAN connection, one for the DMZ network and one for the internal network. This is one method of creating a DMZ, but it is not the preferred method. This configuration allows the security of all three networks to lie in one system. If your machine containing all three NICs is compromised, so is your DMZ and your private network. Basically, you are allowing the Internet to "touch" the very same machine that determines how secure your internal LAN is, and this is not a good thing.

A better way to do this is with three separate networks. The way this is accomplished is with two "firewall" devices -- one on the border of your WAN and one on the border of your internal network. Let us say that you have a broadband router/switch and a Checkpoint firewall. You would put your router/switch on your border (right behind your modem). That becomes your DMZ switch. You use one of the ports to connect your bastion host/public server. This is the machine that is running the service that you want people to be able to connect to from the outside. This may be a website, an FTP server or a multi-player game. You want this machine to be hardened to some degree, meaning that it is all the way patched and is not running anything that is vulnerable (although the border device affords it some protection via NAT). As a general rule, though, you want anything put in the DMZ to be resistant to attacks from the Internet since public access is the reason that you are putting it out there in the first place.

Now, to that same switch, you are going to attach another network cable that goes to your Checkpoint firewall. Your firewall (this is going to be the better of the two firewalls that you have, so if you have a Checkpoint and a Netgear, you should use the Netgear on the border and the Checkpoint box on this one) is going to have two NICs in it -- one for the DMZ side and one for the private LAN side. Connect the cable to the DMZ side of the internal firewall, and on the other side of the firewall (the private LAN side), you connect a cable to another hub/switch that all of your LAN computers will connect to.

If that was confusing, think of it this way:

------------
Internet to Modem
Modem to Router
Router to DMZ Hub/Switch
DMZ Switch to WEB/FTP/Game Server
...and...
DMZ Switch to Firewall External NIC
Firewall Internal NIC to Internal Hub/Switch
Internal Hub/Switch to Internal Systems
------------

What this does is allow you to completely segment your network in terms of trust. You can initiate connections to the DMZ and to the Internet, but neither of those two networks can initiate connections to you. Essentially, you are saying that you don't trust those two networks, and they are considered completely separate from your internal LAN. This way, if your Host in DMZ is compromised, the intruder will not be able to compromise the other computers in your LAN.

The power is further extended by the fact that you can use NAT on your border device to pass only the ports needed into your DMZ. So, if you are only running a web server, then you only pass TCP 80 to your DMZ machine running that daemon; all other connection requests are refused at the border router/firewall.